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

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Message-ID: <20170329105536.GH27994@dhcp22.suse.cz>
Date:   Wed, 29 Mar 2017 12:55:36 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Ilya Dryomov <idryomov@...il.com>
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>, linux-xfs@...r.kernel.org
Subject: Re: [PATCH 4.4 48/76] libceph: force GFP_NOIO for socket allocations

On Wed 29-03-17 12:41:26, Michal Hocko wrote:
[...]
> > ceph_con_workfn
> >   mutex_lock(&con->mutex)  # ceph_connection::mutex
> >   try_write
> >     ceph_tcp_connect
> >       sock_create_kern
> >         GFP_KERNEL allocation
> >           allocator recurses into XFS, more I/O is issued

One more note. So what happens if this is a GFP_NOIO request which
cannot make any progress? Your IO thread is blocked on con->mutex
as you write below but the above thread cannot proceed as well. So I am
_really_ not sure this acutally helps.

[...]
> > 
> > rbd_queue_workfn
> >   ceph_osdc_start_request
> >     mutex_lock(&osdc->request_mutex);
> >     ceph_con_send
> >       mutex_lock(&con->mutex)  # deadlock

-- 
Michal Hocko
SUSE Labs