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workqueue: restore POOL_MANAGING_WORKERS

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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.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Lai Jiangshan 2012-09-10 10:03:33 -07:00 committed by Tejun Heo
parent ec58815ab0
commit 552a37e936
1 changed files with 4 additions and 1 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

5
kernel/workqueue.c
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@ -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;
}