linux-kernel - Re: [syzbot] WARNING: suspicious RCU usage in get

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Date:   Fri, 7 May 2021 10:37:56 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     syzbot <syzbot+37fc8b84ffa2279d636d@...kaller.appspotmail.com>
Cc:     axboe@...nel.dk, christian@...uner.io, ebiederm@...ssion.com,
        linux-kernel@...r.kernel.org, oleg@...hat.com, pcc@...gle.com,
        syzkaller-bugs@...glegroups.com, tglx@...utronix.de,
        Paul McKenney <paulmck@...nel.org>
Subject: Re: [syzbot] WARNING: suspicious RCU usage in get_signal

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@...kaller.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.