All of lore.kernel.org
 help / color / mirror / Atom feed
From: Dmitry Vyukov <dvyukov@google.com>
To: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
	syzbot <syzbot+37fc8b84ffa2279d636d@syzkaller.appspotmail.com>,
	Jens Axboe <axboe@kernel.dk>,
	Christian Brauner <christian@brauner.io>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Oleg Nesterov <oleg@redhat.com>,
	Peter Collingbourne <pcc@google.com>,
	syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
	Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [syzbot] WARNING: suspicious RCU usage in get_signal
Date: Sat, 8 May 2021 07:03:51 +0200	[thread overview]
Message-ID: <CACT4Y+Ydu6Dcmx1tXe-1aOw-hAcHgjwncrSmWuEr_8tfq02Dtg@mail.gmail.com> (raw)
In-Reply-To: <20210507171901.GV975577@paulmck-ThinkPad-P17-Gen-1>

On Fri, May 7, 2021 at 7:19 PM Paul E. McKenney <paulmck@kernel.org> wrote:
>
> On Fri, May 07, 2021 at 10:42:48AM +0200, Dmitry Vyukov wrote:
> > On Fri, May 7, 2021 at 10:38 AM Peter Zijlstra <peterz@infradead.org> wrote:
> > >
> > > On Thu, May 06, 2021 at 02:34:27PM -0700, syzbot wrote:
> > > > Hello,
> > > >
> > > > syzbot found the following issue on:
> > > >
> > > > HEAD commit:    d2b6f8a1 Merge tag 'xfs-5.13-merge-3' of git://git.kernel...
> > > > git tree:       upstream
> > > > console output: https://syzkaller.appspot.com/x/log.txt?x=123a56a5d00000
> > > > kernel config:  https://syzkaller.appspot.com/x/.config?x=65c207250bba4efe
> > > > dashboard link: https://syzkaller.appspot.com/bug?extid=37fc8b84ffa2279d636d
> > > > userspace arch: i386
> > > >
> > > > Unfortunately, I don't have any reproducer for this issue yet.
> > > >
> > > > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > > > Reported-by: syzbot+37fc8b84ffa2279d636d@syzkaller.appspotmail.com
> > > >
> > > > =============================
> > > > WARNING: suspicious RCU usage
> > > > 5.12.0-syzkaller #0 Not tainted
> > > > -----------------------------
> > > > kernel/sched/core.c:8304 Illegal context switch in RCU-sched read-side critical section!
> > > >
> > > > other info that might help us debug this:
> > > >
> > > >
> > > > rcu_scheduler_active = 2, debug_locks = 0
> > > > no locks held by syz-executor.4/10430.
> > >
> > > Looks like this is a concurrent fail?, if !debug_locks (as per the above)
> > > then RCU_LOCKDEP_WARN() should not trigger.
> >
> > FTR the log is here:
> > https://syzkaller.appspot.com/text?tag=CrashLog&x=123a56a5d00000
> >
> > It contains 2 intermixed reports:
> >
> > [  289.896033][T10430] =============================
> > [  289.896039][T10430] WARNING: suspicious RCU usage
> > [  289.896046][T10430] 5.12.0-syzkaller #0 Not tainted
> > [  289.898388][T13493] ======================================================
> > [  289.898401][T13493] WARNING: possible circular locking dependency detected
> > [  289.898410][T13493] 5.12.0-syzkaller #0 Not tainted
> > [  289.898424][T13493] ------------------------------------------------------
> > [  289.898432][T13493] syz-executor.0/13493 is trying to acquire lock:
> > [  289.898448][T13493] ffff888019065ca0 (&bdev->bd_mutex){+.+.}-{3:3},
> > at: del_gendisk+0x250/0x9e0
>
> This "suspicious RCU usage" false positive looks to be addressed by this
> commit in -rcu, slated for the v5.14 merge window:
>
> 81a5e05455d4 ("rcu: Reject RCU_LOCKDEP_WARN() false positives")
>
> So I suggest ignoring the "suspicious RCU usage" report in favor of the
> "possible circular locking dependency detected" report.

Oh, I see, it's not merged yet.
In my memory we discussed it so long ago that I assumed it is fixed already.
Let's mark it as fixed then:

#syz fix: rcu: Reject RCU_LOCKDEP_WARN() false positives

Thanks for double checking.

  reply	other threads:[~2021-05-08  5:04 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-06 21:34 [syzbot] WARNING: suspicious RCU usage in get_signal syzbot
2021-05-07  8:37 ` Peter Zijlstra
2021-05-07  8:42   ` Dmitry Vyukov
2021-05-07 17:19     ` Paul E. McKenney
2021-05-08  5:03       ` Dmitry Vyukov [this message]
2021-05-08 22:59         ` Paul E. McKenney

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=CACT4Y+Ydu6Dcmx1tXe-1aOw-hAcHgjwncrSmWuEr_8tfq02Dtg@mail.gmail.com \
    --to=dvyukov@google.com \
    --cc=axboe@kernel.dk \
    --cc=christian@brauner.io \
    --cc=ebiederm@xmission.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=oleg@redhat.com \
    --cc=paulmck@kernel.org \
    --cc=pcc@google.com \
    --cc=peterz@infradead.org \
    --cc=syzbot+37fc8b84ffa2279d636d@syzkaller.appspotmail.com \
    --cc=syzkaller-bugs@googlegroups.com \
    --cc=tglx@linutronix.de \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.