workqueue: restore POOL_MANAGING_WORKERS (552a37e9) · Commits · 戴 / test

This patch restores POOL_MANAGING_WORKERS which was replaced by pool->manager_mutex by "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. Signed-off-by:

Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by:

Tejun Heo <tj@kernel.org>

kernel/workqueue.c

+4 −1

Original line number	Diff line number	Diff line
		@@ -66,6 +66,7 @@ enum {

		/* pool flags */
		POOL_MANAGE_WORKERS = 1 << 0, /* need to manage workers */
		POOL_MANAGING_WORKERS = 1 << 1, /* managing workers */

		/* worker flags */
		WORKER_STARTED = 1 << 0, /* started */
		@@ -652,7 +653,7 @@ static bool need_to_manage_workers(struct worker_pool *pool)
		/* Do we have too many workers and should some go away? */
		static bool too_many_workers(struct worker_pool *pool)
		{
		bool managing = mutex_is_locked(&pool->manager_mutex);
		bool managing = pool->flags & POOL_MANAGING_WORKERS;
		int nr_idle = pool->nr_idle + managing; /* manager is considered idle */
		int nr_busy = pool->nr_workers - nr_idle;

		@@ -1827,6 +1828,7 @@ static bool manage_workers(struct worker *worker)
		if (!mutex_trylock(&pool->manager_mutex))
		return ret;

		pool->flags \|= POOL_MANAGING_WORKERS;
		pool->flags &= ~POOL_MANAGE_WORKERS;

		/*
		@@ -1836,6 +1838,7 @@ static bool manage_workers(struct worker *worker)
		ret \|= maybe_destroy_workers(pool);
		ret \|= maybe_create_worker(pool);

		pool->flags &= ~POOL_MANAGING_WORKERS;
		mutex_unlock(&pool->manager_mutex);
		return ret;
		}

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