linux-kernel - Re: [PATCH 4.4 48/76] libceph: force GFP

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Date:   Tue, 28 Mar 2017 15:23:58 +0200
From:   Ilya Dryomov <idryomov@...il.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        stable@...r.kernel.org, Sergey Jerusalimov <wintchester@...il.com>,
        Jeff Layton <jlayton@...hat.com>
Subject: Re: [PATCH 4.4 48/76] libceph: force GFP_NOIO for socket allocations

On Tue, Mar 28, 2017 at 2:43 PM, Michal Hocko <mhocko@...nel.org> wrote:
> On Tue 28-03-17 14:30:45, Greg KH wrote:
>> 4.4-stable review patch.  If anyone has any objections, please let me know.
>
> I haven't seen the original patch but the changelog makes me worried.
> How exactly this is a problem? Where do we lockup? Does rbd/libceph take
> any xfs locks?

No, it doesn't.  This is just another instance of "using GFP_KERNEL on
the writeback path may lead to a deadlock" with nothing extra to it.

XFS is writing out data, libceph messenger worker tries to open
a socket and recurses back into XFS because the sockfs inode is
allocated with GFP_KERNEL.  The message with some of the data never
goes out and eventually we get a deadlock.

I've only included the offending stack trace.  I guess I should have
stressed that ceph-msgr workqueue is used for reclaim.

Thanks,

                Ilya