linux-kernel - Re: possible deadlock in __do_page

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Date:   Tue, 22 Jan 2019 14:52:47 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Todd Kjos <tkjos@...gle.com>,
        Joel Fernandes <joelaf@...gle.com>,
        syzbot+a76129f18c89f3e2ddd4@...kaller.appspotmail.com,
        Andi Kleen <ak@...ux.intel.com>,
        Johannes Weiner <hannes@...xchg.org>, Jan Kara <jack@...e.cz>,
        Souptick Joarder <jrdr.linux@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        Matthew Wilcox <mawilcox@...rosoft.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Arve Hjønnevåg <arve@...roid.com>,
        Todd Kjos <tkjos@...roid.com>,
        Martijn Coenen <maco@...roid.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: possible deadlock in __do_page_fault

On Tue, Jan 22, 2019 at 11:32 AM Tetsuo Handa
<penguin-kernel@...ove.sakura.ne.jp> wrote:
>
> On 2019/01/22 19:12, Dmitry Vyukov wrote:
> > On Tue, Jan 22, 2019 at 11:02 AM Tetsuo Handa
> > <penguin-kernel@...ove.sakura.ne.jp> wrote:
> >>
> >> On 2018/09/22 8:21, Andrew Morton wrote:
> >>> On Thu, 20 Sep 2018 19:33:15 -0400 Joel Fernandes <joel@...lfernandes.org> wrote:
> >>>
> >>>> On Thu, Sep 20, 2018 at 5:12 PM Todd Kjos <tkjos@...gle.com> wrote:
> >>>>>
> >>>>> +Joel Fernandes
> >>>>>
> >>>>> On Thu, Sep 20, 2018 at 2:11 PM Andrew Morton <akpm@...ux-foundation.org> wrote:
> >>>>>>
> >>>>>>
> >>>>>> Thanks.  Let's cc the ashmem folks.
> >>>>>>
> >>>>
> >>>> This should be fixed by https://patchwork.kernel.org/patch/10572477/
> >>>>
> >>>> It has Neil Brown's Reviewed-by but looks like didn't yet appear in
> >>>> anyone's tree, could Greg take this patch?
> >>>
> >>> All is well.  That went into mainline yesterday, with a cc:stable.
> >>>
> >>
> >> This problem was not fixed at all.
> >
> > There are at least 2 other open deadlocks involving ashmem:
>
> Yes, they involve ashmem_shrink_scan() => {shmem|vfs}_fallocate() sequence.
> This approach tries to eliminate this sequence.
>
> >
> > https://syzkaller.appspot.com/bug?extid=148c2885d71194f18d28
> > https://syzkaller.appspot.com/bug?extid=4b8b031b89e6b96c4b2e
> >
> > Does this fix any of these too?
>
> I need checks from ashmem folks whether this approach is possible/correct.
> But you can ask syzbot to test this patch before ashmem folks respond.

Right. Let's do this.

As with any kernel changes only you really know how to apply it, git
tree/base commit info is missing, so let's do guessing and
finger-crossing as usual:

#syz fix: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
master

View attachment "ashmem.patch" of type "text/x-patch" (3279 bytes)