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workqueue: protect wq->pwqs and iteration with wq->mutex 

We're expanding wq->mutex to cover all fields specific to each
workqueue with the end goal of replacing pwq_lock which will make
locking simpler and easier to understand.

init_and_link_pwq() and pwq_unbound_release_workfn() already grab
wq->mutex when adding or removing a pwq from wq->pwqs list.  This
patch makes it official that the list is wq->mutex protected for
writes and updates readers accoridingly.  Explicit IRQ toggles for
sched-RCU read-locking in flush_workqueue_prep_pwqs() and
drain_workqueues() are removed as the surrounding wq->mutex can
provide sufficient synchronization.

Also, assert_rcu_or_pwq_lock() is renamed to assert_rcu_or_wq_mutex()
and checks for wq->mutex too.

pwq_lock locking and assertion are not removed by this patch and a
couple of for_each_pwq() iterations are still protected by it.
They'll be removed by future patches.

tj: Rebased on top of the current dev branch.  Updated description.
    Folded in assert_rcu_or_wq_mutex() renaming from a later patch
    along with associated comment updates.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Lai Jiangshan 2013-03-25 16:57:18 -07:00 committed by Tejun Heo
parent 87fc741e94
commit b09f4fd39c
1 changed files with 18 additions and 24 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

42
kernel/workqueue.c
View File

@ -204,7 +204,7 @@ struct pool_workqueue {
* Release of unbound pwq is punted to system_wq. See put_pwq()
* and pwq_unbound_release_workfn() for details. pool_workqueue
* itself is also sched-RCU protected so that the first pwq can be
* determined without grabbing pwq_lock.
* determined without grabbing wq->mutex.
*/
struct work_struct unbound_release_work;
struct rcu_head rcu;
@ -298,10 +298,11 @@ static void copy_workqueue_attrs(struct workqueue_attrs *to,
lockdep_is_held(&wq_pool_mutex), \
"sched RCU or wq_pool_mutex should be held")
#define assert_rcu_or_pwq_lock() \
#define assert_rcu_or_wq_mutex(wq) \
rcu_lockdep_assert(rcu_read_lock_sched_held() || \
lockdep_is_held(&wq->mutex) || \
lockdep_is_held(&pwq_lock), \
"sched RCU or pwq_lock should be held")
"sched RCU or wq->mutex should be held")
#ifdef CONFIG_LOCKDEP
#define assert_manager_or_pool_lock(pool) \
@ -356,7 +357,7 @@ static void copy_workqueue_attrs(struct workqueue_attrs *to,
* @pwq: iteration cursor
* @wq: the target workqueue
*
* This must be called either with pwq_lock held or sched RCU read locked.
* This must be called either with wq->mutex held or sched RCU read locked.
* If the pwq needs to be used beyond the locking in effect, the caller is
* responsible for guaranteeing that the pwq stays online.
*
@ -365,7 +366,7 @@ static void copy_workqueue_attrs(struct workqueue_attrs *to,
*/
#define for_each_pwq(pwq, wq) \
list_for_each_entry_rcu((pwq), &(wq)->pwqs, pwqs_node) \
if (({ assert_rcu_or_pwq_lock(); false; })) { } \
if (({ assert_rcu_or_wq_mutex(wq); false; })) { } \
else
#ifdef CONFIG_DEBUG_OBJECTS_WORK
@ -504,13 +505,13 @@ static int worker_pool_assign_id(struct worker_pool *pool)
* first_pwq - return the first pool_workqueue of the specified workqueue
* @wq: the target workqueue
*
* This must be called either with pwq_lock held or sched RCU read locked.
* This must be called either with wq->mutex held or sched RCU read locked.
* If the pwq needs to be used beyond the locking in effect, the caller is
* responsible for guaranteeing that the pwq stays online.
*/
static struct pool_workqueue *first_pwq(struct workqueue_struct *wq)
{
assert_rcu_or_pwq_lock();
assert_rcu_or_wq_mutex(wq);
return list_first_or_null_rcu(&wq->pwqs, struct pool_workqueue,
pwqs_node);
}
@ -2477,12 +2478,10 @@ static bool flush_workqueue_prep_pwqs(struct workqueue_struct *wq,
atomic_set(&wq->nr_pwqs_to_flush, 1);
}
local_irq_disable();
for_each_pwq(pwq, wq) {
struct worker_pool *pool = pwq->pool;
spin_lock(&pool->lock);
spin_lock_irq(&pool->lock);
if (flush_color >= 0) {
WARN_ON_ONCE(pwq->flush_color != -1);
@ -2499,11 +2498,9 @@ static bool flush_workqueue_prep_pwqs(struct workqueue_struct *wq,
pwq->work_color = work_color;
}
spin_unlock(&pool->lock);
spin_unlock_irq(&pool->lock);
}
local_irq_enable();
if (flush_color >= 0 && atomic_dec_and_test(&wq->nr_pwqs_to_flush))
complete(&wq->first_flusher->done);
@ -2691,14 +2688,14 @@ void drain_workqueue(struct workqueue_struct *wq)
reflush:
flush_workqueue(wq);
local_irq_disable();
mutex_lock(&wq->mutex);
for_each_pwq(pwq, wq) {
bool drained;
spin_lock(&pwq->pool->lock);
spin_lock_irq(&pwq->pool->lock);
drained = !pwq->nr_active && list_empty(&pwq->delayed_works);
spin_unlock(&pwq->pool->lock);
spin_unlock_irq(&pwq->pool->lock);
if (drained)
continue;
@ -2708,13 +2705,10 @@ reflush:
pr_warn("workqueue %s: drain_workqueue() isn't complete after %u tries\n",
wq->name, flush_cnt);
local_irq_enable();
mutex_unlock(&wq->mutex);
goto reflush;
}
local_irq_enable();
mutex_lock(&wq->mutex);
if (!--wq->nr_drainers)
wq->flags &= ~__WQ_DRAINING;
mutex_unlock(&wq->mutex);
@ -3843,13 +3837,13 @@ void destroy_workqueue(struct workqueue_struct *wq)
drain_workqueue(wq);
/* sanity checks */
spin_lock_irq(&pwq_lock);
mutex_lock(&wq->mutex);
for_each_pwq(pwq, wq) {
int i;
for (i = 0; i < WORK_NR_COLORS; i++) {
if (WARN_ON(pwq->nr_in_flight[i])) {
spin_unlock_irq(&pwq_lock);
mutex_unlock(&wq->mutex);
return;
}
}
@ -3857,11 +3851,11 @@ void destroy_workqueue(struct workqueue_struct *wq)
if (WARN_ON(pwq->refcnt > 1) ||
WARN_ON(pwq->nr_active) ||
WARN_ON(!list_empty(&pwq->delayed_works))) {
spin_unlock_irq(&pwq_lock);
mutex_unlock(&wq->mutex);
return;
}
}
spin_unlock_irq(&pwq_lock);
mutex_unlock(&wq->mutex);
/*
* wq list is used to freeze wq, remove from list after