padata: update documentation

Remove references to unused functions, standardize language, update to
reflect new functionality, migrate to rst format, and fix all kernel-doc
warnings.

Fixes: 815613da ("kernel/padata.c: removed unused code")
Signed-off-by: Daniel Jordan <daniel.m.jordan@oracle.com>
Cc: Eric Biggers <ebiggers@kernel.org>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Steffen Klassert <steffen.klassert@secunet.com>
Cc: linux-crypto@vger.kernel.org
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Daniel Jordan <daniel.m.jordan@oracle.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Documentation/core-api/index.rst

@@ -39,6 +39,7 @@ Core utilities
    ../RCU/index
    gcc-plugins
    symbol-namespaces
+   padata
 
 
 Interfaces for kernel debugging

Documentation/padata.txt → Documentation/core-api/padata.rst

+.. SPDX-License-Identifier: GPL-2.0
+
 =======================================
 The padata parallel execution mechanism
 =======================================
 
-:Last updated: for 2.6.36
+:Date: December 2019
+
+Padata is a mechanism by which the kernel can farm jobs out to be done in
+parallel on multiple CPUs while retaining their ordering.  It was developed for
+use with the IPsec code, which needs to be able to perform encryption and
+decryption on large numbers of packets without reordering those packets.  The
+crypto developers made a point of writing padata in a sufficiently general
+fashion that it could be put to other uses as well.
+
+Usage
+=====
 
-Padata is a mechanism by which the kernel can farm work out to be done in
-parallel on multiple CPUs while retaining the ordering of tasks.  It was
-developed for use with the IPsec code, which needs to be able to perform
-encryption and decryption on large numbers of packets without reordering
-those packets.  The crypto developers made a point of writing padata in a
-sufficiently general fashion that it could be put to other uses as well.
+Initializing
+------------
 
 The first step in using padata is to set up a padata_instance structure for
-overall control of how tasks are to be run::
+overall control of how jobs are to be run::
 
     #include <linux/padata.h>
 
-    struct padata_instance *padata_alloc(const char *name,
-					 const struct cpumask *pcpumask,
-					 const struct cpumask *cbcpumask);
+    struct padata_instance *padata_alloc_possible(const char *name);
 
 'name' simply identifies the instance.
 
-The pcpumask describes which processors will be used to execute work
-submitted to this instance in parallel. The cbcpumask defines which
-processors are allowed to be used as the serialization callback processor.
-The workqueue wq is where the work will actually be done; it should be
-a multithreaded queue, naturally.
+There are functions for enabling and disabling the instance::
 
-To allocate a padata instance with the cpu_possible_mask for both
-cpumasks this helper function can be used::
+    int padata_start(struct padata_instance *pinst);
+    void padata_stop(struct padata_instance *pinst);
 
-    struct padata_instance *padata_alloc_possible(struct workqueue_struct *wq);
+These functions are setting or clearing the "PADATA_INIT" flag; if that flag is
+not set, other functions will refuse to work.  padata_start() returns zero on
+success (flag set) or -EINVAL if the padata cpumask contains no active CPU
+(flag not set).  padata_stop() clears the flag and blocks until the padata
+instance is unused.
 
-Note: Padata maintains two kinds of cpumasks internally. The user supplied
-cpumasks, submitted by padata_alloc/padata_alloc_possible and the 'usable'
-cpumasks. The usable cpumasks are always a subset of active CPUs in the
-user supplied cpumasks; these are the cpumasks padata actually uses. So
-it is legal to supply a cpumask to padata that contains offline CPUs.
-Once an offline CPU in the user supplied cpumask comes online, padata
-is going to use it.
+Finally, complete padata initialization by allocating a padata_shell::
 
-There are functions for enabling and disabling the instance::
+   struct padata_shell *padata_alloc_shell(struct padata_instance *pinst);
 
-    int padata_start(struct padata_instance *pinst);
-    void padata_stop(struct padata_instance *pinst);
+A padata_shell is used to submit a job to padata and allows a series of such
+jobs to be serialized independently.  A padata_instance may have one or more
+padata_shells associated with it, each allowing a separate series of jobs.
 
-These functions are setting or clearing the "PADATA_INIT" flag;
-if that flag is not set, other functions will refuse to work.
-padata_start returns zero on success (flag set) or -EINVAL if the
-padata cpumask contains no active CPU (flag not set).
-padata_stop clears the flag and blocks until the padata instance
-is unused.
+Modifying cpumasks
+------------------
 
-The list of CPUs to be used can be adjusted with these functions::
+The CPUs used to run jobs can be changed in two ways, programatically with
+padata_set_cpumask() or via sysfs.  The former is defined::
 
-    int padata_set_cpumasks(struct padata_instance *pinst,
-			    cpumask_var_t pcpumask,
-			    cpumask_var_t cbcpumask);
     int padata_set_cpumask(struct padata_instance *pinst, int cpumask_type,
 			   cpumask_var_t cpumask);
-    int padata_add_cpu(struct padata_instance *pinst, int cpu, int mask);
-    int padata_remove_cpu(struct padata_instance *pinst, int cpu, int mask);
 
-Changing the CPU masks are expensive operations, though, so it should not be
-done with great frequency.
+Here cpumask_type is one of PADATA_CPU_PARALLEL or PADATA_CPU_SERIAL, where a
+parallel cpumask describes which processors will be used to execute jobs
+submitted to this instance in parallel and a serial cpumask defines which
+processors are allowed to be used as the serialization callback processor.
+cpumask specifies the new cpumask to use.
+
+There may be sysfs files for an instance's cpumasks.  For example, pcrypt's
+live in /sys/kernel/pcrypt/<instance-name>.  Within an instance's directory
+there are two files, parallel_cpumask and serial_cpumask, and either cpumask
+may be changed by echoing a bitmask into the file, for example::
+
+    echo f > /sys/kernel/pcrypt/pencrypt/parallel_cpumask
+
+Reading one of these files shows the user-supplied cpumask, which may be
+different from the 'usable' cpumask.
 
-It's possible to change both cpumasks of a padata instance with
-padata_set_cpumasks by specifying the cpumasks for parallel execution (pcpumask)
-and for the serial callback function (cbcpumask). padata_set_cpumask is used to
-change just one of the cpumasks. Here cpumask_type is one of PADATA_CPU_SERIAL,
-PADATA_CPU_PARALLEL and cpumask specifies the new cpumask to use.
-To simply add or remove one CPU from a certain cpumask the functions
-padata_add_cpu/padata_remove_cpu are used. cpu specifies the CPU to add or
-remove and mask is one of PADATA_CPU_SERIAL, PADATA_CPU_PARALLEL.
+Padata maintains two pairs of cpumasks internally, the user-supplied cpumasks
+and the 'usable' cpumasks.  (Each pair consists of a parallel and a serial
+cpumask.)  The user-supplied cpumasks default to all possible CPUs on instance
+allocation and may be changed as above.  The usable cpumasks are always a
+subset of the user-supplied cpumasks and contain only the online CPUs in the
+user-supplied masks; these are the cpumasks padata actually uses.  So it is
+legal to supply a cpumask to padata that contains offline CPUs.  Once an
+offline CPU in the user-supplied cpumask comes online, padata is going to use
+it.
+
+Changing the CPU masks are expensive operations, so it should not be done with
+great frequency.
+
+Running A Job
+-------------
 
 Actually submitting work to the padata instance requires the creation of a
-padata_priv structure::
+padata_priv structure, which represents one job::
 
     struct padata_priv {
         /* Other stuff here... */
@@ -91,34 +104,40 @@ parallel() and serial() functions should be provided.  Those functions will
 be called in the process of getting the work done as we will see
 momentarily.
 
-The submission of work is done with::
+The submission of the job is done with::
 
-    int padata_do_parallel(struct padata_instance *pinst,
-		           struct padata_priv *padata, int cb_cpu);
+    int padata_do_parallel(struct padata_shell *ps,
+		           struct padata_priv *padata, int *cb_cpu);
 
-The pinst and padata structures must be set up as described above; cb_cpu
-specifies which CPU will be used for the final callback when the work is
-done; it must be in the current instance's CPU mask.  The return value from
-padata_do_parallel() is zero on success, indicating that the work is in
+The ps and padata structures must be set up as described above; cb_cpu
+points to the preferred CPU to be used for the final callback when the job is
+done; it must be in the current instance's CPU mask (if not the cb_cpu pointer
+is updated to point to the CPU actually chosen).  The return value from
+padata_do_parallel() is zero on success, indicating that the job is in
 progress. -EBUSY means that somebody, somewhere else is messing with the
-instance's CPU mask, while -EINVAL is a complaint about cb_cpu not being
-in that CPU mask or about a not running instance.
+instance's CPU mask, while -EINVAL is a complaint about cb_cpu not being in the
+serial cpumask, no online CPUs in the parallel or serial cpumasks, or a stopped
+instance.
 
-Each task submitted to padata_do_parallel() will, in turn, be passed to
+Each job submitted to padata_do_parallel() will, in turn, be passed to
 exactly one call to the above-mentioned parallel() function, on one CPU, so
-true parallelism is achieved by submitting multiple tasks.  parallel() runs with
+true parallelism is achieved by submitting multiple jobs.  parallel() runs with
 software interrupts disabled and thus cannot sleep.  The parallel()
 function gets the padata_priv structure pointer as its lone parameter;
 information about the actual work to be done is probably obtained by using
 container_of() to find the enclosing structure.
 
 Note that parallel() has no return value; the padata subsystem assumes that
-parallel() will take responsibility for the task from this point.  The work
+parallel() will take responsibility for the job from this point.  The job
 need not be completed during this call, but, if parallel() leaves work
 outstanding, it should be prepared to be called again with a new job before
-the previous one completes.  When a task does complete, parallel() (or
-whatever function actually finishes the job) should inform padata of the
-fact with a call to::
+the previous one completes.
+
+Serializing Jobs
+----------------
+
+When a job does complete, parallel() (or whatever function actually finishes
+the work) should inform padata of the fact with a call to::
 
     void padata_do_serial(struct padata_priv *padata);
 
@@ -127,13 +146,24 @@ serial() function in the padata_priv structure.  That call will happen on
 the CPU requested in the initial call to padata_do_parallel(); it, too, is
 run with local software interrupts disabled.
 Note that this call may be deferred for a while since the padata code takes
-pains to ensure that tasks are completed in the order in which they were
+pains to ensure that jobs are completed in the order in which they were
 submitted.
 
-The one remaining function in the padata API should be called to clean up
-when a padata instance is no longer needed::
+Destroying
+----------
+
+Cleaning up a padata instance predictably involves calling the three free
+functions that correspond to the allocation in reverse::
 
+    void padata_free_shell(struct padata_shell *ps);
+    void padata_stop(struct padata_instance *pinst);
     void padata_free(struct padata_instance *pinst);
 
-This function will busy-wait while any remaining tasks are completed, so it
-might be best not to call it while there is work outstanding.
+It is the user's responsibility to ensure all outstanding jobs are complete
+before any of the above are called.
+
+Interface
+=========
+
+.. kernel-doc:: include/linux/padata.h
+.. kernel-doc:: kernel/padata.c

include/linux/padata.h

@@ -19,7 +19,7 @@
 #define PADATA_CPU_PARALLEL 0x02
 
 /**
- * struct padata_priv -  Embedded to the users data structure.
+ * struct padata_priv - Represents one job
  *
  * @list: List entry, to attach to the padata lists.
  * @pd: Pointer to the internal control structure.
@@ -42,7 +42,7 @@ struct padata_priv {
 };
 
 /**
- * struct padata_list
+ * struct padata_list - one per work type per CPU
  *
  * @list: List head.
  * @lock: List lock.
@@ -70,9 +70,6 @@ struct padata_serial_queue {
  *
  * @parallel: List to wait for parallelization.
  * @reorder: List to wait for reordering after parallel processing.
- * @serial: List to wait for serialization after reordering.
- * @pwork: work struct for parallelization.
- * @swork: work struct for serialization.
  * @work: work struct for parallelization.
  * @num_obj: Number of objects that are processed by this cpu.
  */
@@ -98,11 +95,11 @@ struct padata_cpumask {
  * struct parallel_data - Internal control structure, covers everything
  * that depends on the cpumask in use.
  *
- * @sh: padata_shell object.
+ * @ps: padata_shell object.
  * @pqueue: percpu padata queues used for parallelization.
  * @squeue: percpu padata queues used for serialuzation.
  * @refcnt: Number of objects holding a reference on this parallel_data.
- * @max_seq_nr:  Maximal used sequence number.
+ * @seq_nr: Sequence number of the parallelized data object.
  * @processed: Number of already processed objects.
  * @cpu: Next CPU to be processed.
  * @cpumask: The cpumasks in use for parallel and serial workers.
@@ -119,7 +116,7 @@ struct parallel_data {
 	int				cpu;
 	struct padata_cpumask		cpumask;
 	struct work_struct		reorder_work;
-	spinlock_t                      lock ____cacheline_aligned;
+	spinlock_t                      ____cacheline_aligned lock;
 };
 
 /**
@@ -142,7 +139,7 @@ struct padata_shell {
 /**
  * struct padata_instance - The overall control structure.
  *
- * @cpu_notifier: cpu hotplug notifier.
+ * @node: Used by CPU hotplug.
  * @parallel_wq: The workqueue used for parallel work.
  * @serial_wq: The workqueue used for serial work.
  * @pslist: List of padata_shell objects attached to this instance.

kernel/padata.c

@@ -2,7 +2,7 @@
 /*
  * padata.c - generic interface to process data streams in parallel
  *
- * See Documentation/padata.txt for an api documentation.
+ * See Documentation/core-api/padata.rst for more information.
  *
  * Copyright (C) 2008, 2009 secunet Security Networks AG
  * Copyright (C) 2008, 2009 Steffen Klassert <steffen.klassert@secunet.com>
@@ -99,6 +99,8 @@ static void padata_parallel_worker(struct work_struct *parallel_work)
  * The parallelization callback function will run with BHs off.
  * Note: Every object which is parallelized by padata_do_parallel
  * must be seen by padata_do_serial.
+ *
+ * Return: 0 on success or else negative error code.
  */
 int padata_do_parallel(struct padata_shell *ps,
 		       struct padata_priv *padata, int *cb_cpu)
@@ -163,12 +165,10 @@ EXPORT_SYMBOL(padata_do_parallel);
 /*
  * padata_find_next - Find the next object that needs serialization.
  *
- * Return values are:
- *
- * A pointer to the control struct of the next object that needs
+ * Return:
+ * * A pointer to the control struct of the next object that needs
  *   serialization, if present in one of the percpu reorder queues.
- *
- * NULL, if the next object that needs serialization will
+ * * NULL, if the next object that needs serialization will
  *   be parallel processed by another cpu and is not yet present in
  *   the cpu's reorder queue.
  */
@@ -582,13 +582,14 @@ static int __padata_set_cpumasks(struct padata_instance *pinst,
 }
 
 /**
- * padata_set_cpumask: Sets specified by @cpumask_type cpumask to the value
+ * padata_set_cpumask - Sets specified by @cpumask_type cpumask to the value
  *                      equivalent to @cpumask.
- *
  * @pinst: padata instance
  * @cpumask_type: PADATA_CPU_SERIAL or PADATA_CPU_PARALLEL corresponding
  *                to parallel and serial cpumasks respectively.
  * @cpumask: the cpumask to use
+ *
+ * Return: 0 on success or negative error code
  */
 int padata_set_cpumask(struct padata_instance *pinst, int cpumask_type,
 		       cpumask_var_t cpumask)
@@ -626,6 +627,8 @@ EXPORT_SYMBOL(padata_set_cpumask);
  * padata_start - start the parallel processing
  *
  * @pinst: padata instance to start
+ *
+ * Return: 0 on success or negative error code
  */
 int padata_start(struct padata_instance *pinst)
 {
@@ -880,6 +883,8 @@ static struct kobj_type padata_attr_type = {
  * @name: used to identify the instance
  * @pcpumask: cpumask that will be used for padata parallelization
  * @cbcpumask: cpumask that will be used for padata serialization
+ *
+ * Return: new instance on success, NULL on error
  */
 static struct padata_instance *padata_alloc(const char *name,
 					    const struct cpumask *pcpumask,
@@ -967,6 +972,8 @@ static struct padata_instance *padata_alloc(const char *name,
  *                         parallel workers.
  *
  * @name: used to identify the instance
+ *
+ * Return: new instance on success, NULL on error
  */
 struct padata_instance *padata_alloc_possible(const char *name)
 {
@@ -977,7 +984,7 @@ EXPORT_SYMBOL(padata_alloc_possible);
 /**
  * padata_free - free a padata instance
  *
- * @padata_inst: padata instance to free
+ * @pinst: padata instance to free
  */
 void padata_free(struct padata_instance *pinst)
 {
@@ -989,6 +996,8 @@ EXPORT_SYMBOL(padata_free);
  * padata_alloc_shell - Allocate and initialize padata shell.
  *
  * @pinst: Parent padata_instance object.
+ *
+ * Return: new shell on success, NULL on error
  */
 struct padata_shell *padata_alloc_shell(struct padata_instance *pinst)
 {