linux-kernel - Re: possible deadlock in shmem

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Message-ID: <CAJuCfpFFCtmbvjLWDLZ9_bpNq-iT2+1cfdkpEcGV5tFCnbd+5g@mail.gmail.com>
Date:   Wed, 15 Jul 2020 19:49:52 -0700
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Todd Kjos <tkjos@...gle.com>, Hridya Valsaraju <hridya@...gle.com>,
        Hillf Danton <hdanton@...a.com>,
        Eric Biggers <ebiggers@...nel.org>,
        syzbot <syzbot+7a0d9d0b26efefe61780@...kaller.appspotmail.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Arve Hjønnevåg <arve@...roid.com>,
        Christian Brauner <christian@...uner.io>,
        "open list:ANDROID DRIVERS" <devel@...verdev.osuosl.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Hugh Dickins <hughd@...gle.com>,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>, Martijn Coenen <maco@...roid.com>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Todd Kjos <tkjos@...roid.com>,
        Markus Elfring <Markus.Elfring@....de>
Subject: Re: possible deadlock in shmem_fallocate (4)

On Tue, Jul 14, 2020 at 11:36 PM Michal Hocko <mhocko@...nel.org> wrote:
>
> On Tue 14-07-20 10:32:20, Suren Baghdasaryan wrote:
> [...]
> > I'm not sure how we can annotate the fact that the inode_lock in
> > generic_file_write_iter and in shmem_fallocate always operate on
> > different inodes. Ideas?
>
> I believe that the standard way is to use lockdep_set_class on your
> backing inode. But asking lockdep experts would be better than relying
> on my vague recollection

Thanks Michal! I think https://lkml.org/lkml/2020/7/15/1390 should fix
it, however I was unable to reproduce the lockdep warning to confirm
that this warning gets fixed by the patch.

>
> --
> Michal Hocko
> SUSE Labs