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SubjectRe: KASAN: null-ptr-deref Read in reclaim_high
On Tue, 12 Mar 2019 07:08:38 +0100 Dmitry Vyukov <dvyukov@google.com> wrote:

> On Tue, Mar 12, 2019 at 12:37 AM Andrew Morton
> <akpm@linux-foundation.org> wrote:
> >
> > On Mon, 11 Mar 2019 06:08:01 -0700 syzbot <syzbot+fa11f9da42b46cea3b4a@syzkaller.appspotmail.com> wrote:
> >
> > > syzbot has bisected this bug to:
> > >
> > > commit 29a4b8e275d1f10c51c7891362877ef6cffae9e7
> > > Author: Shakeel Butt <shakeelb@google.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@syzkaller.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!

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