workqueue: restore POOL_MANAGING_WORKERS

This patch restores POOL_MANAGING_WORKERS which was replaced by pool->manager_mutex by 6037315269 "workqueue: use mutex for global_cwq manager exclusion". There's a subtle idle worker depletion bug across CPU hotplug events and we need to distinguish an actual manager and CPU hotplug preventing management. POOL_MANAGING_WORKERS will be used for the former and manager_mutex the later. This patch just lays POOL_MANAGING_WORKERS on top of the existing manager_mutex and doesn't introduce any synchronization changes. The next patch will update it. Note that this patch fixes a non-critical anomaly where too_many_workers() may return %true spuriously while CPU hotplug is in progress. While the issue could schedule idle timer spuriously, it didn't trigger any actual misbehavior. tj: Rewrote patch description.

Lai Jiangshan committed 14 years ago

Commit 552a37e1 parent ec588151 file · +4 −1Browse files

Showing the changes to kernel/workqueue.c (1 of 1 file). Show all

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kernel/workqueue.c+4−1

@@ -66,6 +66,7 @@ enum { · 65 unmodified lines
66	66
67	67	/* pool flags */
68	68	POOL_MANAGE_WORKERS = 1 << 0, /* need to manage workers */
	69	+ POOL_MANAGING_WORKERS = 1 << 1, /* managing workers */
69	70
70	71	/* worker flags */
71	72	WORKER_STARTED = 1 << 0, /* started */
@@ -652,7 +653,7 @@ static bool need_to_manage_workers(struct worker_pool *pool) · 580 unmodified lines
652	653	/* Do we have too many workers and should some go away? */
653	654	static bool too_many_workers(struct worker_pool *pool)
654	655	{
655		− bool managing = mutex_is_locked(&pool->manager_mutex);
	656	+ bool managing = pool->flags & POOL_MANAGING_WORKERS;
656	657	int nr_idle = pool->nr_idle + managing; /* manager is considered idle */
657	658	int nr_busy = pool->nr_workers - nr_idle;
658	659
@@ -1827,6 +1828,7 @@ static bool manage_workers(struct worker *worker) · 1168 unmodified lines
1827	1828	if (!mutex_trylock(&pool->manager_mutex))
1828	1829	return ret;
1829	1830
	1831	+ pool->flags \|= POOL_MANAGING_WORKERS;
1830	1832	pool->flags &= ~POOL_MANAGE_WORKERS;
1831	1833
1832	1834	/*
@@ -1836,6 +1838,7 @@ static bool manage_workers(struct worker *worker) · 3 unmodified lines
1836	1838	ret \|= maybe_destroy_workers(pool);
1837	1839	ret \|= maybe_create_worker(pool);
1838	1840
	1841	+ pool->flags &= ~POOL_MANAGING_WORKERS;
1839	1842	mutex_unlock(&pool->manager_mutex);
1840	1843	return ret;
1841	1844	}