POOL_MANAGING_WORKERS is used to synchronize the manager role. Synchronizing among workers doesn't need blocking and that's why it's implemented as a flag.
It got converted to a mutex a while back to add blocking wait from CPU hotplug path - 6037315269 ("workqueue: use mutex for global_cwq manager exclusion"). Later it turned out that synchronization among workers and cpu hotplug need to be done separately. Eventually, POOL_MANAGING_WORKERS is restored and workqueue->manager_mutex got morphed into workqueue->assoc_mutex - 552a37e936 ("workqueue: restore POOL_MANAGING_WORKERS") and b2eb83d123 ("workqueue: rename manager_mutex to assoc_mutex"). Now, we're gonna need to be able to lock out managers from destroy_workqueue() to support multiple unbound pools with custom attributes making it again necessary to be able to block on the manager role. This patch replaces POOL_MANAGING_WORKERS with worker_pool->manager_mutex. This patch doesn't introduce any behavior changes. Signed-off-by: Tejun Heo <t...@kernel.org> --- kernel/workqueue.c | 13 ++++++------- 1 file changed, 6 insertions(+), 7 deletions(-) diff --git a/kernel/workqueue.c b/kernel/workqueue.c index 2645218..68b3443 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -64,7 +64,6 @@ enum { * create_worker() is in progress. */ POOL_MANAGE_WORKERS = 1 << 0, /* need to manage workers */ - POOL_MANAGING_WORKERS = 1 << 1, /* managing workers */ POOL_DISASSOCIATED = 1 << 2, /* cpu can't serve workers */ POOL_FREEZING = 1 << 3, /* freeze in progress */ @@ -145,6 +144,7 @@ struct worker_pool { DECLARE_HASHTABLE(busy_hash, BUSY_WORKER_HASH_ORDER); /* L: hash of busy workers */ + struct mutex manager_mutex; /* the holder is the manager */ struct mutex assoc_mutex; /* protect POOL_DISASSOCIATED */ struct ida worker_ida; /* L: for worker IDs */ @@ -702,7 +702,7 @@ 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 = pool->flags & POOL_MANAGING_WORKERS; + bool managing = mutex_is_locked(&pool->manager_mutex); int nr_idle = pool->nr_idle + managing; /* manager is considered idle */ int nr_busy = pool->nr_workers - nr_idle; @@ -2027,15 +2027,13 @@ static bool manage_workers(struct worker *worker) struct worker_pool *pool = worker->pool; bool ret = false; - if (pool->flags & POOL_MANAGING_WORKERS) + if (!mutex_trylock(&pool->manager_mutex)) return ret; - pool->flags |= POOL_MANAGING_WORKERS; - /* * To simplify both worker management and CPU hotplug, hold off * management while hotplug is in progress. CPU hotplug path can't - * grab %POOL_MANAGING_WORKERS to achieve this because that can + * grab @pool->manager_mutex to achieve this because that can * lead to idle worker depletion (all become busy thinking someone * else is managing) which in turn can result in deadlock under * extreme circumstances. Use @pool->assoc_mutex to synchronize @@ -2075,8 +2073,8 @@ 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->assoc_mutex); + mutex_unlock(&pool->manager_mutex); return ret; } @@ -3805,6 +3803,7 @@ static int __init init_workqueues(void) setup_timer(&pool->mayday_timer, pool_mayday_timeout, (unsigned long)pool); + mutex_init(&pool->manager_mutex); mutex_init(&pool->assoc_mutex); ida_init(&pool->worker_ida); -- 1.8.1.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/