From: Christian Brauner <christian.brauner@ubuntu.com>
To: Andrea Parri <parri.andrea@gmail.com>
Cc: bsingharora@gmail.com, elver@google.com,
linux-kernel@vger.kernel.org,
syzbot+c5d03165a1bd1dead0c1@syzkaller.appspotmail.com,
syzkaller-bugs@googlegroups.com,
Dmitry Vyukov <dvyukov@google.com>
Subject: Re: [PATCH] taskstats: fix data-race
Date: Mon, 7 Oct 2019 12:50:45 +0200 [thread overview]
Message-ID: <20191007105044.x7srxpcedfo3o5m4@wittgenstein> (raw)
In-Reply-To: <20191007104039.GA16085@andrea.guest.corp.microsoft.com>
On Mon, Oct 07, 2019 at 12:40:39PM +0200, Andrea Parri wrote:
> Hi Christian,
>
> On Mon, Oct 07, 2019 at 01:52:16AM +0200, Christian Brauner wrote:
> > When assiging and testing taskstats in taskstats_exit() there's a race
> > when writing and reading sig->stats when a thread-group with more than
> > one thread exits:
> >
> > cpu0:
> > thread catches fatal signal and whole thread-group gets taken down
> > do_exit()
> > do_group_exit()
> > taskstats_exit()
> > taskstats_tgid_alloc()
> > The tasks reads sig->stats holding sighand lock seeing garbage.
> >
> > cpu1:
> > task calls exit_group()
> > do_exit()
> > do_group_exit()
> > taskstats_exit()
> > taskstats_tgid_alloc()
> > The task takes sighand lock and assigns new stats to sig->stats.
> >
> > Fix this by using READ_ONCE() and smp_store_release().
> >
> > Reported-by: syzbot+c5d03165a1bd1dead0c1@syzkaller.appspotmail.com
> > Cc: Dmitry Vyukov <dvyukov@google.com>
> > Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
>
> FYI, checkpatch.pl says:
>
> WARNING: memory barrier without comment
> #62: FILE: kernel/taskstats.c:568:
> + smp_store_release(&sig->stats, stats_new);
>
> Maybe you can make checkpatch.pl happy ;-) and add a comment to stress
> the 'pairing' between this barrier and the added READ_ONCE() (as Dmitry
> was alluding to in a previous post)?
Of course. I totally forgot the memory barrier documentation requirement.
Christian
next prev parent reply other threads:[~2019-10-07 10:50 UTC|newest]
Thread overview: 62+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-05 4:26 KCSAN: data-race in taskstats_exit / taskstats_exit syzbot
2019-10-05 4:29 ` Dmitry Vyukov
2019-10-05 11:29 ` Christian Brauner
2019-10-05 11:28 ` [PATCH] taskstats: fix data-race Christian Brauner
2019-10-05 13:33 ` Marco Elver
2019-10-05 14:15 ` Christian Brauner
2019-10-05 14:34 ` Marco Elver
2019-10-06 10:00 ` Dmitry Vyukov
2019-10-06 10:59 ` Christian Brauner
2019-10-06 23:52 ` Christian Brauner
2019-10-07 7:31 ` Dmitry Vyukov
2019-10-07 9:29 ` Christian Brauner
2019-10-07 10:40 ` Andrea Parri
2019-10-07 10:50 ` Christian Brauner [this message]
2019-10-07 11:01 ` [PATCH v2] " Christian Brauner
2019-10-07 13:18 ` Andrea Parri
2019-10-07 13:28 ` Christian Brauner
2019-10-07 13:50 ` Dmitry Vyukov
2019-10-07 13:55 ` Christian Brauner
2019-10-07 14:08 ` Dmitry Vyukov
2019-10-07 14:10 ` Christian Brauner
2019-10-07 14:14 ` Andrea Parri
2019-10-07 14:18 ` Dmitry Vyukov
2019-10-08 14:20 ` Andrea Parri
2019-10-08 14:24 ` Christian Brauner
2019-10-08 15:26 ` Andrea Parri
2019-10-08 15:35 ` Christian Brauner
2019-10-08 15:44 ` Andrea Parri
2019-10-09 11:31 ` [PATCH] " Christian Brauner
2019-10-09 11:40 ` Christian Brauner
2019-10-09 11:48 ` [PATCH v5] " Christian Brauner
2019-10-09 12:08 ` Andrea Parri
2019-10-09 13:26 ` Christian Brauner
2019-10-21 11:33 ` [PATCH v6] " Christian Brauner
2019-10-21 12:19 ` Rasmus Villemoes
2019-10-21 13:04 ` Christian Brauner
2019-11-29 17:56 ` Will Deacon
2019-11-30 15:08 ` Christian Brauner
2019-10-23 12:16 ` Andrea Parri
2019-10-23 12:39 ` Dmitry Vyukov
2019-10-23 13:11 ` Christian Brauner
2019-10-23 13:20 ` Dmitry Vyukov
2019-10-24 11:31 ` Andrea Parri
2019-10-24 11:51 ` Dmitry Vyukov
2019-10-24 13:05 ` Andrea Parri
2019-10-24 13:13 ` Dmitry Vyukov
2019-10-24 13:21 ` Christian Brauner
2019-10-24 13:34 ` Dmitry Vyukov
2019-10-24 13:43 ` Andrea Parri
2019-10-24 13:58 ` Dmitry Vyukov
2019-10-24 14:40 ` Andrea Parri
2019-10-24 14:49 ` Dmitry Vyukov
2019-11-29 17:57 ` Will Deacon
2019-10-09 11:48 ` [PATCH] " Marco Elver
2019-10-09 11:53 ` Christian Brauner
2019-11-06 0:27 ` Balbir Singh
2019-11-06 0:09 ` KCSAN: data-race in taskstats_exit / taskstats_exit Balbir Singh
2019-11-06 10:23 ` Marco Elver
2019-11-07 10:39 ` Balbir Singh
2019-11-08 0:54 ` Balbir Singh
2019-11-08 8:55 ` Dmitry Vyukov
2019-11-09 3:42 ` Balbir Singh
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