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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>
hifive-unleashed-5.1
Tejun Heo 2011-12-25 14:29:14 +01:00 committed by Jens Axboe
parent 64c42998f1
commit fd63836811
1 changed files with 9 additions and 2 deletions
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11
block/blk-ioc.c
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@ -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);