* [PATCH] workqueue: make manage_workers() and pool destruction exclusive
@ 2018-03-19 7:35 Lai Jiangshan
2018-03-19 15:27 ` Tejun Heo
0 siblings, 1 reply; 2+ messages in thread
From: Lai Jiangshan @ 2018-03-19 7:35 UTC (permalink / raw)
To: linux-kernel; +Cc: Lai Jiangshan, Tejun Heo
The original code allows destroying the pool when the pool
is still active in manage_workers(). A synchronization
mechanism between manage_workers() and pool destruction
was added for protection.
This patch simply makes manage_workers() and pool destruction
exclusive by getting an indirect refcount of the pool in
manage_workers(). "indirect" means it gets a refcount of
the first involved pwq which holds a refcount of the pool.
This refcount can prevent the pool from being destroyed.
The original synchronization mechanism (wq_manager_wait)
is also removed.
Signed-off-by: Lai Jiangshan <jiangshanlai@gmail.com>
---
kernel/workqueue.c | 21 ++++++++++-----------
1 file changed, 10 insertions(+), 11 deletions(-)
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index bb9a519cbf50..316dbed5f40c 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -300,7 +300,6 @@ static struct workqueue_attrs *wq_update_unbound_numa_attrs_buf;
static DEFINE_MUTEX(wq_pool_mutex); /* protects pools and workqueues list */
static DEFINE_SPINLOCK(wq_mayday_lock); /* protects wq->maydays list */
-static DECLARE_WAIT_QUEUE_HEAD(wq_manager_wait); /* wait for manager to go away */
static LIST_HEAD(workqueues); /* PR: list of all workqueues */
static bool workqueue_freezing; /* PL: have wqs started freezing? */
@@ -1980,10 +1979,18 @@ __acquires(&pool->lock)
static bool manage_workers(struct worker *worker)
{
struct worker_pool *pool = worker->pool;
+ struct pool_workqueue *pwq;
if (pool->flags & POOL_MANAGER_ACTIVE)
return false;
+ /*
+ * Get a refcount of the pwq which holds a refcount of the pool
+ * to prevent the pool from being destroyed.
+ */
+ pwq = get_work_pwq(list_first_entry(&pool->worklist,
+ struct work_struct, entry));
+ get_pwq(pwq);
pool->flags |= POOL_MANAGER_ACTIVE;
pool->manager = worker;
@@ -1991,7 +1998,7 @@ static bool manage_workers(struct worker *worker)
pool->manager = NULL;
pool->flags &= ~POOL_MANAGER_ACTIVE;
- wake_up(&wq_manager_wait);
+ put_pwq(pwq);
return true;
}
@@ -3295,16 +3302,8 @@ static void put_unbound_pool(struct worker_pool *pool)
idr_remove(&worker_pool_idr, pool->id);
hash_del(&pool->hash_node);
- /*
- * Become the manager and destroy all workers. This prevents
- * @pool's workers from blocking on attach_mutex. We're the last
- * manager and @pool gets freed with the flag set.
- */
spin_lock_irq(&pool->lock);
- wait_event_lock_irq(wq_manager_wait,
- !(pool->flags & POOL_MANAGER_ACTIVE), pool->lock);
- pool->flags |= POOL_MANAGER_ACTIVE;
-
+ WARN_ON(pool->nr_workers != pool->nr_idle);
while ((worker = first_idle_worker(pool)))
destroy_worker(worker);
WARN_ON(pool->nr_workers || pool->nr_idle);
--
2.14.3 (Apple Git-98)
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] workqueue: make manage_workers() and pool destruction exclusive
2018-03-19 7:35 [PATCH] workqueue: make manage_workers() and pool destruction exclusive Lai Jiangshan
@ 2018-03-19 15:27 ` Tejun Heo
0 siblings, 0 replies; 2+ messages in thread
From: Tejun Heo @ 2018-03-19 15:27 UTC (permalink / raw)
To: Lai Jiangshan; +Cc: linux-kernel
On Mon, Mar 19, 2018 at 03:35:07PM +0800, Lai Jiangshan wrote:
> The original code allows destroying the pool when the pool
> is still active in manage_workers(). A synchronization
> mechanism between manage_workers() and pool destruction
> was added for protection.
>
> This patch simply makes manage_workers() and pool destruction
> exclusive by getting an indirect refcount of the pool in
> manage_workers(). "indirect" means it gets a refcount of
> the first involved pwq which holds a refcount of the pool.
> This refcount can prevent the pool from being destroyed.
>
> The original synchronization mechanism (wq_manager_wait)
> is also removed.
Hmm... idk, this is more indirect and subtle than the existing code
and it's not like the existing code was overly complicated.
Thanks.
--
tejun
^ permalink raw reply [flat|nested] 2+ messages in thread
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