From: Tejun Heo <tj@kernel.org>
Date: Sun, 25 Dec 2011 13:29:14 +0000 (+0100)
Subject: block: an exiting task should be allowed to create io_context
X-Git-Tag: v3.3-rc1~49^2~2
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=fd63836811d6e5b5f5f608abf865bc9e91762c8c;p=pandora-kernel.git

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>
---

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