From fd63836811d6e5b5f5f608abf865bc9e91762c8c Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Sun, 25 Dec 2011 14:29:14 +0100 Subject: [PATCH] block: an exiting task should be allowed to create io_context While fixing io_context creation / task exit race condition, 6e736be7f2 "block: make ioc get/put interface more conventional and fix race on alloction" also prevented an exiting (%PF_EXITING) task from creating its own io_context. This is incorrect as exit path may issue IOs, e.g. from exit_files(), and if those IOs are the first ones issued by the task, io_context needs to be created to process the IOs. Combined with the existing problem of io_context / io_cq creation failure having the possibility of stalling IO, this problem results in deterministic full IO lockup with certain workloads. Fix it by allowing io_context creation regardless of %PF_EXITING for %current. Signed-off-by: Tejun Heo Reported-by: Andrew Morton Reported-by: Hugh Dickins Signed-off-by: Jens Axboe --- block/blk-ioc.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/block/blk-ioc.c b/block/blk-ioc.c index ce9b35a9468eb3..33fae7df16a016 100644 --- a/block/blk-ioc.c +++ b/block/blk-ioc.c @@ -281,9 +281,16 @@ void create_io_context_slowpath(struct task_struct *task, gfp_t gfp_flags, INIT_HLIST_HEAD(&ioc->icq_list); INIT_WORK(&ioc->release_work, ioc_release_fn); - /* try to install, somebody might already have beaten us to it */ + /* + * Try to install. ioc shouldn't be installed if someone else + * already did or @task, which isn't %current, is exiting. Note + * that we need to allow ioc creation on exiting %current as exit + * path may issue IOs from e.g. exit_files(). The exit path is + * responsible for not issuing IO after exit_io_context(). + */ task_lock(task); - if (!task->io_context && !(task->flags & PF_EXITING)) + if (!task->io_context && + (task == current || !(task->flags & PF_EXITING))) task->io_context = ioc; else kmem_cache_free(iocontext_cachep, ioc);