Re: possible deadlock in __do_page_fault

From: Dmitry Vyukov <dvyukov@google.com>
To: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: "Andrew Morton" <akpm@linux-foundation.org>,
	"Joel Fernandes" <joel@joelfernandes.org>,
	"Todd Kjos" <tkjos@google.com>,
	"Joel Fernandes" <joelaf@google.com>,
	syzbot+a76129f18c89f3e2ddd4@syzkaller.appspotmail.com,
	"Andi Kleen" <ak@linux.intel.com>,
	"Johannes Weiner" <hannes@cmpxchg.org>, "Jan Kara" <jack@suse.cz>,
	"Souptick Joarder" <jrdr.linux@gmail.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Linux-MM <linux-mm@kvack.org>,
	"Mel Gorman" <mgorman@techsingularity.net>,
	syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
	"Arve Hjønnevåg" <arve@android.com>,
	"Todd Kjos" <tkjos@android.com>,
	"Martijn Coenen" <maco@android.com>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>
Subject: Re: possible deadlock in __do_page_fault
Date: Tue, 22 Jan 2019 14:54:28 +0100	[thread overview]
Message-ID: <CACT4Y+b7KhMECUF01fz0+1LJOiqzJhTRHOvezN4baPNd02om0Q@mail.gmail.com> (raw)
In-Reply-To: <CACT4Y+YA38BfnByA_jrocbhbbqg7NWRe4-5UAp5Q-iKFi9hGQA@mail.gmail.com>

On Tue, Jan 22, 2019 at 2:52 PM Dmitry Vyukov <dvyukov@google.com> wrote:
>
> On Tue, Jan 22, 2019 at 11:32 AM Tetsuo Handa
> <penguin-kernel@i-love.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@i-love.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@joelfernandes.org> wrote:
> > >>>
> > >>>> On Thu, Sep 20, 2018 at 5:12 PM Todd Kjos <tkjos@google.com> wrote:
> > >>>>>
> > >>>>> +Joel Fernandes
> > >>>>>
> > >>>>> On Thu, Sep 20, 2018 at 2:11 PM Andrew Morton <akpm@linux-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

This of course should be:

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