From bc1ecc65a259fa9333dc8bd6a4ba0cf03b7d4bf8 Mon Sep 17 00:00:00 2001
From: Ilya Dryomov <ilya.dryomov@inktank.com>
Date: Mon, 4 Aug 2014 18:04:39 +0400
Subject: [PATCH] rbd: rework rbd_request_fn()

While it was never a good idea to sleep in request_fn(), commit
34c6bc2c919a ("locking/mutexes: Add extra reschedule point") made it
a *bad* idea.  mutex_lock() since 3.15 may reschedule *before* putting
task on the mutex wait queue, which for tasks in !TASK_RUNNING state
means block forever.  request_fn() may be called with !TASK_RUNNING on
the way to schedule() in io_schedule().

Offload request handling to a workqueue, one per rbd device, to avoid
calling blocking primitives from rbd_request_fn().

Fixes: http://tracker.ceph.com/issues/8818

Cc: stable@vger.kernel.org # 3.16, needs backporting for 3.15
Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com>
Tested-by: Eric Eastman <eric0e@aol.com>
Tested-by: Greg Wilson <greg.wilson@keepertech.com>
Reviewed-by: Alex Elder <elder@linaro.org>
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