Commit aea4869f authored by Linus Torvalds's avatar Linus Torvalds

Merge branch 'core-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull core fixes from Ingo Molnar:
 "The tree contains two RCU fixes and a compiler quirk comment fix"

* 'core-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  rcu: Make rcu_barrier() understand about missing rcuo kthreads
  compiler/gcc4+: Remove inaccurate comment about 'asm goto' miscompiles
  rcu: More on deadlock between CPU hotplug and expedited grace periods
parents 0f4b0676 21ee24bf
......@@ -71,7 +71,6 @@
* http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58670
*
* Work it around via a compiler barrier quirk suggested by Jakub Jelinek.
* Fixed in GCC 4.8.2 and later versions.
*
* (asm goto is automatically volatile - the naming reflects this.)
*/
......
......@@ -53,7 +53,6 @@
* http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58670
*
* Work it around via a compiler barrier quirk suggested by Jakub Jelinek.
* Fixed in GCC 4.8.2 and later versions.
*
* (asm goto is automatically volatile - the naming reflects this.)
*/
......
......@@ -660,18 +660,18 @@ TRACE_EVENT(rcu_torture_read,
/*
* Tracepoint for _rcu_barrier() execution. The string "s" describes
* the _rcu_barrier phase:
* "Begin": rcu_barrier_callback() started.
* "Check": rcu_barrier_callback() checking for piggybacking.
* "EarlyExit": rcu_barrier_callback() piggybacked, thus early exit.
* "Inc1": rcu_barrier_callback() piggyback check counter incremented.
* "Offline": rcu_barrier_callback() found offline CPU
* "OnlineNoCB": rcu_barrier_callback() found online no-CBs CPU.
* "OnlineQ": rcu_barrier_callback() found online CPU with callbacks.
* "OnlineNQ": rcu_barrier_callback() found online CPU, no callbacks.
* "Begin": _rcu_barrier() started.
* "Check": _rcu_barrier() checking for piggybacking.
* "EarlyExit": _rcu_barrier() piggybacked, thus early exit.
* "Inc1": _rcu_barrier() piggyback check counter incremented.
* "OfflineNoCB": _rcu_barrier() found callback on never-online CPU
* "OnlineNoCB": _rcu_barrier() found online no-CBs CPU.
* "OnlineQ": _rcu_barrier() found online CPU with callbacks.
* "OnlineNQ": _rcu_barrier() found online CPU, no callbacks.
* "IRQ": An rcu_barrier_callback() callback posted on remote CPU.
* "CB": An rcu_barrier_callback() invoked a callback, not the last.
* "LastCB": An rcu_barrier_callback() invoked the last callback.
* "Inc2": rcu_barrier_callback() piggyback check counter incremented.
* "Inc2": _rcu_barrier() piggyback check counter incremented.
* The "cpu" argument is the CPU or -1 if meaningless, the "cnt" argument
* is the count of remaining callbacks, and "done" is the piggybacking count.
*/
......
......@@ -64,6 +64,8 @@ static struct {
* an ongoing cpu hotplug operation.
*/
int refcount;
/* And allows lockless put_online_cpus(). */
atomic_t puts_pending;
#ifdef CONFIG_DEBUG_LOCK_ALLOC
struct lockdep_map dep_map;
......@@ -113,7 +115,11 @@ void put_online_cpus(void)
{
if (cpu_hotplug.active_writer == current)
return;
mutex_lock(&cpu_hotplug.lock);
if (!mutex_trylock(&cpu_hotplug.lock)) {
atomic_inc(&cpu_hotplug.puts_pending);
cpuhp_lock_release();
return;
}
if (WARN_ON(!cpu_hotplug.refcount))
cpu_hotplug.refcount++; /* try to fix things up */
......@@ -155,6 +161,12 @@ void cpu_hotplug_begin(void)
cpuhp_lock_acquire();
for (;;) {
mutex_lock(&cpu_hotplug.lock);
if (atomic_read(&cpu_hotplug.puts_pending)) {
int delta;
delta = atomic_xchg(&cpu_hotplug.puts_pending, 0);
cpu_hotplug.refcount -= delta;
}
if (likely(!cpu_hotplug.refcount))
break;
__set_current_state(TASK_UNINTERRUPTIBLE);
......
......@@ -3299,11 +3299,16 @@ static void _rcu_barrier(struct rcu_state *rsp)
continue;
rdp = per_cpu_ptr(rsp->rda, cpu);
if (rcu_is_nocb_cpu(cpu)) {
if (!rcu_nocb_cpu_needs_barrier(rsp, cpu)) {
_rcu_barrier_trace(rsp, "OfflineNoCB", cpu,
rsp->n_barrier_done);
} else {
_rcu_barrier_trace(rsp, "OnlineNoCB", cpu,
rsp->n_barrier_done);
atomic_inc(&rsp->barrier_cpu_count);
__call_rcu(&rdp->barrier_head, rcu_barrier_callback,
rsp, cpu, 0);
__call_rcu(&rdp->barrier_head,
rcu_barrier_callback, rsp, cpu, 0);
}
} else if (ACCESS_ONCE(rdp->qlen)) {
_rcu_barrier_trace(rsp, "OnlineQ", cpu,
rsp->n_barrier_done);
......
......@@ -587,6 +587,7 @@ static void print_cpu_stall_info(struct rcu_state *rsp, int cpu);
static void print_cpu_stall_info_end(void);
static void zero_cpu_stall_ticks(struct rcu_data *rdp);
static void increment_cpu_stall_ticks(void);
static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu);
static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq);
static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp);
static void rcu_init_one_nocb(struct rcu_node *rnp);
......
......@@ -2049,6 +2049,33 @@ static void wake_nocb_leader(struct rcu_data *rdp, bool force)
}
}
/*
* Does the specified CPU need an RCU callback for the specified flavor
* of rcu_barrier()?
*/
static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu)
{
struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
struct rcu_head *rhp;
/* No-CBs CPUs might have callbacks on any of three lists. */
rhp = ACCESS_ONCE(rdp->nocb_head);
if (!rhp)
rhp = ACCESS_ONCE(rdp->nocb_gp_head);
if (!rhp)
rhp = ACCESS_ONCE(rdp->nocb_follower_head);
/* Having no rcuo kthread but CBs after scheduler starts is bad! */
if (!ACCESS_ONCE(rdp->nocb_kthread) && rhp) {
/* RCU callback enqueued before CPU first came online??? */
pr_err("RCU: Never-onlined no-CBs CPU %d has CB %p\n",
cpu, rhp->func);
WARN_ON_ONCE(1);
}
return !!rhp;
}
/*
* Enqueue the specified string of rcu_head structures onto the specified
* CPU's no-CBs lists. The CPU is specified by rdp, the head of the
......@@ -2642,6 +2669,12 @@ static bool init_nocb_callback_list(struct rcu_data *rdp)
#else /* #ifdef CONFIG_RCU_NOCB_CPU */
static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu)
{
WARN_ON_ONCE(1); /* Should be dead code. */
return false;
}
static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
{
}
......
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