Hello, This is the preliminary patch that I have. I haven't tested it yet. Once testing is complete, I'll re-post with test results and apply the patch. Thanks and sorry about the trouble. ------ 8< ------ A worker_pool's forward progress is guaranteed by the fact that the last idle worker assumes the manager role to create more workers and summon the rescuers if creating workers doesn't succeed in timely manner before proceeding to execute work items. This manager role is implemented in manage_workers(), which indicates whether the worker may proceed to work item execution with its return value. This is necessary because multiple workers may contend for the manager role, and, if there already is a manager, others should proceed to work item execution. Unfortunately, the function also indicates that the worker may proceed to work item execution if need_to_create_worker() is false before releasing pool->lock. need_to_create_worker() tests the following conditions. pending work items && !nr_running && !nr_idle The first and third conditions are protected by pool->lock and thus won't change while holding pool->lock; however, nr_running can change asynchronously as other workers block and resume and while it's likely to be zero, as someone woke this worker up, some other workers could have become runnable inbetween making it non-zero. If this happens, manage_worker() could return false even with zero nr_idle making the worker, the last idle one, proceed to execute work items. If then all workers of the pool end up blocking on a resource which can only be released by a work item which is pending on that pool, the whole pool can deadlock as there's no one to create more workers or summon the rescuers. This patch fixes the problem by making manage_workers() return false iff there's already another manager, which ensures that the last worker doesn't start executing work items. Signed-off-by: Tejun Heo <tj@xxxxxxxxxx> Reported-by: Eric Sandeen <sandeen@xxxxxxxxxxx> Link: http://lkml.kernel.org/g/54B019F4.8030009@xxxxxxxxxxx Cc: Dave Chinner <david@xxxxxxxxxxxxx> Cc: Lai Jiangshan <laijs@xxxxxxxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx --- kernel/workqueue.c | 25 +++++++++---------------- 1 file changed, 9 insertions(+), 16 deletions(-) --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -1841,17 +1841,13 @@ static void pool_mayday_timeout(unsigned * spin_lock_irq(pool->lock) which may be released and regrabbed * multiple times. Does GFP_KERNEL allocations. Called only from * manager. - * - * Return: - * %false if no action was taken and pool->lock stayed locked, %true - * otherwise. */ -static bool maybe_create_worker(struct worker_pool *pool) +static void maybe_create_worker(struct worker_pool *pool) __releases(&pool->lock) __acquires(&pool->lock) { if (!need_to_create_worker(pool)) - return false; + return; restart: spin_unlock_irq(&pool->lock); @@ -1877,7 +1873,6 @@ restart: */ if (need_to_create_worker(pool)) goto restart; - return true; } /** @@ -1897,16 +1892,14 @@ restart: * multiple times. Does GFP_KERNEL allocations. * * Return: - * %false if the pool don't need management and the caller can safely start - * processing works, %true indicates that the function released pool->lock - * and reacquired it to perform some management function and that the - * conditions that the caller verified while holding the lock before - * calling the function might no longer be true. + * %false if the pool doesn't need management and the caller can safely + * start processing works, %true if management function was performed and + * the conditions that the caller verified before calling the function may + * no longer be true. */ static bool manage_workers(struct worker *worker) { struct worker_pool *pool = worker->pool; - bool ret = false; /* * Anyone who successfully grabs manager_arb wins the arbitration @@ -1919,12 +1912,12 @@ static bool manage_workers(struct worker * actual management, the pool may stall indefinitely. */ if (!mutex_trylock(&pool->manager_arb)) - return ret; + return false; - ret |= maybe_create_worker(pool); + maybe_create_worker(pool); mutex_unlock(&pool->manager_arb); - return ret; + return true; } /** _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
