Messages in this thread | | | Date | Fri, 7 May 2021 10:19:01 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [syzbot] WARNING: suspicious RCU usage in get_signal |
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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.
Thanx, Paul
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