Merge tag 'core-rcu-2021-02-17' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull RCU updates from Ingo Molnar:
 "These are the latest RCU updates for v5.12:

   - Documentation updates.

   - Miscellaneous fixes.

   - kfree_rcu() updates: Addition of mem_dump_obj() to provide
     allocator return addresses to more easily locate bugs. This has a
     couple of RCU-related commits, but is mostly MM. Was pulled in with
     akpm's agreement.

   - Per-callback-batch tracking of numbers of callbacks, which enables
     better debugging information and smarter reactions to large numbers
     of callbacks.

   - The first round of changes to allow CPUs to be runtime switched
     from and to callback-offloaded state.

   - CONFIG_PREEMPT_RT-related changes.

   - RCU CPU stall warning updates.

   - Addition of polling grace-period APIs for SRCU.

   - Torture-test and torture-test scripting updates, including a
     "torture everything" script that runs rcutorture, locktorture,
     scftorture, rcuscale, and refscale. Plus does an allmodconfig
     build.

   - nolibc fixes for the torture tests"

* tag 'core-rcu-2021-02-17' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (130 commits)
  percpu_ref: Dump mem_dump_obj() info upon reference-count underflow
  rcu: Make call_rcu() print mem_dump_obj() info for double-freed callback
  mm: Make mem_obj_dump() vmalloc() dumps include start and length
  mm: Make mem_dump_obj() handle vmalloc() memory
  mm: Make mem_dump_obj() handle NULL and zero-sized pointers
  mm: Add mem_dump_obj() to print source of memory block
  tools/rcutorture: Fix position of -lgcc in mkinitrd.sh
  tools/nolibc: Fix position of -lgcc in the documented example
  tools/nolibc: Emit detailed error for missing alternate syscall number definitions
  tools/nolibc: Remove incorrect definitions of __ARCH_WANT_*
  tools/nolibc: Get timeval, timespec and timezone from linux/time.h
  tools/nolibc: Implement poll() based on ppoll()
  tools/nolibc: Implement fork() based on clone()
  tools/nolibc: Make getpgrp() fall back to getpgid(0)
  tools/nolibc: Make dup2() rely on dup3() when available
  tools/nolibc: Add the definition for dup()
  rcutorture: Add rcutree.use_softirq=0 to RUDE01 and TASKS01
  torture: Maintain torture-specific set of CPUs-online books
  torture: Clean up after torture-test CPU hotplugging
  rcutorture: Make object_debug also double call_rcu() heap object
  ...

Documentation/RCU/Design/Expedited-Grace-Periods/Expedited-Grace-Periods.rst

@@ -38,7 +38,7 @@ sections.
 RCU-preempt Expedited Grace Periods
 ===================================
 
-``CONFIG_PREEMPT=y`` kernels implement RCU-preempt.
+``CONFIG_PREEMPTION=y`` kernels implement RCU-preempt.
 The overall flow of the handling of a given CPU by an RCU-preempt
 expedited grace period is shown in the following diagram:
 
@@ -112,7 +112,7 @@ things.
 RCU-sched Expedited Grace Periods
 ---------------------------------
 
-``CONFIG_PREEMPT=n`` kernels implement RCU-sched. The overall flow of
+``CONFIG_PREEMPTION=n`` kernels implement RCU-sched. The overall flow of
 the handling of a given CPU by an RCU-sched expedited grace period is
 shown in the following diagram:
 

Documentation/RCU/checklist.rst

@@ -70,7 +70,7 @@ over a rather long period of time, but improvements are always welcome!
 	is less readable and prevents lockdep from detecting locking issues.
 
 	Letting RCU-protected pointers "leak" out of an RCU read-side
-	critical section is every bid as bad as letting them leak out
+	critical section is every bit as bad as letting them leak out
 	from under a lock.  Unless, of course, you have arranged some
 	other means of protection, such as a lock or a reference count
 	-before- letting them out of the RCU read-side critical section.
@@ -129,9 +129,7 @@ over a rather long period of time, but improvements are always welcome!
 		accesses.  The rcu_dereference() primitive ensures that
 		the CPU picks up the pointer before it picks up the data
 		that the pointer points to.  This really is necessary
-		on Alpha CPUs.	If you don't believe me, see:
-
-			http://www.openvms.compaq.com/wizard/wiz_2637.html
+		on Alpha CPUs.
 
 		The rcu_dereference() primitive is also an excellent
 		documentation aid, letting the person reading the
@@ -214,9 +212,9 @@ over a rather long period of time, but improvements are always welcome!
 	the rest of the system.
 
 7.	As of v4.20, a given kernel implements only one RCU flavor,
-	which is RCU-sched for PREEMPT=n and RCU-preempt for PREEMPT=y.
+	which is RCU-sched for PREEMPTION=n and RCU-preempt for PREEMPTION=y.
 	If the updater uses call_rcu() or synchronize_rcu(),
-	then the corresponding readers my use rcu_read_lock() and
+	then the corresponding readers may use rcu_read_lock() and
 	rcu_read_unlock(), rcu_read_lock_bh() and rcu_read_unlock_bh(),
 	or any pair of primitives that disables and re-enables preemption,
 	for example, rcu_read_lock_sched() and rcu_read_unlock_sched().

Documentation/RCU/rcubarrier.rst

@@ -9,7 +9,7 @@ RCU (read-copy update) is a synchronization mechanism that can be thought
 of as a replacement for read-writer locking (among other things), but with
 very low-overhead readers that are immune to deadlock, priority inversion,
 and unbounded latency. RCU read-side critical sections are delimited
-by rcu_read_lock() and rcu_read_unlock(), which, in non-CONFIG_PREEMPT
+by rcu_read_lock() and rcu_read_unlock(), which, in non-CONFIG_PREEMPTION
 kernels, generate no code whatsoever.
 
 This means that RCU writers are unaware of the presence of concurrent
@@ -329,10 +329,10 @@ Answer: This cannot happen. The reason is that on_each_cpu() has its last
 	to smp_call_function() and further to smp_call_function_on_cpu(),
 	causing this latter to spin until the cross-CPU invocation of
 	rcu_barrier_func() has completed. This by itself would prevent
-	a grace period from completing on non-CONFIG_PREEMPT kernels,
+	a grace period from completing on non-CONFIG_PREEMPTION kernels,
 	since each CPU must undergo a context switch (or other quiescent
 	state) before the grace period can complete. However, this is
-	of no use in CONFIG_PREEMPT kernels.
+	of no use in CONFIG_PREEMPTION kernels.
 
 	Therefore, on_each_cpu() disables preemption across its call
 	to smp_call_function() and also across the local call to

Documentation/RCU/stallwarn.rst

@@ -25,7 +25,7 @@ warnings:
 
 -	A CPU looping with bottom halves disabled.
 
--	For !CONFIG_PREEMPT kernels, a CPU looping anywhere in the kernel
+-	For !CONFIG_PREEMPTION kernels, a CPU looping anywhere in the kernel
 	without invoking schedule().  If the looping in the kernel is
 	really expected and desirable behavior, you might need to add
 	some calls to cond_resched().
@@ -44,7 +44,7 @@ warnings:
 	result in the ``rcu_.*kthread starved for`` console-log message,
 	which will include additional debugging information.
 
--	A CPU-bound real-time task in a CONFIG_PREEMPT kernel, which might
+-	A CPU-bound real-time task in a CONFIG_PREEMPTION kernel, which might
 	happen to preempt a low-priority task in the middle of an RCU
 	read-side critical section.   This is especially damaging if
 	that low-priority task is not permitted to run on any other CPU,
@@ -92,7 +92,9 @@ warnings:
 	buggy timer hardware through bugs in the interrupt or exception
 	path (whether hardware, firmware, or software) through bugs
 	in Linux's timer subsystem through bugs in the scheduler, and,
-	yes, even including bugs in RCU itself.
+	yes, even including bugs in RCU itself.  It can also result in
+	the ``rcu_.*timer wakeup didn't happen for`` console-log message,
+	which will include additional debugging information.
 
 -	A bug in the RCU implementation.
 
@@ -292,6 +294,25 @@ kthread is waiting for a short timeout, the "state" precedes value of the
 task_struct ->state field, and the "cpu" indicates that the grace-period
 kthread last ran on CPU 5.
 
+If the relevant grace-period kthread does not wake from FQS wait in a
+reasonable time, then the following additional line is printed::
+
+	kthread timer wakeup didn't happen for 23804 jiffies! g7076 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402
+
+The "23804" indicates that kthread's timer expired more than 23 thousand
+jiffies ago.  The rest of the line has meaning similar to the kthread
+starvation case.
+
+Additionally, the following line is printed::
+
+	Possible timer handling issue on cpu=4 timer-softirq=11142
+
+Here "cpu" indicates that the grace-period kthread last ran on CPU 4,
+where it queued the fqs timer.  The number following the "timer-softirq"
+is the current ``TIMER_SOFTIRQ`` count on cpu 4.  If this value does not
+change on successive RCU CPU stall warnings, there is further reason to
+suspect a timer problem.
+
 
 Multiple Warnings From One Stall
 ================================

Documentation/RCU/whatisRCU.rst

@@ -683,7 +683,7 @@ Quick Quiz #1:
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 This section presents a "toy" RCU implementation that is based on
 "classic RCU".  It is also short on performance (but only for updates) and
-on features such as hotplug CPU and the ability to run in CONFIG_PREEMPT
+on features such as hotplug CPU and the ability to run in CONFIG_PREEMPTION
 kernels.  The definitions of rcu_dereference() and rcu_assign_pointer()
 are the same as those shown in the preceding section, so they are omitted.
 ::
@@ -739,7 +739,7 @@ Quick Quiz #2:
 Quick Quiz #3:
 		If it is illegal to block in an RCU read-side
 		critical section, what the heck do you do in
-		PREEMPT_RT, where normal spinlocks can block???
+		CONFIG_PREEMPT_RT, where normal spinlocks can block???
 
 :ref:`Answers to Quick Quiz <8_whatisRCU>`
 
@@ -1093,7 +1093,7 @@ Quick Quiz #2:
 		overhead is **negative**.
 
 Answer:
-		Imagine a single-CPU system with a non-CONFIG_PREEMPT
+		Imagine a single-CPU system with a non-CONFIG_PREEMPTION
 		kernel where a routing table is used by process-context
 		code, but can be updated by irq-context code (for example,
 		by an "ICMP REDIRECT" packet).	The usual way of handling
@@ -1120,10 +1120,10 @@ Answer:
 Quick Quiz #3:
 		If it is illegal to block in an RCU read-side
 		critical section, what the heck do you do in
-		PREEMPT_RT, where normal spinlocks can block???
+		CONFIG_PREEMPT_RT, where normal spinlocks can block???
 
 Answer:
-		Just as PREEMPT_RT permits preemption of spinlock
+		Just as CONFIG_PREEMPT_RT permits preemption of spinlock
 		critical sections, it permits preemption of RCU
 		read-side critical sections.  It also permits
 		spinlocks blocking while in RCU read-side critical

Documentation/admin-guide/kernel-parameters.txt

@@ -4078,6 +4078,10 @@
 			value, meaning that RCU_SOFTIRQ is used by default.
 			Specify rcutree.use_softirq=0 to use rcuc kthreads.
 
+			But note that CONFIG_PREEMPT_RT=y kernels disable
+			this kernel boot parameter, forcibly setting it
+			to zero.
+
 	rcutree.rcu_fanout_exact= [KNL]
 			Disable autobalancing of the rcu_node combining
 			tree.  This is used by rcutorture, and might
@@ -4165,12 +4169,6 @@
 			Set wakeup interval for idle CPUs that have
 			RCU callbacks (RCU_FAST_NO_HZ=y).
 
-	rcutree.rcu_idle_lazy_gp_delay= [KNL]
-			Set wakeup interval for idle CPUs that have
-			only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
-			Lazy RCU callbacks are those which RCU can
-			prove do nothing more than free memory.
-
 	rcutree.rcu_kick_kthreads= [KNL]
 			Cause the grace-period kthread to get an extra
 			wake_up() if it sleeps three times longer than
@@ -4324,6 +4322,14 @@
 			stress RCU, they don't participate in the actual
 			test, hence the "fake".
 
+	rcutorture.nocbs_nthreads= [KNL]
+			Set number of RCU callback-offload togglers.
+			Zero (the default) disables toggling.
+
+	rcutorture.nocbs_toggle= [KNL]
+			Set the delay in milliseconds between successive
+			callback-offload toggling attempts.
+
 	rcutorture.nreaders= [KNL]
 			Set number of RCU readers.  The value -1 selects
 			N-1, where N is the number of CPUs.  A value
@@ -4456,6 +4462,13 @@
 			only normal grace-period primitives.  No effect
 			on CONFIG_TINY_RCU kernels.
 
+			But note that CONFIG_PREEMPT_RT=y kernels enables
+			this kernel boot parameter, forcibly setting
+			it to the value one, that is, converting any
+			post-boot attempt at an expedited RCU grace
+			period to instead use normal non-expedited
+			grace-period processing.
+
 	rcupdate.rcu_task_ipi_delay= [KNL]
 			Set time in jiffies during which RCU tasks will
 			avoid sending IPIs, starting with the beginning
@@ -4543,6 +4556,12 @@
 	refscale.verbose= [KNL]
 			Enable additional printk() statements.
 
+	refscale.verbose_batched= [KNL]
+			Batch the additional printk() statements.  If zero
+			(the default) or negative, print everything.  Otherwise,
+			print every Nth verbose statement, where N is the value
+			specified.
+
 	relax_domain_level=
 			[KNL, SMP] Set scheduler's default relax_domain_level.
 			See Documentation/admin-guide/cgroup-v1/cpusets.rst.
@@ -5317,6 +5336,14 @@
 			are running concurrently, especially on systems
 			with rotating-rust storage.
 
+	torture.verbose_sleep_frequency= [KNL]
+			Specifies how many verbose printk()s should be
+			emitted between each sleep.  The default of zero
+			disables verbose-printk() sleeping.
+
+	torture.verbose_sleep_duration= [KNL]
+			Duration of each verbose-printk() sleep in jiffies.
+
 	tp720=		[HW,PS2]
 
 	tpm_suspend_pcr=[HW,TPM]

include/linux/cpu.h

@@ -111,6 +111,8 @@ static inline void cpu_maps_update_done(void)
 #endif /* CONFIG_SMP */
 extern struct bus_type cpu_subsys;
 
+extern int lockdep_is_cpus_held(void);
+
 #ifdef CONFIG_HOTPLUG_CPU
 extern void cpus_write_lock(void);
 extern void cpus_write_unlock(void);

include/linux/list.h

@@ -901,7 +901,7 @@ static inline void hlist_add_before(struct hlist_node *n,
 }
 
 /**
- * hlist_add_behing - add a new entry after the one specified
+ * hlist_add_behind - add a new entry after the one specified
  * @n: new entry to be added
  * @prev: hlist node to add it after, which must be non-NULL
  */

include/linux/mm.h

@@ -3177,5 +3177,7 @@ unsigned long wp_shared_mapping_range(struct address_space *mapping,
 
 extern int sysctl_nr_trim_pages;
 
+void mem_dump_obj(void *object);
+
 #endif /* __KERNEL__ */
 #endif /* _LINUX_MM_H */

include/linux/rcu_segcblist.h

@@ -63,6 +63,122 @@ struct rcu_cblist {
 #define RCU_NEXT_TAIL		3
 #define RCU_CBLIST_NSEGS	4
 
+
+/*
+ *                     ==NOCB Offloading state machine==
+ *
+ *
+ *  ----------------------------------------------------------------------------
+ *  |                         SEGCBLIST_SOFTIRQ_ONLY                           |
+ *  |                                                                          |
+ *  |  Callbacks processed by rcu_core() from softirqs or local                |
+ *  |  rcuc kthread, without holding nocb_lock.                                |
+ *  ----------------------------------------------------------------------------
+ *                                         |
+ *                                         v
+ *  ----------------------------------------------------------------------------
+ *  |                        SEGCBLIST_OFFLOADED                               |
+ *  |                                                                          |
+ *  | Callbacks processed by rcu_core() from softirqs or local                 |
+ *  | rcuc kthread, while holding nocb_lock. Waking up CB and GP kthreads,     |
+ *  | allowing nocb_timer to be armed.                                         |
+ *  ----------------------------------------------------------------------------
+ *                                         |
+ *                                         v
+ *                        -----------------------------------
+ *                        |                                 |
+ *                        v                                 v
+ *  ---------------------------------------  ----------------------------------|
+ *  |        SEGCBLIST_OFFLOADED |        |  |     SEGCBLIST_OFFLOADED |       |
+ *  |        SEGCBLIST_KTHREAD_CB         |  |     SEGCBLIST_KTHREAD_GP        |
+ *  |                                     |  |                                 |
+ *  |                                     |  |                                 |
+ *  | CB kthread woke up and              |  | GP kthread woke up and          |
+ *  | acknowledged SEGCBLIST_OFFLOADED.   |  | acknowledged SEGCBLIST_OFFLOADED|
+ *  | Processes callbacks concurrently    |  |                                 |
+ *  | with rcu_core(), holding            |  |                                 |
+ *  | nocb_lock.                          |  |                                 |
+ *  ---------------------------------------  -----------------------------------
+ *                        |                                 |
+ *                        -----------------------------------
+ *                                         |
+ *                                         v
+ *  |--------------------------------------------------------------------------|
+ *  |                           SEGCBLIST_OFFLOADED |                          |
+ *  |                           SEGCBLIST_KTHREAD_CB |                         |
+ *  |                           SEGCBLIST_KTHREAD_GP                           |
+ *  |                                                                          |
+ *  |   Kthreads handle callbacks holding nocb_lock, local rcu_core() stops    |
+ *  |   handling callbacks.                                                    |
+ *  ----------------------------------------------------------------------------
+ */
+
+
+
+/*
+ *                       ==NOCB De-Offloading state machine==
+ *
+ *
+ *  |--------------------------------------------------------------------------|
+ *  |                           SEGCBLIST_OFFLOADED |                          |
+ *  |                           SEGCBLIST_KTHREAD_CB |                         |
+ *  |                           SEGCBLIST_KTHREAD_GP                           |
+ *  |                                                                          |
+ *  |   CB/GP kthreads handle callbacks holding nocb_lock, local rcu_core()    |
+ *  |   ignores callbacks.                                                     |
+ *  ----------------------------------------------------------------------------
+ *                                      |
+ *                                      v
+ *  |--------------------------------------------------------------------------|
+ *  |                           SEGCBLIST_KTHREAD_CB |                         |
+ *  |                           SEGCBLIST_KTHREAD_GP                           |
+ *  |                                                                          |
+ *  |   CB/GP kthreads and local rcu_core() handle callbacks concurrently      |
+ *  |   holding nocb_lock. Wake up CB and GP kthreads if necessary.            |
+ *  ----------------------------------------------------------------------------
+ *                                      |
+ *                                      v
+ *                     -----------------------------------
+ *                     |                                 |
+ *                     v                                 v
+ *  ---------------------------------------------------------------------------|
+ *  |                                                                          |
+ *  |        SEGCBLIST_KTHREAD_CB         |       SEGCBLIST_KTHREAD_GP         |
+ *  |                                     |                                    |
+ *  | GP kthread woke up and              |   CB kthread woke up and           |
+ *  | acknowledged the fact that          |   acknowledged the fact that       |
+ *  | SEGCBLIST_OFFLOADED got cleared.    |   SEGCBLIST_OFFLOADED got cleared. |
+ *  |                                     |   The CB kthread goes to sleep     |
+ *  | The callbacks from the target CPU   |   until it ever gets re-offloaded. |
+ *  | will be ignored from the GP kthread |                                    |
+ *  | loop.                               |                                    |
+ *  ----------------------------------------------------------------------------
+ *                      |                                 |
+ *                      -----------------------------------
+ *                                      |
+ *                                      v
+ *  ----------------------------------------------------------------------------
+ *  |                                   0                                      |
+ *  |                                                                          |
+ *  | Callbacks processed by rcu_core() from softirqs or local                 |
+ *  | rcuc kthread, while holding nocb_lock. Forbid nocb_timer to be armed.    |
+ *  | Flush pending nocb_timer. Flush nocb bypass callbacks.                   |
+ *  ----------------------------------------------------------------------------
+ *                                      |
+ *                                      v
+ *  ----------------------------------------------------------------------------
+ *  |                         SEGCBLIST_SOFTIRQ_ONLY                           |
+ *  |                                                                          |
+ *  |  Callbacks processed by rcu_core() from softirqs or local                |
+ *  |  rcuc kthread, without holding nocb_lock.                                |
+ *  ----------------------------------------------------------------------------
+ */
+#define SEGCBLIST_ENABLED	BIT(0)
+#define SEGCBLIST_SOFTIRQ_ONLY	BIT(1)
+#define SEGCBLIST_KTHREAD_CB	BIT(2)
+#define SEGCBLIST_KTHREAD_GP	BIT(3)
+#define SEGCBLIST_OFFLOADED	BIT(4)
+
 struct rcu_segcblist {
 	struct rcu_head *head;
 	struct rcu_head **tails[RCU_CBLIST_NSEGS];
@@ -72,8 +188,8 @@ struct rcu_segcblist {
 #else
 	long len;
 #endif
-	u8 enabled;
-	u8 offloaded;
+	long seglen[RCU_CBLIST_NSEGS];
+	u8 flags;
 };
 
 #define RCU_SEGCBLIST_INITIALIZER(n) \

include/linux/rcupdate.h

@@ -33,6 +33,8 @@
 #define ULONG_CMP_GE(a, b)	(ULONG_MAX / 2 >= (a) - (b))
 #define ULONG_CMP_LT(a, b)	(ULONG_MAX / 2 < (a) - (b))
 #define ulong2long(a)		(*(long *)(&(a)))
+#define USHORT_CMP_GE(a, b)	(USHRT_MAX / 2 >= (unsigned short)((a) - (b)))
+#define USHORT_CMP_LT(a, b)	(USHRT_MAX / 2 < (unsigned short)((a) - (b)))
 
 /* Exported common interfaces */
 void call_rcu(struct rcu_head *head, rcu_callback_t func);
@@ -110,8 +112,12 @@ static inline void rcu_user_exit(void) { }
 
 #ifdef CONFIG_RCU_NOCB_CPU
 void rcu_init_nohz(void);
+int rcu_nocb_cpu_offload(int cpu);
+int rcu_nocb_cpu_deoffload(int cpu);
 #else /* #ifdef CONFIG_RCU_NOCB_CPU */
 static inline void rcu_init_nohz(void) { }
+static inline int rcu_nocb_cpu_offload(int cpu) { return -EINVAL; }
+static inline int rcu_nocb_cpu_deoffload(int cpu) { return 0; }
 #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
 
 /**
@@ -846,19 +852,11 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
  */
 #define __is_kvfree_rcu_offset(offset) ((offset) < 4096)
 
-/*
- * Helper macro for kfree_rcu() to prevent argument-expansion eyestrain.
- */
-#define __kvfree_rcu(head, offset) \
-	do { \
-		BUILD_BUG_ON(!__is_kvfree_rcu_offset(offset)); \
-		kvfree_call_rcu(head, (rcu_callback_t)(unsigned long)(offset)); \
-	} while (0)
-
 /**
  * kfree_rcu() - kfree an object after a grace period.
- * @ptr:	pointer to kfree
- * @rhf:	the name of the struct rcu_head within the type of @ptr.
+ * @ptr: pointer to kfree for both single- and double-argument invocations.
+ * @rhf: the name of the struct rcu_head within the type of @ptr,
+ *       but only for double-argument invocations.
  *
  * Many rcu callbacks functions just call kfree() on the base structure.
  * These functions are trivial, but their size adds up, and furthermore
@@ -871,7 +869,7 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
  * Because the functions are not allowed in the low-order 4096 bytes of
  * kernel virtual memory, offsets up to 4095 bytes can be accommodated.
  * If the offset is larger than 4095 bytes, a compile-time error will
- * be generated in __kvfree_rcu(). If this error is triggered, you can
+ * be generated in kvfree_rcu_arg_2(). If this error is triggered, you can
  * either fall back to use of call_rcu() or rearrange the structure to
  * position the rcu_head structure into the first 4096 bytes.
  *
@@ -881,13 +879,7 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
  * The BUILD_BUG_ON check must not involve any function calls, hence the
  * checks are done in macros here.
  */
-#define kfree_rcu(ptr, rhf)						\
-do {									\
-	typeof (ptr) ___p = (ptr);					\
-									\
-	if (___p)							\
-		__kvfree_rcu(&((___p)->rhf), offsetof(typeof(*(ptr)), rhf)); \
-} while (0)
+#define kfree_rcu kvfree_rcu
 
 /**
  * kvfree_rcu() - kvfree an object after a grace period.
@@ -919,7 +911,17 @@ do {									\
 	kvfree_rcu_arg_2, kvfree_rcu_arg_1)(__VA_ARGS__)
 
 #define KVFREE_GET_MACRO(_1, _2, NAME, ...) NAME
-#define kvfree_rcu_arg_2(ptr, rhf) kfree_rcu(ptr, rhf)
+#define kvfree_rcu_arg_2(ptr, rhf)					\
+do {									\
+	typeof (ptr) ___p = (ptr);					\
+									\
+	if (___p) {									\
+		BUILD_BUG_ON(!__is_kvfree_rcu_offset(offsetof(typeof(*(ptr)), rhf)));	\
+		kvfree_call_rcu(&((___p)->rhf), (rcu_callback_t)(unsigned long)		\
+			(offsetof(typeof(*(ptr)), rhf)));				\
+	}										\
+} while (0)
+
 #define kvfree_rcu_arg_1(ptr)					\
 do {								\
 	typeof(ptr) ___p = (ptr);				\

include/linux/slab.h

@@ -186,6 +186,8 @@ void kfree(const void *);
 void kfree_sensitive(const void *);
 size_t __ksize(const void *);
 size_t ksize(const void *);
+bool kmem_valid_obj(void *object);
+void kmem_dump_obj(void *object);
 
 #ifdef CONFIG_HAVE_HARDENED_USERCOPY_ALLOCATOR
 void __check_heap_object(const void *ptr, unsigned long n, struct page *page,

include/linux/srcu.h

@@ -60,6 +60,9 @@ void cleanup_srcu_struct(struct srcu_struct *ssp);
 int __srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp);
 void __srcu_read_unlock(struct srcu_struct *ssp, int idx) __releases(ssp);
 void synchronize_srcu(struct srcu_struct *ssp);
+unsigned long get_state_synchronize_srcu(struct srcu_struct *ssp);
+unsigned long start_poll_synchronize_srcu(struct srcu_struct *ssp);
+bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie);
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 

include/linux/srcutiny.h

@@ -15,7 +15,8 @@
 
 struct srcu_struct {
 	short srcu_lock_nesting[2];	/* srcu_read_lock() nesting depth. */
-	short srcu_idx;			/* Current reader array element. */
+	unsigned short srcu_idx;	/* Current reader array element in bit 0x2. */
+	unsigned short srcu_idx_max;	/* Furthest future srcu_idx request. */
 	u8 srcu_gp_running;		/* GP workqueue running? */
 	u8 srcu_gp_waiting;		/* GP waiting for readers? */
 	struct swait_queue_head srcu_wq;
@@ -59,7 +60,7 @@ static inline int __srcu_read_lock(struct srcu_struct *ssp)
 {
 	int idx;
 
-	idx = READ_ONCE(ssp->srcu_idx);
+	idx = ((READ_ONCE(ssp->srcu_idx) + 1) & 0x2) >> 1;
 	WRITE_ONCE(ssp->srcu_lock_nesting[idx], ssp->srcu_lock_nesting[idx] + 1);
 	return idx;
 }
@@ -80,7 +81,7 @@ static inline void srcu_torture_stats_print(struct srcu_struct *ssp,
 {
 	int idx;
 
-	idx = READ_ONCE(ssp->srcu_idx) & 0x1;
+	idx = ((READ_ONCE(ssp->srcu_idx) + 1) & 0x2) >> 1;
 	pr_alert("%s%s Tiny SRCU per-CPU(idx=%d): (%hd,%hd)\n",
 		 tt, tf, idx,
 		 READ_ONCE(ssp->srcu_lock_nesting[!idx]),

include/linux/timer.h

@@ -192,6 +192,8 @@ extern int try_to_del_timer_sync(struct timer_list *timer);
 
 #define del_singleshot_timer_sync(t) del_timer_sync(t)
 
+extern bool timer_curr_running(struct timer_list *timer);
+
 extern void init_timers(void);
 struct hrtimer;
 extern enum hrtimer_restart it_real_fn(struct hrtimer *);

include/linux/torture.h

@@ -32,11 +32,27 @@
 #define TOROUT_STRING(s) \
 	pr_alert("%s" TORTURE_FLAG " %s\n", torture_type, s)
 #define VERBOSE_TOROUT_STRING(s) \
-	do { if (verbose) pr_alert("%s" TORTURE_FLAG " %s\n", torture_type, s); } while (0)
+do {										\
+	if (verbose) {								\
+		verbose_torout_sleep();						\
+		pr_alert("%s" TORTURE_FLAG " %s\n", torture_type, s);		\
+	}									\
+} while (0)
 #define VERBOSE_TOROUT_ERRSTRING(s) \
-	do { if (verbose) pr_alert("%s" TORTURE_FLAG "!!! %s\n", torture_type, s); } while (0)
+do {										\
+	if (verbose) {								\
+		verbose_torout_sleep();						\
+		pr_alert("%s" TORTURE_FLAG "!!! %s\n", torture_type, s);	\
+	}									\
+} while (0)
+void verbose_torout_sleep(void);
 
 /* Definitions for online/offline exerciser. */
+#ifdef CONFIG_HOTPLUG_CPU
+int torture_num_online_cpus(void);
+#else /* #ifdef CONFIG_HOTPLUG_CPU */
+static inline int torture_num_online_cpus(void) { return 1; }
+#endif /* #else #ifdef CONFIG_HOTPLUG_CPU */
 typedef void torture_ofl_func(void);
 bool torture_offline(int cpu, long *n_onl_attempts, long *n_onl_successes,
 		     unsigned long *sum_offl, int *min_onl, int *max_onl);
@@ -61,6 +77,13 @@ static inline void torture_random_init(struct torture_random_state *trsp)
 	trsp->trs_count = 0;
 }
 
+/* Definitions for high-resolution-timer sleeps. */
+int torture_hrtimeout_ns(ktime_t baset_ns, u32 fuzzt_ns, struct torture_random_state *trsp);
+int torture_hrtimeout_us(u32 baset_us, u32 fuzzt_ns, struct torture_random_state *trsp);
+int torture_hrtimeout_ms(u32 baset_ms, u32 fuzzt_us, struct torture_random_state *trsp);
+int torture_hrtimeout_jiffies(u32 baset_j, struct torture_random_state *trsp);
+int torture_hrtimeout_s(u32 baset_s, u32 fuzzt_ms, struct torture_random_state *trsp);
+
 /* Task shuffler, which causes CPUs to occasionally go idle. */
 void torture_shuffle_task_register(struct task_struct *tp);
 int torture_shuffle_init(long shuffint);

include/linux/vmalloc.h

@@ -241,4 +241,10 @@ pcpu_free_vm_areas(struct vm_struct **vms, int nr_vms)
 int register_vmap_purge_notifier(struct notifier_block *nb);
 int unregister_vmap_purge_notifier(struct notifier_block *nb);
 
+#ifdef CONFIG_MMU
+bool vmalloc_dump_obj(void *object);
+#else
+static inline bool vmalloc_dump_obj(void *object) { return false; }
+#endif
+
 #endif /* _LINUX_VMALLOC_H */

include/trace/events/rcu.h

@@ -505,6 +505,32 @@ TRACE_EVENT_RCU(rcu_callback,
 		  __entry->qlen)
 );
 
+TRACE_EVENT_RCU(rcu_segcb_stats,
+
+		TP_PROTO(struct rcu_segcblist *rs, const char *ctx),
+
+		TP_ARGS(rs, ctx),
+
+		TP_STRUCT__entry(
+			__field(const char *, ctx)
+			__array(unsigned long, gp_seq, RCU_CBLIST_NSEGS)
+			__array(long, seglen, RCU_CBLIST_NSEGS)
+		),
+
+		TP_fast_assign(
+			__entry->ctx = ctx;
+			memcpy(__entry->seglen, rs->seglen, RCU_CBLIST_NSEGS * sizeof(long));
+			memcpy(__entry->gp_seq, rs->gp_seq, RCU_CBLIST_NSEGS * sizeof(unsigned long));
+
+		),
+
+		TP_printk("%s seglen: (DONE=%ld, WAIT=%ld, NEXT_READY=%ld, NEXT=%ld) "
+			  "gp_seq: (DONE=%lu, WAIT=%lu, NEXT_READY=%lu, NEXT=%lu)", __entry->ctx,
+			  __entry->seglen[0], __entry->seglen[1], __entry->seglen[2], __entry->seglen[3],
+			  __entry->gp_seq[0], __entry->gp_seq[1], __entry->gp_seq[2], __entry->gp_seq[3])
+
+);
+
 /*
  * Tracepoint for the registration of a single RCU callback of the special
  * kvfree() form.  The first argument is the RCU type, the second argument

kernel/cpu.c

@@ -330,6 +330,13 @@ void lockdep_assert_cpus_held(void)
 	percpu_rwsem_assert_held(&cpu_hotplug_lock);
 }
 
+#ifdef CONFIG_LOCKDEP
+int lockdep_is_cpus_held(void)
+{
+	return percpu_rwsem_is_held(&cpu_hotplug_lock);
+}
+#endif
+
 static void lockdep_acquire_cpus_lock(void)
 {
 	rwsem_acquire(&cpu_hotplug_lock.dep_map, 0, 0, _THIS_IP_);

kernel/locking/locktorture.c

@@ -27,7 +27,6 @@
 #include <linux/moduleparam.h>
 #include <linux/delay.h>
 #include <linux/slab.h>
-#include <linux/percpu-rwsem.h>
 #include <linux/torture.h>
 #include <linux/reboot.h>
 

kernel/rcu/Kconfig

@@ -95,6 +95,7 @@ config TASKS_RUDE_RCU
 
 config TASKS_TRACE_RCU
 	def_bool 0
+	select IRQ_WORK
 	help
 	  This option enables a task-based RCU implementation that uses
 	  explicit rcu_read_lock_trace() read-side markers, and allows
@@ -188,8 +189,8 @@ config RCU_FAST_NO_HZ
 
 config RCU_BOOST
 	bool "Enable RCU priority boosting"
-	depends on RT_MUTEXES && PREEMPT_RCU && RCU_EXPERT
-	default n
+	depends on (RT_MUTEXES && PREEMPT_RCU && RCU_EXPERT) || PREEMPT_RT
+	default y if PREEMPT_RT
 	help
 	  This option boosts the priority of preempted RCU readers that
 	  block the current preemptible RCU grace period for too long.

kernel/rcu/rcu.h

@@ -378,7 +378,11 @@ do {									\
 	smp_mb__after_unlock_lock();					\
 } while (0)
 
-#define raw_spin_unlock_rcu_node(p) raw_spin_unlock(&ACCESS_PRIVATE(p, lock))
+#define raw_spin_unlock_rcu_node(p)					\
+do {									\
+	lockdep_assert_irqs_disabled();					\
+	raw_spin_unlock(&ACCESS_PRIVATE(p, lock));			\
+} while (0)
 
 #define raw_spin_lock_irq_rcu_node(p)					\
 do {									\
@@ -387,7 +391,10 @@ do {									\
 } while (0)
 
 #define raw_spin_unlock_irq_rcu_node(p)					\
-	raw_spin_unlock_irq(&ACCESS_PRIVATE(p, lock))
+do {									\
+	lockdep_assert_irqs_disabled();					\
+	raw_spin_unlock_irq(&ACCESS_PRIVATE(p, lock));			\
+} while (0)
 
 #define raw_spin_lock_irqsave_rcu_node(p, flags)			\
 do {									\
@@ -396,7 +403,10 @@ do {									\
 } while (0)
 
 #define raw_spin_unlock_irqrestore_rcu_node(p, flags)			\
-	raw_spin_unlock_irqrestore(&ACCESS_PRIVATE(p, lock), flags)
+do {									\
+	lockdep_assert_irqs_disabled();					\
+	raw_spin_unlock_irqrestore(&ACCESS_PRIVATE(p, lock), flags);	\
+} while (0)
 
 #define raw_spin_trylock_rcu_node(p)					\
 ({									\

kernel/rcu/rcu_segcblist.h

@@ -15,6 +15,9 @@ static inline long rcu_cblist_n_cbs(struct rcu_cblist *rclp)
 	return READ_ONCE(rclp->len);
 }
 
+/* Return number of callbacks in segmented callback list by summing seglen. */
+long rcu_segcblist_n_segment_cbs(struct rcu_segcblist *rsclp);
+
 void rcu_cblist_init(struct rcu_cblist *rclp);
 void rcu_cblist_enqueue(struct rcu_cblist *rclp, struct rcu_head *rhp);
 void rcu_cblist_flush_enqueue(struct rcu_cblist *drclp,
@@ -50,19 +53,51 @@ static inline long rcu_segcblist_n_cbs(struct rcu_segcblist *rsclp)
 #endif
 }
 
+static inline void rcu_segcblist_set_flags(struct rcu_segcblist *rsclp,
+					   int flags)
+{
+	rsclp->flags |= flags;
+}
+
+static inline void rcu_segcblist_clear_flags(struct rcu_segcblist *rsclp,
+					     int flags)
+{
+	rsclp->flags &= ~flags;
+}
+
+static inline bool rcu_segcblist_test_flags(struct rcu_segcblist *rsclp,
+					    int flags)
+{
+	return READ_ONCE(rsclp->flags) & flags;
+}
+
 /*
  * Is the specified rcu_segcblist enabled, for example, not corresponding
  * to an offline CPU?
  */
 static inline bool rcu_segcblist_is_enabled(struct rcu_segcblist *rsclp)
 {
-	return rsclp->enabled;
+	return rcu_segcblist_test_flags(rsclp, SEGCBLIST_ENABLED);
 }
 
-/* Is the specified rcu_segcblist offloaded?  */
+/* Is the specified rcu_segcblist offloaded, or is SEGCBLIST_SOFTIRQ_ONLY set? */
 static inline bool rcu_segcblist_is_offloaded(struct rcu_segcblist *rsclp)
 {
-	return IS_ENABLED(CONFIG_RCU_NOCB_CPU) && rsclp->offloaded;
+	if (IS_ENABLED(CONFIG_RCU_NOCB_CPU) &&
+	    !rcu_segcblist_test_flags(rsclp, SEGCBLIST_SOFTIRQ_ONLY))
+		return true;
+
+	return false;
+}
+
+static inline bool rcu_segcblist_completely_offloaded(struct rcu_segcblist *rsclp)
+{
+	int flags = SEGCBLIST_KTHREAD_CB | SEGCBLIST_KTHREAD_GP | SEGCBLIST_OFFLOADED;
+
+	if (IS_ENABLED(CONFIG_RCU_NOCB_CPU) && (rsclp->flags & flags) == flags)
+		return true;
+
+	return false;
 }
 
 /*
@@ -75,10 +110,22 @@ static inline bool rcu_segcblist_restempty(struct rcu_segcblist *rsclp, int seg)
 	return !READ_ONCE(*READ_ONCE(rsclp->tails[seg]));
 }
 
+/*
+ * Is the specified segment of the specified rcu_segcblist structure
+ * empty of callbacks?
+ */
+static inline bool rcu_segcblist_segempty(struct rcu_segcblist *rsclp, int seg)
+{
+	if (seg == RCU_DONE_TAIL)
+		return &rsclp->head == rsclp->tails[RCU_DONE_TAIL];
+	return rsclp->tails[seg - 1] == rsclp->tails[seg];
+}
+
 void rcu_segcblist_inc_len(struct rcu_segcblist *rsclp);
+void rcu_segcblist_add_len(struct rcu_segcblist *rsclp, long v);
 void rcu_segcblist_init(struct rcu_segcblist *rsclp);
 void rcu_segcblist_disable(struct rcu_segcblist *rsclp);
-void rcu_segcblist_offload(struct rcu_segcblist *rsclp);
+void rcu_segcblist_offload(struct rcu_segcblist *rsclp, bool offload);
 bool rcu_segcblist_ready_cbs(struct rcu_segcblist *rsclp);
 bool rcu_segcblist_pend_cbs(struct rcu_segcblist *rsclp);
 struct rcu_head *rcu_segcblist_first_cb(struct rcu_segcblist *rsclp);
@@ -88,8 +135,6 @@ void rcu_segcblist_enqueue(struct rcu_segcblist *rsclp,
 			   struct rcu_head *rhp);
 bool rcu_segcblist_entrain(struct rcu_segcblist *rsclp,
 			   struct rcu_head *rhp);
-void rcu_segcblist_extract_count(struct rcu_segcblist *rsclp,
-				 struct rcu_cblist *rclp);
 void rcu_segcblist_extract_done_cbs(struct rcu_segcblist *rsclp,
 				    struct rcu_cblist *rclp);
 void rcu_segcblist_extract_pend_cbs(struct rcu_segcblist *rsclp,

kernel/rcu/refscale.c

@@ -46,6 +46,18 @@
 #define VERBOSE_SCALEOUT(s, x...) \
 	do { if (verbose) pr_alert("%s" SCALE_FLAG s, scale_type, ## x); } while (0)
 
+static atomic_t verbose_batch_ctr;
+
+#define VERBOSE_SCALEOUT_BATCH(s, x...)							\
+do {											\
+	if (verbose &&									\
+	    (verbose_batched <= 0 ||							\
+	     !(atomic_inc_return(&verbose_batch_ctr) % verbose_batched))) {		\
+		schedule_timeout_uninterruptible(1);					\
+		pr_alert("%s" SCALE_FLAG s, scale_type, ## x);				\
+	}										\
+} while (0)
+
 #define VERBOSE_SCALEOUT_ERRSTRING(s, x...) \
 	do { if (verbose) pr_alert("%s" SCALE_FLAG "!!! " s, scale_type, ## x); } while (0)
 
@@ -57,6 +69,7 @@ module_param(scale_type, charp, 0444);
 MODULE_PARM_DESC(scale_type, "Type of test (rcu, srcu, refcnt, rwsem, rwlock.");
 
 torture_param(int, verbose, 0, "Enable verbose debugging printk()s");
+torture_param(int, verbose_batched, 0, "Batch verbose debugging printk()s");
 
 // Wait until there are multiple CPUs before starting test.
 torture_param(int, holdoff, IS_BUILTIN(CONFIG_RCU_REF_SCALE_TEST) ? 10 : 0,
@@ -368,14 +381,14 @@ ref_scale_reader(void *arg)
 	u64 start;
 	s64 duration;
 
-	VERBOSE_SCALEOUT("ref_scale_reader %ld: task started", me);
+	VERBOSE_SCALEOUT_BATCH("ref_scale_reader %ld: task started", me);
 	set_cpus_allowed_ptr(current, cpumask_of(me % nr_cpu_ids));
 	set_user_nice(current, MAX_NICE);
 	atomic_inc(&n_init);
 	if (holdoff)
 		schedule_timeout_interruptible(holdoff * HZ);
 repeat:
-	VERBOSE_SCALEOUT("ref_scale_reader %ld: waiting to start next experiment on cpu %d", me, smp_processor_id());
+	VERBOSE_SCALEOUT_BATCH("ref_scale_reader %ld: waiting to start next experiment on cpu %d", me, smp_processor_id());
 
 	// Wait for signal that this reader can start.
 	wait_event(rt->wq, (atomic_read(&nreaders_exp) && smp_load_acquire(&rt->start_reader)) ||
@@ -392,7 +405,7 @@ ref_scale_reader(void *arg)
 		while (atomic_read_acquire(&n_started))
 			cpu_relax();
 
-	VERBOSE_SCALEOUT("ref_scale_reader %ld: experiment %d started", me, exp_idx);
+	VERBOSE_SCALEOUT_BATCH("ref_scale_reader %ld: experiment %d started", me, exp_idx);
 
 
 	// To reduce noise, do an initial cache-warming invocation, check
@@ -421,7 +434,7 @@ ref_scale_reader(void *arg)
 	if (atomic_dec_and_test(&nreaders_exp))
 		wake_up(&main_wq);
 
-	VERBOSE_SCALEOUT("ref_scale_reader %ld: experiment %d ended, (readers remaining=%d)",
+	VERBOSE_SCALEOUT_BATCH("ref_scale_reader %ld: experiment %d ended, (readers remaining=%d)",
 				me, exp_idx, atomic_read(&nreaders_exp));
 
 	if (!torture_must_stop())

kernel/rcu/srcutiny.c

@@ -34,6 +34,7 @@ static int init_srcu_struct_fields(struct srcu_struct *ssp)
 	ssp->srcu_gp_running = false;
 	ssp->srcu_gp_waiting = false;
 	ssp->srcu_idx = 0;
+	ssp->srcu_idx_max = 0;
 	INIT_WORK(&ssp->srcu_work, srcu_drive_gp);
 	INIT_LIST_HEAD(&ssp->srcu_work.entry);
 	return 0;
@@ -84,6 +85,8 @@ void cleanup_srcu_struct(struct srcu_struct *ssp)
 	WARN_ON(ssp->srcu_gp_waiting);
 	WARN_ON(ssp->srcu_cb_head);
 	WARN_ON(&ssp->srcu_cb_head != ssp->srcu_cb_tail);
+	WARN_ON(ssp->srcu_idx != ssp->srcu_idx_max);
+	WARN_ON(ssp->srcu_idx & 0x1);
 }
 EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
 
@@ -114,7 +117,7 @@ void srcu_drive_gp(struct work_struct *wp)
 	struct srcu_struct *ssp;
 
 	ssp = container_of(wp, struct srcu_struct, srcu_work);
-	if (ssp->srcu_gp_running || !READ_ONCE(ssp->srcu_cb_head))
+	if (ssp->srcu_gp_running || USHORT_CMP_GE(ssp->srcu_idx, READ_ONCE(ssp->srcu_idx_max)))
 		return; /* Already running or nothing to do. */
 
 	/* Remove recently arrived callbacks and wait for readers. */
@@ -124,11 +127,12 @@ void srcu_drive_gp(struct work_struct *wp)
 	ssp->srcu_cb_head = NULL;
 	ssp->srcu_cb_tail = &ssp->srcu_cb_head;
 	local_irq_enable();
-	idx = ssp->srcu_idx;
-	WRITE_ONCE(ssp->srcu_idx, !ssp->srcu_idx);
+	idx = (ssp->srcu_idx & 0x2) / 2;
+	WRITE_ONCE(ssp->srcu_idx, ssp->srcu_idx + 1);
 	WRITE_ONCE(ssp->srcu_gp_waiting, true);  /* srcu_read_unlock() wakes! */
 	swait_event_exclusive(ssp->srcu_wq, !READ_ONCE(ssp->srcu_lock_nesting[idx]));
 	WRITE_ONCE(ssp->srcu_gp_waiting, false); /* srcu_read_unlock() cheap. */
+	WRITE_ONCE(ssp->srcu_idx, ssp->srcu_idx + 1);
 
 	/* Invoke the callbacks we removed above. */
 	while (lh) {
@@ -146,11 +150,27 @@ void srcu_drive_gp(struct work_struct *wp)
 	 * straighten that out.
 	 */
 	WRITE_ONCE(ssp->srcu_gp_running, false);
-	if (READ_ONCE(ssp->srcu_cb_head))
+	if (USHORT_CMP_LT(ssp->srcu_idx, READ_ONCE(ssp->srcu_idx_max)))
 		schedule_work(&ssp->srcu_work);
 }
 EXPORT_SYMBOL_GPL(srcu_drive_gp);
 
+static void srcu_gp_start_if_needed(struct srcu_struct *ssp)
+{
+	unsigned short cookie;
+
+	cookie = get_state_synchronize_srcu(ssp);
+	if (USHORT_CMP_GE(READ_ONCE(ssp->srcu_idx_max), cookie))
+		return;
+	WRITE_ONCE(ssp->srcu_idx_max, cookie);
+	if (!READ_ONCE(ssp->srcu_gp_running)) {
+		if (likely(srcu_init_done))
+			schedule_work(&ssp->srcu_work);
+		else if (list_empty(&ssp->srcu_work.entry))
+			list_add(&ssp->srcu_work.entry, &srcu_boot_list);
+	}
+}
+
 /*
  * Enqueue an SRCU callback on the specified srcu_struct structure,
  * initiating grace-period processing if it is not already running.
@@ -166,12 +186,7 @@ void call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
 	*ssp->srcu_cb_tail = rhp;
 	ssp->srcu_cb_tail = &rhp->next;
 	local_irq_restore(flags);
-	if (!READ_ONCE(ssp->srcu_gp_running)) {
-		if (likely(srcu_init_done))
-			schedule_work(&ssp->srcu_work);
-		else if (list_empty(&ssp->srcu_work.entry))
-			list_add(&ssp->srcu_work.entry, &srcu_boot_list);
-	}
+	srcu_gp_start_if_needed(ssp);
 }
 EXPORT_SYMBOL_GPL(call_srcu);
 
@@ -190,6 +205,48 @@ void synchronize_srcu(struct srcu_struct *ssp)
 }
 EXPORT_SYMBOL_GPL(synchronize_srcu);
 
+/*
+ * get_state_synchronize_srcu - Provide an end-of-grace-period cookie
+ */
+unsigned long get_state_synchronize_srcu(struct srcu_struct *ssp)
+{
+	unsigned long ret;
+
+	barrier();
+	ret = (READ_ONCE(ssp->srcu_idx) + 3) & ~0x1;
+	barrier();
+	return ret & USHRT_MAX;
+}
+EXPORT_SYMBOL_GPL(get_state_synchronize_srcu);
+
+/*
+ * start_poll_synchronize_srcu - Provide cookie and start grace period
+ *
+ * The difference between this and get_state_synchronize_srcu() is that
+ * this function ensures that the poll_state_synchronize_srcu() will
+ * eventually return the value true.
+ */
+unsigned long start_poll_synchronize_srcu(struct srcu_struct *ssp)
+{
+	unsigned long ret = get_state_synchronize_srcu(ssp);
+
+	srcu_gp_start_if_needed(ssp);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(start_poll_synchronize_srcu);
+
+/*
+ * poll_state_synchronize_srcu - Has cookie's grace period ended?
+ */
+bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie)
+{
+	bool ret = USHORT_CMP_GE(READ_ONCE(ssp->srcu_idx), cookie);
+
+	barrier();
+	return ret;
+}
+EXPORT_SYMBOL_GPL(poll_state_synchronize_srcu);
+
 /* Lockdep diagnostics.  */
 void __init rcu_scheduler_starting(void)
 {

kernel/rcu/srcutree.c

@@ -807,6 +807,46 @@ static void srcu_leak_callback(struct rcu_head *rhp)
 {
 }
 
+/*
+ * Start an SRCU grace period, and also queue the callback if non-NULL.
+ */
+static unsigned long srcu_gp_start_if_needed(struct srcu_struct *ssp,
+					     struct rcu_head *rhp, bool do_norm)
+{
+	unsigned long flags;
+	int idx;
+	bool needexp = false;
+	bool needgp = false;
+	unsigned long s;
+	struct srcu_data *sdp;
+
+	check_init_srcu_struct(ssp);
+	idx = srcu_read_lock(ssp);
+	sdp = raw_cpu_ptr(ssp->sda);
+	spin_lock_irqsave_rcu_node(sdp, flags);
+	if (rhp)
+		rcu_segcblist_enqueue(&sdp->srcu_cblist, rhp);
+	rcu_segcblist_advance(&sdp->srcu_cblist,
+			      rcu_seq_current(&ssp->srcu_gp_seq));
+	s = rcu_seq_snap(&ssp->srcu_gp_seq);
+	(void)rcu_segcblist_accelerate(&sdp->srcu_cblist, s);
+	if (ULONG_CMP_LT(sdp->srcu_gp_seq_needed, s)) {
+		sdp->srcu_gp_seq_needed = s;
+		needgp = true;
+	}
+	if (!do_norm && ULONG_CMP_LT(sdp->srcu_gp_seq_needed_exp, s)) {
+		sdp->srcu_gp_seq_needed_exp = s;
+		needexp = true;
+	}
+	spin_unlock_irqrestore_rcu_node(sdp, flags);
+	if (needgp)
+		srcu_funnel_gp_start(ssp, sdp, s, do_norm);
+	else if (needexp)
+		srcu_funnel_exp_start(ssp, sdp->mynode, s);
+	srcu_read_unlock(ssp, idx);
+	return s;
+}
+
 /*
  * Enqueue an SRCU callback on the srcu_data structure associated with
  * the current CPU and the specified srcu_struct structure, initiating
@@ -838,14 +878,6 @@ static void srcu_leak_callback(struct rcu_head *rhp)
 static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
 			rcu_callback_t func, bool do_norm)
 {
-	unsigned long flags;
-	int idx;
-	bool needexp = false;
-	bool needgp = false;
-	unsigned long s;
-	struct srcu_data *sdp;
-
-	check_init_srcu_struct(ssp);
 	if (debug_rcu_head_queue(rhp)) {
 		/* Probable double call_srcu(), so leak the callback. */
 		WRITE_ONCE(rhp->func, srcu_leak_callback);
@@ -853,28 +885,7 @@ static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
 		return;
 	}
 	rhp->func = func;
-	idx = srcu_read_lock(ssp);
-	sdp = raw_cpu_ptr(ssp->sda);
-	spin_lock_irqsave_rcu_node(sdp, flags);
-	rcu_segcblist_enqueue(&sdp->srcu_cblist, rhp);
-	rcu_segcblist_advance(&sdp->srcu_cblist,
-			      rcu_seq_current(&ssp->srcu_gp_seq));
-	s = rcu_seq_snap(&ssp->srcu_gp_seq);
-	(void)rcu_segcblist_accelerate(&sdp->srcu_cblist, s);
-	if (ULONG_CMP_LT(sdp->srcu_gp_seq_needed, s)) {
-		sdp->srcu_gp_seq_needed = s;
-		needgp = true;
-	}
-	if (!do_norm && ULONG_CMP_LT(sdp->srcu_gp_seq_needed_exp, s)) {
-		sdp->srcu_gp_seq_needed_exp = s;
-		needexp = true;
-	}
-	spin_unlock_irqrestore_rcu_node(sdp, flags);
-	if (needgp)
-		srcu_funnel_gp_start(ssp, sdp, s, do_norm);
-	else if (needexp)
-		srcu_funnel_exp_start(ssp, sdp->mynode, s);
-	srcu_read_unlock(ssp, idx);
+	(void)srcu_gp_start_if_needed(ssp, rhp, do_norm);
 }
 
 /**
@@ -1003,6 +1014,77 @@ void synchronize_srcu(struct srcu_struct *ssp)
 }
 EXPORT_SYMBOL_GPL(synchronize_srcu);
 
+/**
+ * get_state_synchronize_srcu - Provide an end-of-grace-period cookie
+ * @ssp: srcu_struct to provide cookie for.
+ *
+ * This function returns a cookie that can be passed to
+ * poll_state_synchronize_srcu(), which will return true if a full grace
+ * period has elapsed in the meantime.  It is the caller's responsibility
+ * to make sure that grace period happens, for example, by invoking
+ * call_srcu() after return from get_state_synchronize_srcu().
+ */
+unsigned long get_state_synchronize_srcu(struct srcu_struct *ssp)
+{
+	// Any prior manipulation of SRCU-protected data must happen
+	// before the load from ->srcu_gp_seq.
+	smp_mb();
+	return rcu_seq_snap(&ssp->srcu_gp_seq);
+}
+EXPORT_SYMBOL_GPL(get_state_synchronize_srcu);
+
+/**
+ * start_poll_synchronize_srcu - Provide cookie and start grace period
+ * @ssp: srcu_struct to provide cookie for.
+ *
+ * This function returns a cookie that can be passed to
+ * poll_state_synchronize_srcu(), which will return true if a full grace
+ * period has elapsed in the meantime.  Unlike get_state_synchronize_srcu(),
+ * this function also ensures that any needed SRCU grace period will be
+ * started.  This convenience does come at a cost in terms of CPU overhead.
+ */
+unsigned long start_poll_synchronize_srcu(struct srcu_struct *ssp)
+{
+	return srcu_gp_start_if_needed(ssp, NULL, true);
+}
+EXPORT_SYMBOL_GPL(start_poll_synchronize_srcu);
+
+/**
+ * poll_state_synchronize_srcu - Has cookie's grace period ended?
+ * @ssp: srcu_struct to provide cookie for.
+ * @cookie: Return value from get_state_synchronize_srcu() or start_poll_synchronize_srcu().
+ *
+ * This function takes the cookie that was returned from either
+ * get_state_synchronize_srcu() or start_poll_synchronize_srcu(), and
+ * returns @true if an SRCU grace period elapsed since the time that the
+ * cookie was created.
+ *
+ * Because cookies are finite in size, wrapping/overflow is possible.
+ * This is more pronounced on 32-bit systems where cookies are 32 bits,
+ * where in theory wrapping could happen in about 14 hours assuming
+ * 25-microsecond expedited SRCU grace periods.  However, a more likely
+ * overflow lower bound is on the order of 24 days in the case of
+ * one-millisecond SRCU grace periods.  Of course, wrapping in a 64-bit
+ * system requires geologic timespans, as in more than seven million years
+ * even for expedited SRCU grace periods.
+ *
+ * Wrapping/overflow is much more of an issue for CONFIG_SMP=n systems
+ * that also have CONFIG_PREEMPTION=n, which selects Tiny SRCU.  This uses
+ * a 16-bit cookie, which rcutorture routinely wraps in a matter of a
+ * few minutes.  If this proves to be a problem, this counter will be
+ * expanded to the same size as for Tree SRCU.
+ */
+bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie)
+{
+	if (!rcu_seq_done(&ssp->srcu_gp_seq, cookie))
+		return false;
+	// Ensure that the end of the SRCU grace period happens before
+	// any subsequent code that the caller might execute.
+	smp_mb(); // ^^^
+	return true;
+}
+EXPORT_SYMBOL_GPL(poll_state_synchronize_srcu);
+
 /*
  * Callback function for srcu_barrier() use.
  */
@@ -1160,6 +1242,7 @@ static void srcu_advance_state(struct srcu_struct *ssp)
  */
 static void srcu_invoke_callbacks(struct work_struct *work)
 {
+	long len;
 	bool more;
 	struct rcu_cblist ready_cbs;
 	struct rcu_head *rhp;
@@ -1182,6 +1265,7 @@ static void srcu_invoke_callbacks(struct work_struct *work)
 	/* We are on the job!  Extract and invoke ready callbacks. */
 	sdp->srcu_cblist_invoking = true;
 	rcu_segcblist_extract_done_cbs(&sdp->srcu_cblist, &ready_cbs);
+	len = ready_cbs.len;
 	spin_unlock_irq_rcu_node(sdp);
 	rhp = rcu_cblist_dequeue(&ready_cbs);
 	for (; rhp != NULL; rhp = rcu_cblist_dequeue(&ready_cbs)) {
@@ -1190,13 +1274,14 @@ static void srcu_invoke_callbacks(struct work_struct *work)
 		rhp->func(rhp);
 		local_bh_enable();
 	}
+	WARN_ON_ONCE(ready_cbs.len);
 
 	/*
 	 * Update counts, accelerate new callbacks, and if needed,
 	 * schedule another round of callback invocation.
 	 */
 	spin_lock_irq_rcu_node(sdp);
-	rcu_segcblist_insert_count(&sdp->srcu_cblist, &ready_cbs);
+	rcu_segcblist_add_len(&sdp->srcu_cblist, -len);
 	(void)rcu_segcblist_accelerate(&sdp->srcu_cblist,
 				       rcu_seq_snap(&ssp->srcu_gp_seq));
 	sdp->srcu_cblist_invoking = false;

kernel/rcu/tasks.h

@@ -1224,6 +1224,82 @@ void show_rcu_tasks_gp_kthreads(void)
 }
 #endif /* #ifndef CONFIG_TINY_RCU */
 
+#ifdef CONFIG_PROVE_RCU
+struct rcu_tasks_test_desc {
+	struct rcu_head rh;
+	const char *name;
+	bool notrun;
+};
+
+static struct rcu_tasks_test_desc tests[] = {
+	{
+		.name = "call_rcu_tasks()",
+		/* If not defined, the test is skipped. */
+		.notrun = !IS_ENABLED(CONFIG_TASKS_RCU),
+	},
+	{
+		.name = "call_rcu_tasks_rude()",
+		/* If not defined, the test is skipped. */
+		.notrun = !IS_ENABLED(CONFIG_TASKS_RUDE_RCU),
+	},
+	{
+		.name = "call_rcu_tasks_trace()",
+		/* If not defined, the test is skipped. */
+		.notrun = !IS_ENABLED(CONFIG_TASKS_TRACE_RCU)
+	}
+};
+
+static void test_rcu_tasks_callback(struct rcu_head *rhp)
+{
+	struct rcu_tasks_test_desc *rttd =
+		container_of(rhp, struct rcu_tasks_test_desc, rh);
+
+	pr_info("Callback from %s invoked.\n", rttd->name);
+
+	rttd->notrun = true;
+}
+
+static void rcu_tasks_initiate_self_tests(void)
+{
+	pr_info("Running RCU-tasks wait API self tests\n");
+#ifdef CONFIG_TASKS_RCU
+	synchronize_rcu_tasks();
+	call_rcu_tasks(&tests[0].rh, test_rcu_tasks_callback);
+#endif
+
+#ifdef CONFIG_TASKS_RUDE_RCU
+	synchronize_rcu_tasks_rude();
+	call_rcu_tasks_rude(&tests[1].rh, test_rcu_tasks_callback);
+#endif
+
+#ifdef CONFIG_TASKS_TRACE_RCU
+	synchronize_rcu_tasks_trace();
+	call_rcu_tasks_trace(&tests[2].rh, test_rcu_tasks_callback);
+#endif
+}
+
+static int rcu_tasks_verify_self_tests(void)
+{
+	int ret = 0;
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(tests); i++) {
+		if (!tests[i].notrun) {		// still hanging.
+			pr_err("%s has been failed.\n", tests[i].name);
+			ret = -1;
+		}
+	}
+
+	if (ret)
+		WARN_ON(1);
+
+	return ret;
+}
+late_initcall(rcu_tasks_verify_self_tests);
+#else /* #ifdef CONFIG_PROVE_RCU */
+static void rcu_tasks_initiate_self_tests(void) { }
+#endif /* #else #ifdef CONFIG_PROVE_RCU */
+
 void __init rcu_init_tasks_generic(void)
 {
 #ifdef CONFIG_TASKS_RCU
@@ -1237,6 +1313,9 @@ void __init rcu_init_tasks_generic(void)
 #ifdef CONFIG_TASKS_TRACE_RCU
 	rcu_spawn_tasks_trace_kthread();
 #endif
+
+	// Run the self-tests.
+	rcu_tasks_initiate_self_tests();
 }
 
 #else /* #ifdef CONFIG_TASKS_RCU_GENERIC */

kernel/rcu/tree.h

@@ -201,6 +201,7 @@ struct rcu_data {
 	/* 5) Callback offloading. */
 #ifdef CONFIG_RCU_NOCB_CPU
 	struct swait_queue_head nocb_cb_wq; /* For nocb kthreads to sleep on. */
+	struct swait_queue_head nocb_state_wq; /* For offloading state changes */
 	struct task_struct *nocb_gp_kthread;
 	raw_spinlock_t nocb_lock;	/* Guard following pair of fields. */
 	atomic_t nocb_lock_contended;	/* Contention experienced. */
@@ -256,6 +257,7 @@ struct rcu_data {
 };
 
 /* Values for nocb_defer_wakeup field in struct rcu_data. */
+#define RCU_NOCB_WAKE_OFF	-1
 #define RCU_NOCB_WAKE_NOT	0
 #define RCU_NOCB_WAKE		1
 #define RCU_NOCB_WAKE_FORCE	2

kernel/rcu/tree_exp.h

@@ -545,7 +545,7 @@ static void synchronize_rcu_expedited_wait(void)
 			data_race(rnp_root->expmask),
 			".T"[!!data_race(rnp_root->exp_tasks)]);
 		if (ndetected) {
-			pr_err("blocking rcu_node structures:");
+			pr_err("blocking rcu_node structures (internal RCU debug):");
 			rcu_for_each_node_breadth_first(rnp) {
 				if (rnp == rnp_root)
 					continue; /* printed unconditionally */

kernel/rcu/tree_stall.h

@@ -266,6 +266,7 @@ static int rcu_print_task_stall(struct rcu_node *rnp, unsigned long flags)
 	struct task_struct *t;
 	struct task_struct *ts[8];
 
+	lockdep_assert_irqs_disabled();
 	if (!rcu_preempt_blocked_readers_cgp(rnp))
 		return 0;
 	pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
@@ -290,6 +291,7 @@ static int rcu_print_task_stall(struct rcu_node *rnp, unsigned long flags)
 				".q"[rscr.rs.b.need_qs],
 				".e"[rscr.rs.b.exp_hint],
 				".l"[rscr.on_blkd_list]);
+		lockdep_assert_irqs_disabled();
 		put_task_struct(t);
 		ndetected++;
 	}
@@ -333,9 +335,12 @@ static void rcu_dump_cpu_stacks(void)
 	rcu_for_each_leaf_node(rnp) {
 		raw_spin_lock_irqsave_rcu_node(rnp, flags);
 		for_each_leaf_node_possible_cpu(rnp, cpu)
-			if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu))
-				if (!trigger_single_cpu_backtrace(cpu))
+			if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu)) {
+				if (cpu_is_offline(cpu))
+					pr_err("Offline CPU %d blocking current GP.\n", cpu);
+				else if (!trigger_single_cpu_backtrace(cpu))
 					dump_cpu_task(cpu);
+			}
 		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 	}
 }
@@ -449,25 +454,66 @@ static void print_cpu_stall_info(int cpu)
 /* Complain about starvation of grace-period kthread.  */
 static void rcu_check_gp_kthread_starvation(void)
 {
+	int cpu;
 	struct task_struct *gpk = rcu_state.gp_kthread;
 	unsigned long j;
 
 	if (rcu_is_gp_kthread_starving(&j)) {
+		cpu = gpk ? task_cpu(gpk) : -1;
 		pr_err("%s kthread starved for %ld jiffies! g%ld f%#x %s(%d) ->state=%#lx ->cpu=%d\n",
 		       rcu_state.name, j,
 		       (long)rcu_seq_current(&rcu_state.gp_seq),
 		       data_race(rcu_state.gp_flags),
 		       gp_state_getname(rcu_state.gp_state), rcu_state.gp_state,
-		       gpk ? gpk->state : ~0, gpk ? task_cpu(gpk) : -1);
+		       gpk ? gpk->state : ~0, cpu);
 		if (gpk) {
 			pr_err("\tUnless %s kthread gets sufficient CPU time, OOM is now expected behavior.\n", rcu_state.name);
 			pr_err("RCU grace-period kthread stack dump:\n");
 			sched_show_task(gpk);
+			if (cpu >= 0) {
+				if (cpu_is_offline(cpu)) {
+					pr_err("RCU GP kthread last ran on offline CPU %d.\n", cpu);
+				} else  {
+					pr_err("Stack dump where RCU GP kthread last ran:\n");
+					if (!trigger_single_cpu_backtrace(cpu))
+						dump_cpu_task(cpu);
+				}
+			}
 			wake_up_process(gpk);
 		}
 	}
 }
 
+/* Complain about missing wakeups from expired fqs wait timer */
+static void rcu_check_gp_kthread_expired_fqs_timer(void)
+{
+	struct task_struct *gpk = rcu_state.gp_kthread;
+	short gp_state;
+	unsigned long jiffies_fqs;
+	int cpu;
+
+	/*
+	 * Order reads of .gp_state and .jiffies_force_qs.
+	 * Matching smp_wmb() is present in rcu_gp_fqs_loop().
+	 */
+	gp_state = smp_load_acquire(&rcu_state.gp_state);
+	jiffies_fqs = READ_ONCE(rcu_state.jiffies_force_qs);
+
+	if (gp_state == RCU_GP_WAIT_FQS &&
+	    time_after(jiffies, jiffies_fqs + RCU_STALL_MIGHT_MIN) &&
+	    gpk && !READ_ONCE(gpk->on_rq)) {
+		cpu = task_cpu(gpk);
+		pr_err("%s kthread timer wakeup didn't happen for %ld jiffies! g%ld f%#x %s(%d) ->state=%#lx\n",
+		       rcu_state.name, (jiffies - jiffies_fqs),
+		       (long)rcu_seq_current(&rcu_state.gp_seq),
+		       data_race(rcu_state.gp_flags),
+		       gp_state_getname(RCU_GP_WAIT_FQS), RCU_GP_WAIT_FQS,
+		       gpk->state);
+		pr_err("\tPossible timer handling issue on cpu=%d timer-softirq=%u\n",
+		       cpu, kstat_softirqs_cpu(TIMER_SOFTIRQ, cpu));
+	}
+}
+
 static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps)
 {
 	int cpu;
@@ -478,6 +524,8 @@ static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps)
 	struct rcu_node *rnp;
 	long totqlen = 0;
 
+	lockdep_assert_irqs_disabled();
+
 	/* Kick and suppress, if so configured. */
 	rcu_stall_kick_kthreads();
 	if (rcu_stall_is_suppressed())
@@ -499,6 +547,7 @@ static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps)
 				}
 		}
 		ndetected += rcu_print_task_stall(rnp, flags); // Releases rnp->lock.
+		lockdep_assert_irqs_disabled();
 	}
 
 	for_each_possible_cpu(cpu)
@@ -529,6 +578,7 @@ static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps)
 		WRITE_ONCE(rcu_state.jiffies_stall,
 			   jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
 
+	rcu_check_gp_kthread_expired_fqs_timer();
 	rcu_check_gp_kthread_starvation();
 
 	panic_on_rcu_stall();
@@ -544,6 +594,8 @@ static void print_cpu_stall(unsigned long gps)
 	struct rcu_node *rnp = rcu_get_root();
 	long totqlen = 0;
 
+	lockdep_assert_irqs_disabled();
+
 	/* Kick and suppress, if so configured. */
 	rcu_stall_kick_kthreads();
 	if (rcu_stall_is_suppressed())
@@ -564,6 +616,7 @@ static void print_cpu_stall(unsigned long gps)
 		jiffies - gps,
 		(long)rcu_seq_current(&rcu_state.gp_seq), totqlen);
 
+	rcu_check_gp_kthread_expired_fqs_timer();
 	rcu_check_gp_kthread_starvation();
 
 	rcu_dump_cpu_stacks();
@@ -598,6 +651,7 @@ static void check_cpu_stall(struct rcu_data *rdp)
 	unsigned long js;
 	struct rcu_node *rnp;
 
+	lockdep_assert_irqs_disabled();
 	if ((rcu_stall_is_suppressed() && !READ_ONCE(rcu_kick_kthreads)) ||
 	    !rcu_gp_in_progress())
 		return;

kernel/rcu/update.c

@@ -56,8 +56,10 @@
 #ifndef CONFIG_TINY_RCU
 module_param(rcu_expedited, int, 0);
 module_param(rcu_normal, int, 0);
-static int rcu_normal_after_boot;
+static int rcu_normal_after_boot = IS_ENABLED(CONFIG_PREEMPT_RT);
+#ifndef CONFIG_PREEMPT_RT
 module_param(rcu_normal_after_boot, int, 0);
+#endif
 #endif /* #ifndef CONFIG_TINY_RCU */
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC

kernel/scftorture.c

@@ -398,6 +398,7 @@ static void scftorture_invoke_one(struct scf_statistics *scfp, struct torture_ra
 static int scftorture_invoker(void *arg)
 {
 	int cpu;
+	int curcpu;
 	DEFINE_TORTURE_RANDOM(rand);
 	struct scf_statistics *scfp = (struct scf_statistics *)arg;
 	bool was_offline = false;
@@ -412,7 +413,10 @@ static int scftorture_invoker(void *arg)
 	VERBOSE_SCFTORTOUT("scftorture_invoker %d: Waiting for all SCF torturers from cpu %d", scfp->cpu, smp_processor_id());
 
 	// Make sure that the CPU is affinitized appropriately during testing.
-	WARN_ON_ONCE(smp_processor_id() != scfp->cpu);
+	curcpu = smp_processor_id();
+	WARN_ONCE(curcpu != scfp->cpu % nr_cpu_ids,
+		  "%s: Wanted CPU %d, running on %d, nr_cpu_ids = %d\n",
+		  __func__, scfp->cpu, curcpu, nr_cpu_ids);
 
 	if (!atomic_dec_return(&n_started))
 		while (atomic_read_acquire(&n_started)) {

kernel/sched/core.c

@@ -3478,7 +3478,7 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
 
 /**
  * try_invoke_on_locked_down_task - Invoke a function on task in fixed state
- * @p: Process for which the function is to be invoked.
+ * @p: Process for which the function is to be invoked, can be @current.
  * @func: Function to invoke.
  * @arg: Argument to function.
  *
@@ -3496,12 +3496,11 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
  */
 bool try_invoke_on_locked_down_task(struct task_struct *p, bool (*func)(struct task_struct *t, void *arg), void *arg)
 {
-	bool ret = false;
 	struct rq_flags rf;
+	bool ret = false;
 	struct rq *rq;
 
-	lockdep_assert_irqs_enabled();
-	raw_spin_lock_irq(&p->pi_lock);
+	raw_spin_lock_irqsave(&p->pi_lock, rf.flags);
 	if (p->on_rq) {
 		rq = __task_rq_lock(p, &rf);
 		if (task_rq(p) == rq)
@@ -3518,7 +3517,7 @@ bool try_invoke_on_locked_down_task(struct task_struct *p, bool (*func)(struct t
 				ret = func(p, arg);
 		}
 	}
-	raw_spin_unlock_irq(&p->pi_lock);
+	raw_spin_unlock_irqrestore(&p->pi_lock, rf.flags);
 	return ret;
 }
 

kernel/time/timer.c

@@ -1237,6 +1237,20 @@ int try_to_del_timer_sync(struct timer_list *timer)
 }
 EXPORT_SYMBOL(try_to_del_timer_sync);
 
+bool timer_curr_running(struct timer_list *timer)
+{
+	int i;
+
+	for (i = 0; i < NR_BASES; i++) {
+		struct timer_base *base = this_cpu_ptr(&timer_bases[i]);
+
+		if (base->running_timer == timer)
+			return true;
+	}
+
+	return false;
+}
+
 #ifdef CONFIG_PREEMPT_RT
 static __init void timer_base_init_expiry_lock(struct timer_base *base)
 {

lib/percpu-refcount.c

@@ -5,6 +5,7 @@
 #include <linux/sched.h>
 #include <linux/wait.h>
 #include <linux/slab.h>
+#include <linux/mm.h>
 #include <linux/percpu-refcount.h>
 
 /*
@@ -168,6 +169,7 @@ static void percpu_ref_switch_to_atomic_rcu(struct rcu_head *rcu)
 			struct percpu_ref_data, rcu);
 	struct percpu_ref *ref = data->ref;
 	unsigned long __percpu *percpu_count = percpu_count_ptr(ref);
+	static atomic_t underflows;
 	unsigned long count = 0;
 	int cpu;
 
@@ -191,9 +193,13 @@ static void percpu_ref_switch_to_atomic_rcu(struct rcu_head *rcu)
 	 */
 	atomic_long_add((long)count - PERCPU_COUNT_BIAS, &data->count);
 
-	WARN_ONCE(atomic_long_read(&data->count) <= 0,
+	if (WARN_ONCE(atomic_long_read(&data->count) <= 0,
 		      "percpu ref (%ps) <= 0 (%ld) after switching to atomic",
-		  data->release, atomic_long_read(&data->count));
+		      data->release, atomic_long_read(&data->count)) &&
+	    atomic_inc_return(&underflows) < 4) {
+		pr_err("%s(): percpu_ref underflow", __func__);
+		mem_dump_obj(data);
+	}
 
 	/* @ref is viewed as dead on all CPUs, send out switch confirmation */
 	percpu_ref_call_confirm_rcu(rcu);

mm/slab.h

@@ -615,4 +615,16 @@ static inline bool slab_want_init_on_free(struct kmem_cache *c)
 	return false;
 }
 
+#define KS_ADDRS_COUNT 16
+struct kmem_obj_info {
+	void *kp_ptr;
+	struct page *kp_page;
+	void *kp_objp;
+	unsigned long kp_data_offset;
+	struct kmem_cache *kp_slab_cache;
+	void *kp_ret;
+	void *kp_stack[KS_ADDRS_COUNT];
+};
+void kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct page *page);
+
 #endif /* MM_SLAB_H */

tools/testing/selftests/rcutorture/bin/console-badness.sh

@@ -14,4 +14,5 @@ egrep 'Badness|WARNING:|Warn|BUG|===========|Call Trace:|Oops:|detected stalls o
 grep -v 'ODEBUG: ' |
 grep -v 'This means that this is a DEBUG kernel and it is' |
 grep -v 'Warning: unable to open an initial console' |
+grep -v 'Warning: Failed to add ttynull console. No stdin, stdout, and stderr.*the init process!' |
 grep -v 'NOHZ tick-stop error: Non-RCU local softirq work is pending, handler'