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| author | Tejun Heo <tj@kernel.org> | 2011-12-25 14:29:14 +0100 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2011-12-25 14:29:14 +0100 |
| commit | fd63836811d6e5b5f5f608abf865bc9e91762c8c (patch) | |
| tree | 9262ccdc0319b331c497701a851c8c5752dedb00 /block/blk-ioc.c | |
| parent | 64c42998f14d5894ea3138625897d620b30c8e4e (diff) | |
| download | linux-fd63836811d6e5b5f5f608abf865bc9e91762c8c.tar.gz linux-fd63836811d6e5b5f5f608abf865bc9e91762c8c.tar.bz2 linux-fd63836811d6e5b5f5f608abf865bc9e91762c8c.zip | |
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 <tj@kernel.org>
Reported-by: Andrew Morton <akpm@linux-foundation.org>
Reported-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block/blk-ioc.c')
| -rw-r--r-- | block/blk-ioc.c | 11 |
1 files changed, 9 insertions, 2 deletions
diff --git a/block/blk-ioc.c b/block/blk-ioc.c index ce9b35a9468e..33fae7df16a0 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); |