From: Dmitry Vyukov <dvyukov@google.com>
To: Waiman Long <longman@redhat.com>
Cc: syzbot <syzbot+a9fb1457d720a55d6dc5@syzkaller.appspotmail.com>,
Alexey Dobriyan <adobriyan@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
allison@lohutok.net, areber@redhat.com,
aubrey.li@linux.intel.com, Andrei Vagin <avagin@gmail.com>,
Bruce Fields <bfields@fieldses.org>,
Christian Brauner <christian@brauner.io>,
cyphar@cyphar.com, "Eric W. Biederman" <ebiederm@xmission.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
guro@fb.com, Jeff Layton <jlayton@kernel.org>,
Joel Fernandes <joel@joelfernandes.org>,
Kees Cook <keescook@chromium.org>,
linmiaohe@huawei.com,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Michal Hocko <mhocko@suse.com>, Ingo Molnar <mingo@kernel.org>,
Oleg Nesterov <oleg@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
sargun@sargun.me,
syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
Thomas Gleixner <tglx@linutronix.de>,
Al Viro <viro@zeniv.linux.org.uk>
Subject: Re: possible deadlock in send_sigio
Date: Thu, 11 Jun 2020 09:43:58 +0200 [thread overview]
Message-ID: <CACT4Y+brpePBoR7EUwPiSvGAgo6bhvpKvLTiCaCfRSadzn6yRw@mail.gmail.com> (raw)
In-Reply-To: <69818a6c-7025-8950-da4b-7fdc065d90d6@redhat.com>
On Thu, Jun 11, 2020 at 4:33 AM Waiman Long <longman@redhat.com> wrote:
>
> On 4/4/20 1:55 AM, syzbot wrote:
> > Hello,
> >
> > syzbot found the following crash on:
> >
> > HEAD commit: bef7b2a7 Merge tag 'devicetree-for-5.7' of git://git.kerne..
> > git tree: upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=15f39c5de00000
> > kernel config: https://syzkaller.appspot.com/x/.config?x=91b674b8f0368e69
> > dashboard link: https://syzkaller.appspot.com/bug?extid=a9fb1457d720a55d6dc5
> > compiler: gcc (GCC) 9.0.0 20181231 (experimental)
> > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1454c3b7e00000
> > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=12a22ac7e00000
> >
> > The bug was bisected to:
> >
> > commit 7bc3e6e55acf065500a24621f3b313e7e5998acf
> > Author: Eric W. Biederman <ebiederm@xmission.com>
> > Date: Thu Feb 20 00:22:26 2020 +0000
> >
> > proc: Use a list of inodes to flush from proc
> >
> > bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=165c4acde00000
> > final crash: https://syzkaller.appspot.com/x/report.txt?x=155c4acde00000
> > console output: https://syzkaller.appspot.com/x/log.txt?x=115c4acde00000
> >
> > IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > Reported-by: syzbot+a9fb1457d720a55d6dc5@syzkaller.appspotmail.com
> > Fixes: 7bc3e6e55acf ("proc: Use a list of inodes to flush from proc")
> >
> > ========================================================
> > WARNING: possible irq lock inversion dependency detected
> > 5.6.0-syzkaller #0 Not tainted
> > --------------------------------------------------------
> > ksoftirqd/0/9 just changed the state of lock:
> > ffffffff898090d8 (tasklist_lock){.+.?}-{2:2}, at: send_sigio+0xa9/0x340 fs/fcntl.c:800
> > but this lock took another, SOFTIRQ-unsafe lock in the past:
> > (&pid->wait_pidfd){+.+.}-{2:2}
> >
> >
> > and interrupts could create inverse lock ordering between them.
> >
> >
> > other info that might help us debug this:
> > Possible interrupt unsafe locking scenario:
> >
> > CPU0 CPU1
> > ---- ----
> > lock(&pid->wait_pidfd);
> > local_irq_disable();
> > lock(tasklist_lock);
> > lock(&pid->wait_pidfd);
> > <Interrupt>
> > lock(tasklist_lock);
> >
> > *** DEADLOCK ***
>
> That is a false positive. The qrwlock has the special property that it
> becomes unfair (for read lock) at interrupt context. So unless it is
> taking a write lock in the interrupt context, it won't go into deadlock.
> The current lockdep code does not capture the full semantics of qrwlock
> leading to this false positive.
Hi Longman
Thanks for looking into this.
Now the question is: how should we change lockdep annotations to fix this bug?
next prev parent reply other threads:[~2020-06-11 7:44 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-04 5:55 possible deadlock in send_sigio syzbot
2020-06-11 2:32 ` Waiman Long
2020-06-11 7:43 ` Dmitry Vyukov [this message]
2020-06-11 13:51 ` Waiman Long
2020-06-11 14:22 ` Peter Zijlstra
2020-06-11 16:09 ` Waiman Long
2020-06-11 23:55 ` Boqun Feng
2020-06-12 1:55 ` Waiman Long
2020-06-12 7:01 ` Boqun Feng
2020-06-15 16:37 ` Waiman Long
2020-06-15 16:49 ` Matthew Wilcox
2020-06-15 17:13 ` Waiman Long
2020-06-15 20:40 ` Matthew Wilcox
2020-06-16 0:13 ` Boqun Feng
2020-06-16 0:31 ` Waiman Long
2020-06-11 16:07 ` Eric W. Biederman
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