[Ocfs2-devel] [PATCH 1/4] ocfs2: fix ip_unaligned_aio deadlock with dio work queue

From: Andrew Morton <akpm@linux-foundation.org>
To: ocfs2-devel@oss.oracle.com
Subject: [Ocfs2-devel] [PATCH 1/4] ocfs2: fix ip_unaligned_aio deadlock with dio work queue
Date: Mon, 23 Nov 2015 16:26:40 -0800	[thread overview]
Message-ID: <20151123162640.fa62db07934ad869b00e5435@linux-foundation.org> (raw)
In-Reply-To: <1448007799-10914-1-git-send-email-ryan.ding@oracle.com>

On Fri, 20 Nov 2015 16:23:16 +0800 Ryan Ding <ryan.ding@oracle.com> wrote:

> In the current implementation of unaligned aio+dio, lock order behave as follow:
> 
> in user process context:
>   -> call io_submit()
>     -> get i_mutex
> 		<== window1
>       -> get ip_unaligned_aio
>         -> submit direct io to block device
>     -> release i_mutex
>   -> io_submit() return
> 
> in dio work queue context(the work queue is created in __blockdev_direct_IO):
>   -> release ip_unaligned_aio
> 		<== window2
>     -> get i_mutex
>       -> clear unwritten flag & change i_size
>     -> release i_mutex
> 
> There is a limitation to the thread number of dio work queue. 256 at default.
> If all 256 thread are in the above 'window2' stage, and there is a user process
> in the 'window1' stage, the system will became deadlock. Since the user process
> hold i_mutex to wait ip_unaligned_aio lock, while there is a direct bio hold
> ip_unaligned_aio mutex who is waiting for a dio work queue thread to be
> schedule. But all the dio work queue thread is waiting for i_mutex lock in
> 'window2'.
> 
> This case only happened in a test which send a large number(more than 256) of
> aio at one io_submit() call.
> 
> My design is to remove ip_unaligned_aio lock. Change it to a sync io instead.
> Just like ip_unaligned_aio lock, serialize the unaligned aio dio.

So this patch series is a bunch of fixes against your previous patch series:

ocfs2-add-ocfs2_write_type_t-type-to-identify-the-caller-of-write.patch
ocfs2-use-c_new-to-indicate-newly-allocated-extents.patch
ocfs2-test-target-page-before-change-it.patch
ocfs2-do-not-change-i_size-in-write_end-for-direct-io.patch
ocfs2-return-the-physical-address-in-ocfs2_write_cluster.patch
ocfs2-record-unwritten-extents-when-populate-write-desc.patch
ocfs2-fix-sparse-file-data-ordering-issue-in-direct-io.patch
ocfs2-code-clean-up-for-direct-io.patch

correct?

Those patches are languishing a bit, awaiting review/ack.  I'll send
everything out for a round of review soon...