Thanks! On Wed, Sep 09, 2020 at 06:19:06AM -0700, syzbot wrote: > syzbot has bisected this issue to: > > commit f08e3888574d490b31481eef6d84c61bedba7a47 > Author: Boqun Feng <boqun.feng@xxxxxxxxx> > Date: Fri Aug 7 07:42:30 2020 +0000 > > lockdep: Fix recursive read lock related safe->unsafe detection > > bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=13034be1900000 > start commit: dff9f829 Add linux-next specific files for 20200908 > git tree: linux-next > final oops: https://syzkaller.appspot.com/x/report.txt?x=10834be1900000 > console output: https://syzkaller.appspot.com/x/log.txt?x=17034be1900000 > kernel config: https://syzkaller.appspot.com/x/.config?x=37b3426c77bda44c > dashboard link: https://syzkaller.appspot.com/bug?extid=22e87cdf94021b984aa6 > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=108b740d900000 > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=12daa9ed900000 > > Reported-by: syzbot+22e87cdf94021b984aa6@xxxxxxxxxxxxxxxxxxxxxxxxx > Fixes: f08e3888574d ("lockdep: Fix recursive read lock related safe->unsafe detection") > This is another deadlock possibility detected by lockdep's new detection algorithm. The deadlock happens as follow: CPU 0 CPU 1 CPU 2 read_lock(&fown->lock); spin_lock_irqsave(&dev->event_lock, ...) write_lock_irq(&filp->f_owner.lock); // wait for the lock read_lock(&fown-lock); // have to wait until the writer release // due to the fairness <interrupted> spin_lock_irqsave(&dev->event_lock); // wait for the lock The lock dependency on CPU 1 happens if there exists a call sequence: input_inject_event(): spin_lock_irqsave(&dev->event_lock,...); input_handle_event(): input_pass_values(): input_to_handler(): handler->event(): // evdev_event() evdev_pass_values(): spin_lock(&client->buffer_lock); __pass_event(): kill_fasync(): kill_fasync_rcu(): read_lock(&fa->fa_lock); send_sigio(): read_lock(&fown->lock); A possible fix would be replacing the read_lock() with read_lock_irq() or read_lock_irqsave(). Regards, Boqun > For information about bisection process see: https://goo.gl/tpsmEJ#bisection
