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authorTejun Heo <tj@kernel.org>2023-08-07 15:57:23 -1000
committerTejun Heo <tj@kernel.org>2023-08-07 15:57:23 -1000
commit967b494e2fd143a9c1a3201422aceadb5fa9fbfc (patch)
tree896fa6d0a2c178c6b8b1abab214b812cc04e3af0 /kernel/workqueue.c
parentfcecfa8f271acdf130acbb30842e7848a138af0f (diff)
workqueue: Use a kthread_worker to release pool_workqueues
pool_workqueue release path is currently bounced to system_wq; however, this is a bit tricky because this bouncing occurs while holding a pool lock and thus has risk of causing a A-A deadlock. This is currently addressed by the fact that only unbound workqueues use this bouncing path and system_wq is a per-cpu workqueue. While this works, it's brittle and requires a work-around like setting the lockdep subclass for the lock of unbound pools. Besides, future changes will use the bouncing path for per-cpu workqueues too making the current approach unusable. Let's just use a dedicated kthread_worker to untangle the dependency. This is just one more kthread for all workqueues and makes the pwq release logic simpler and more robust. Signed-off-by: Tejun Heo <tj@kernel.org>
Diffstat (limited to 'kernel/workqueue.c')
-rw-r--r--kernel/workqueue.c40
1 files changed, 23 insertions, 17 deletions
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 4347f493eca1..01bf22c5d515 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -257,12 +257,12 @@ struct pool_workqueue {
u64 stats[PWQ_NR_STATS];
/*
- * Release of unbound pwq is punted to system_wq. See put_pwq()
- * and pwq_unbound_release_workfn() for details. pool_workqueue
- * itself is also RCU protected so that the first pwq can be
- * determined without grabbing wq->mutex.
+ * Release of unbound pwq is punted to a kthread_worker. See put_pwq()
+ * and pwq_unbound_release_workfn() for details. pool_workqueue itself
+ * is also RCU protected so that the first pwq can be determined without
+ * grabbing wq->mutex.
*/
- struct work_struct unbound_release_work;
+ struct kthread_work unbound_release_work;
struct rcu_head rcu;
} __aligned(1 << WORK_STRUCT_FLAG_BITS);
@@ -395,6 +395,13 @@ static struct workqueue_attrs *unbound_std_wq_attrs[NR_STD_WORKER_POOLS];
/* I: attributes used when instantiating ordered pools on demand */
static struct workqueue_attrs *ordered_wq_attrs[NR_STD_WORKER_POOLS];
+/*
+ * I: kthread_worker to release pwq's. pwq release needs to be bounced to a
+ * process context while holding a pool lock. Bounce to a dedicated kthread
+ * worker to avoid A-A deadlocks.
+ */
+static struct kthread_worker *pwq_release_worker;
+
struct workqueue_struct *system_wq __read_mostly;
EXPORT_SYMBOL(system_wq);
struct workqueue_struct *system_highpri_wq __read_mostly;
@@ -1366,14 +1373,10 @@ static void put_pwq(struct pool_workqueue *pwq)
if (WARN_ON_ONCE(!(pwq->wq->flags & WQ_UNBOUND)))
return;
/*
- * @pwq can't be released under pool->lock, bounce to
- * pwq_unbound_release_workfn(). This never recurses on the same
- * pool->lock as this path is taken only for unbound workqueues and
- * the release work item is scheduled on a per-cpu workqueue. To
- * avoid lockdep warning, unbound pool->locks are given lockdep
- * subclass of 1 in get_unbound_pool().
+ * @pwq can't be released under pool->lock, bounce to a dedicated
+ * kthread_worker to avoid A-A deadlocks.
*/
- schedule_work(&pwq->unbound_release_work);
+ kthread_queue_work(pwq_release_worker, &pwq->unbound_release_work);
}
/**
@@ -3965,7 +3968,6 @@ static struct worker_pool *get_unbound_pool(const struct workqueue_attrs *attrs)
if (!pool || init_worker_pool(pool) < 0)
goto fail;
- lockdep_set_subclass(&pool->lock, 1); /* see put_pwq() */
copy_workqueue_attrs(pool->attrs, attrs);
pool->node = target_node;
@@ -3999,10 +4001,10 @@ static void rcu_free_pwq(struct rcu_head *rcu)
}
/*
- * Scheduled on system_wq by put_pwq() when an unbound pwq hits zero refcnt
- * and needs to be destroyed.
+ * Scheduled on pwq_release_worker by put_pwq() when an unbound pwq hits zero
+ * refcnt and needs to be destroyed.
*/
-static void pwq_unbound_release_workfn(struct work_struct *work)
+static void pwq_unbound_release_workfn(struct kthread_work *work)
{
struct pool_workqueue *pwq = container_of(work, struct pool_workqueue,
unbound_release_work);
@@ -4110,7 +4112,8 @@ static void init_pwq(struct pool_workqueue *pwq, struct workqueue_struct *wq,
INIT_LIST_HEAD(&pwq->inactive_works);
INIT_LIST_HEAD(&pwq->pwqs_node);
INIT_LIST_HEAD(&pwq->mayday_node);
- INIT_WORK(&pwq->unbound_release_work, pwq_unbound_release_workfn);
+ kthread_init_work(&pwq->unbound_release_work,
+ pwq_unbound_release_workfn);
}
/* sync @pwq with the current state of its associated wq and link it */
@@ -6433,6 +6436,9 @@ static void __init wq_cpu_intensive_thresh_init(void)
if (wq_cpu_intensive_thresh_us != ULONG_MAX)
return;
+ pwq_release_worker = kthread_create_worker(0, "pool_workqueue_release");
+ BUG_ON(IS_ERR(pwq_release_worker));
+
/*
* The default of 10ms is derived from the fact that most modern (as of
* 2023) processors can do a lot in 10ms and that it's just below what