From: "Theodore Y. Ts'o" <tytso@mit.edu>
To: Dmitry Vyukov <dvyukov@google.com>
Cc: syzbot <syzbot+7d19c5fe6a3f1161abb7@syzkaller.appspotmail.com>,
Andreas Dilger <adilger.kernel@dilger.ca>,
<linux-ext4@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Arnaldo Carvalho de Melo <acme@kernel.org>
Subject: Re: INFO: rcu detected stall in ext4_file_write_iter
Date: Wed, 27 Feb 2019 16:57:55 -0500 [thread overview]
Message-ID: <20190227215755.GD10828@mit.edu> (raw)
In-Reply-To: <CACT4Y+acnJnZ4rN3Ta-6ftFv4A=1q7hsVQSVJeh9PGCK0e4BbA@mail.gmail.com>
On Wed, Feb 27, 2019 at 10:58:50AM +0100, Dmitry Vyukov wrote:
> Peter, Ingo, do you have any updates on the
> perf_event_open/sched_setattr stalls? This bug cause assorted hangs
> throughout kernel and so is nasty.
>
> syzkaller tries to remove all syscalls from reproducers one-by-one.
> Somehow without sched_setattr the hang did not reproduce (a bunch of
> repros have perf_event_open+sched_setattr so somehow they seem to be
> related)
FWIW, at least for me, the repro.c with sched_setattr commented out
(see the repro.c attached to a message[1] earlier in the thread) it
was reproducing reliably on a 2 CPU, 2 GB memory KVM using the
ext4.git tree (dev branch, 5.0-rc3 plus ext4 commits for the next
merge window) using a Debian stable-based VM[2].
[1] https://groups.google.com/d/msg/syzkaller-bugs/ByPpM3WZw1s/li7SsaEyAgAJ
[2] https://mirrors.edge.kernel.org/pub/linux/kernel/people/tytso/kvm-xfstests/root_fs.img.amd64
> But even with perfect repros machines still won't be
> able to tell in all cases that even though the hang happened in ext4
> code, the root cause is actually another scheduler-related system
> call. So thanks for looking into this.
To be clear, there was *not* a scheduler-related system call in the
repro.c I was playing with (see [2]); just perf_event_open(2) and
sendfile(2).
Cheers,
- Ted
next prev parent reply other threads:[~2019-02-27 21:58 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <0000000000009a01370582c6772a@google.com>
2019-02-26 15:17 ` INFO: rcu detected stall in ext4_file_write_iter Theodore Y. Ts'o
2019-02-27 9:58 ` Dmitry Vyukov
2019-02-27 21:57 ` Theodore Y. Ts'o [this message]
2019-02-28 9:34 ` Dmitry Vyukov
2019-03-21 17:30 ` syzbot
2020-09-11 19:33 ` syzbot
2020-09-11 20:03 ` Jens Axboe
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