linux-kernel - Re: possible deadlock in generic_file_write

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Message-ID: <20171106133304.GS21978@ZenIV.linux.org.uk>
Date:   Mon, 6 Nov 2017 13:33:04 +0000
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Jan Kara <jack@...e.cz>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        syzbot 
        <bot+f99f3a0db9007f4f4e32db54229a240c4fe57c15@...kaller.appspotmail.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>, jlayton@...hat.com,
        LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
        npiggin@...il.com, rgoldwyn@...e.com, ross.zwisler@...ux.intel.com,
        syzkaller-bugs@...glegroups.com
Subject: Re: possible deadlock in generic_file_write_iter

On Mon, Nov 06, 2017 at 02:15:44PM +0100, Jan Kara wrote:

> > Should we annotate these inodes with different lock types? Or use
> > nesting annotations?
> 
> Well, you'd need to have a completely separate set of locking classes for
> each filesystem to avoid false positives like these. And that would
> increase number of classes lockdep has to handle significantly. So I'm not
> sure it's really worth it...

Especially when you consider that backing file might be on a filesystem
that lives on another loop device.  *All* per-{device,fs} locks involved
would need classes split that way...