linux-kernel - Re: KASAN: null-ptr-deref Read in reclaim

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Message-Id: <20190311232541.db8571d2e3e0ca636785f31f@linux-foundation.org>
Date:   Mon, 11 Mar 2019 23:25:41 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     syzbot <syzbot+fa11f9da42b46cea3b4a@...kaller.appspotmail.com>,
        cgroups@...r.kernel.org, Johannes Weiner <hannes@...xchg.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>, Michal Hocko <mhocko@...nel.org>,
        Michal Hocko <mhocko@...e.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Shakeel Butt <shakeelb@...gle.com>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Vladimir Davydov <vdavydov.dev@...il.com>
Subject: Re: KASAN: null-ptr-deref Read in reclaim_high

On Tue, 12 Mar 2019 07:08:38 +0100 Dmitry Vyukov <dvyukov@...gle.com> wrote:

> On Tue, Mar 12, 2019 at 12:37 AM Andrew Morton
> <akpm@...ux-foundation.org> wrote:
> >
> > On Mon, 11 Mar 2019 06:08:01 -0700 syzbot <syzbot+fa11f9da42b46cea3b4a@...kaller.appspotmail.com> wrote:
> >
> > > syzbot has bisected this bug to:
> > >
> > > commit 29a4b8e275d1f10c51c7891362877ef6cffae9e7
> > > Author: Shakeel Butt <shakeelb@...gle.com>
> > > Date:   Wed Jan 9 22:02:21 2019 +0000
> > >
> > >      memcg: schedule high reclaim for remote memcgs on high_work
> > >
> > > bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=155bf5db200000
> > > start commit:   29a4b8e2 memcg: schedule high reclaim for remote memcgs on..
> > > git tree:       linux-next
> > > final crash:    https://syzkaller.appspot.com/x/report.txt?x=175bf5db200000
> > > console output: https://syzkaller.appspot.com/x/log.txt?x=135bf5db200000
> > > kernel config:  https://syzkaller.appspot.com/x/.config?x=611f89e5b6868db
> > > dashboard link: https://syzkaller.appspot.com/bug?extid=fa11f9da42b46cea3b4a
> > > userspace arch: amd64
> > > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14259017400000
> > > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=141630a0c00000
> > >
> > > Reported-by: syzbot+fa11f9da42b46cea3b4a@...kaller.appspotmail.com
> > > Fixes: 29a4b8e2 ("memcg: schedule high reclaim for remote memcgs on
> > > high_work")
> >
> > The following patch
> > memcg-schedule-high-reclaim-for-remote-memcgs-on-high_work-v3.patch
> > might have fixed this.  Was it applied?
> 
> Hi Andrew,
> 
> You mean if the patch was applied during the bisection?
> No, it wasn't. Bisection is very specifically done on the same tree
> where the bug was hit. There are already too many factors that make
> the result flaky/wrong/inconclusive without changing the tree state.
> Now, if syzbot would know about any pending fix for this bug, then it
> would not do the bisection at all. But it have not seen any patch in
> upstream/linux-next with the Reported-by tag, nor it received any syz
> fix commands for this bugs. Should have been it aware of the fix? How?

memcg-schedule-high-reclaim-for-remote-memcgs-on-high_work-v3.patch was
added to linux-next on Jan 10.  I take it that this bug was hit when
testing the entire linux-next tree, so we can assume that
memcg-schedule-high-reclaim-for-remote-memcgs-on-high_work-v3.patch
does not fix it, correct?

In which case, over to Shakeel!