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workqueue: update comments and a warning message

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* Update incorrect and add missing synchronization labels.

* Update incorrect or misleading comments.  Add new comments where
  clarification is necessary.  Reformat / rephrase some comments.

* drain_workqueue() can be used separately from destroy_workqueue()
  but its warning message was incorrectly referring to destruction.

Other than the warning message change, this patch doesn't make any
functional changes.

Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Tejun Heo 2013-03-13 16:51:36 -07:00
parent 983ca25e73
commit c5aa87bbf4
1 changed files with 44 additions and 40 deletions
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84
kernel/workqueue.c
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@ -145,7 +145,7 @@ struct worker_pool {
struct timer_list idle_timer; /* L: worker idle timeout */
struct timer_list mayday_timer; /* L: SOS timer for workers */
/* workers are chained either in busy_hash or idle_list */
/* a workers is either on busy_hash or idle_list, or the manager */
DECLARE_HASHTABLE(busy_hash, BUSY_WORKER_HASH_ORDER);
/* L: hash of busy workers */
@ -154,8 +154,8 @@ struct worker_pool {
struct ida worker_ida; /* L: for worker IDs */
struct workqueue_attrs *attrs; /* I: worker attributes */
struct hlist_node hash_node; /* R: unbound_pool_hash node */
int refcnt; /* refcnt for unbound pools */
struct hlist_node hash_node; /* W: unbound_pool_hash node */
int refcnt; /* W: refcnt for unbound pools */
/*
* The current concurrency level. As it's likely to be accessed
@ -213,8 +213,8 @@ struct wq_flusher {
struct wq_device;
/*
* The externally visible workqueue abstraction is an array of
* per-CPU workqueues:
* The externally visible workqueue. It relays the issued work items to
* the appropriate worker_pool through its pool_workqueues.
*/
struct workqueue_struct {
unsigned int flags; /* W: WQ_* flags */
@ -247,9 +247,10 @@ struct workqueue_struct {
static struct kmem_cache *pwq_cache;
/* hash of all unbound pools keyed by pool->attrs */
/* W: hash of all unbound pools keyed by pool->attrs */
static DEFINE_HASHTABLE(unbound_pool_hash, UNBOUND_POOL_HASH_ORDER);
/* I: attributes used when instantiating standard unbound pools on demand */
static struct workqueue_attrs *unbound_std_wq_attrs[NR_STD_WORKER_POOLS];
struct workqueue_struct *system_wq __read_mostly;
@ -434,16 +435,13 @@ static DEFINE_SPINLOCK(workqueue_lock);
static LIST_HEAD(workqueues);
static bool workqueue_freezing; /* W: have wqs started freezing? */
/*
* The CPU and unbound standard worker pools. The unbound ones have
* POOL_DISASSOCIATED set, and their workers have WORKER_UNBOUND set.
*/
/* the per-cpu worker pools */
static DEFINE_PER_CPU_SHARED_ALIGNED(struct worker_pool [NR_STD_WORKER_POOLS],
cpu_worker_pools);
/*
* idr of all pools. Modifications are protected by workqueue_lock. Read
* accesses are protected by sched-RCU protected.
* R: idr of all pools. Modifications are protected by workqueue_lock.
* Read accesses are protected by sched-RCU protected.
*/
static DEFINE_IDR(worker_pool_idr);
@ -890,13 +888,12 @@ static inline void worker_clr_flags(struct worker *worker, unsigned int flags)
* recycled work item as currently executing and make it wait until the
* current execution finishes, introducing an unwanted dependency.
*
* This function checks the work item address, work function and workqueue
* to avoid false positives. Note that this isn't complete as one may
* construct a work function which can introduce dependency onto itself
* through a recycled work item. Well, if somebody wants to shoot oneself
* in the foot that badly, there's only so much we can do, and if such
* deadlock actually occurs, it should be easy to locate the culprit work
* function.
* This function checks the work item address and work function to avoid
* false positives. Note that this isn't complete as one may construct a
* work function which can introduce dependency onto itself through a
* recycled work item. Well, if somebody wants to shoot oneself in the
* foot that badly, there's only so much we can do, and if such deadlock
* actually occurs, it should be easy to locate the culprit work function.
*
* CONTEXT:
* spin_lock_irq(pool->lock).
@ -1187,9 +1184,9 @@ static void insert_work(struct pool_workqueue *pwq, struct work_struct *work,
get_pwq(pwq);
/*
* Ensure either worker_sched_deactivated() sees the above
* list_add_tail() or we see zero nr_running to avoid workers
* lying around lazily while there are works to be processed.
* Ensure either wq_worker_sleeping() sees the above
* list_add_tail() or we see zero nr_running to avoid workers lying
* around lazily while there are works to be processed.
*/
smp_mb();
@ -1790,6 +1787,10 @@ static struct worker *create_worker(struct worker_pool *pool)
if (IS_ERR(worker->task))
goto fail;
/*
* set_cpus_allowed_ptr() will fail if the cpumask doesn't have any
* online CPUs. It'll be re-applied when any of the CPUs come up.
*/
set_user_nice(worker->task, pool->attrs->nice);
set_cpus_allowed_ptr(worker->task, pool->attrs->cpumask);
@ -1950,8 +1951,8 @@ static void pool_mayday_timeout(unsigned long __pool)
* sent to all rescuers with works scheduled on @pool to resolve
* possible allocation deadlock.
*
* On return, need_to_create_worker() is guaranteed to be false and
* may_start_working() true.
* On return, need_to_create_worker() is guaranteed to be %false and
* may_start_working() %true.
*
* LOCKING:
* spin_lock_irq(pool->lock) which may be released and regrabbed
@ -1959,7 +1960,7 @@ static void pool_mayday_timeout(unsigned long __pool)
* manager.
*
* RETURNS:
* false if no action was taken and pool->lock stayed locked, true
* %false if no action was taken and pool->lock stayed locked, %true
* otherwise.
*/
static bool maybe_create_worker(struct worker_pool *pool)
@ -2016,7 +2017,7 @@ restart:
* multiple times. Called only from manager.
*
* RETURNS:
* false if no action was taken and pool->lock stayed locked, true
* %false if no action was taken and pool->lock stayed locked, %true
* otherwise.
*/
static bool maybe_destroy_workers(struct worker_pool *pool)
@ -2268,11 +2269,11 @@ static void process_scheduled_works(struct worker *worker)
* worker_thread - the worker thread function
* @__worker: self
*
* The worker thread function. There are NR_CPU_WORKER_POOLS dynamic pools
* of these per each cpu. These workers process all works regardless of
* their specific target workqueue. The only exception is works which
* belong to workqueues with a rescuer which will be explained in
* rescuer_thread().
* The worker thread function. All workers belong to a worker_pool -
* either a per-cpu one or dynamic unbound one. These workers process all
* work items regardless of their specific target workqueue. The only
* exception is work items which belong to workqueues with a rescuer which
* will be explained in rescuer_thread().
*/
static int worker_thread(void *__worker)
{
@ -2600,11 +2601,8 @@ static bool flush_workqueue_prep_pwqs(struct workqueue_struct *wq,
* flush_workqueue - ensure that any scheduled work has run to completion.
* @wq: workqueue to flush
*
* Forces execution of the workqueue and blocks until its completion.
* This is typically used in driver shutdown handlers.
*
* We sleep until all works which were queued on entry have been handled,
* but we are not livelocked by new incoming ones.
* This function sleeps until all work items which were queued on entry
* have finished execution, but it is not livelocked by new incoming ones.
*/
void flush_workqueue(struct workqueue_struct *wq)
{
@ -2794,7 +2792,7 @@ reflush:
if (++flush_cnt == 10 ||
(flush_cnt % 100 == 0 && flush_cnt <= 1000))
pr_warn("workqueue %s: flush on destruction isn't complete after %u tries\n",
pr_warn("workqueue %s: drain_workqueue() isn't complete after %u tries\n",
wq->name, flush_cnt);
local_irq_enable();
@ -3576,7 +3574,9 @@ static void rcu_free_pool(struct rcu_head *rcu)
* @pool: worker_pool to put
*
* Put @pool. If its refcnt reaches zero, it gets destroyed in sched-RCU
* safe manner.
* safe manner. get_unbound_pool() calls this function on its failure path
* and this function should be able to release pools which went through,
* successfully or not, init_worker_pool().
*/
static void put_unbound_pool(struct worker_pool *pool)
{
@ -3602,7 +3602,11 @@ static void put_unbound_pool(struct worker_pool *pool)
spin_unlock_irq(&workqueue_lock);
/* lock out manager and destroy all workers */
/*
* Become the manager and destroy all workers. Grabbing
* manager_arb prevents @pool's workers from blocking on
* manager_mutex.
*/
mutex_lock(&pool->manager_arb);
spin_lock_irq(&pool->lock);
@ -4339,7 +4343,7 @@ EXPORT_SYMBOL_GPL(work_on_cpu);
* freeze_workqueues_begin - begin freezing workqueues
*
* Start freezing workqueues. After this function returns, all freezable
* workqueues will queue new works to their frozen_works list instead of
* workqueues will queue new works to their delayed_works list instead of
* pool->worklist.
*
* CONTEXT: