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authorTejun Heo <tj@kernel.org>2011-12-25 14:29:14 +0100
committerJens Axboe <axboe@kernel.dk>2011-12-25 14:29:14 +0100
commitfd63836811d6e5b5f5f608abf865bc9e91762c8c (patch)
tree9262ccdc0319b331c497701a851c8c5752dedb00 /block
parent64c42998f14d5894ea3138625897d620b30c8e4e (diff)
downloadlinux-linaro-stable-fd63836811d6e5b5f5f608abf865bc9e91762c8c.tar.gz
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')
-rw-r--r--block/blk-ioc.c11
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);