Hi Eric, On Thu, Oct 04, 2018 at 08:47:49AM -0700, Eric Dumazet wrote: > syzbot was able to trigger rcu stalls by calling write() > with large number of bytes. > > Add a cond_resched() in the loop to avoid this.
I think this simply masks a deeper issue. The code fetches characters from userspace in a loop, takes a lock, quickly places response in an output buffer, and releases interrupt. I do not see why this should cause stalls as we do not hold spinlock/interrupts off for extended period of time. Adding Paul so he can straighten me out... > > Link: https://lkml.org/lkml/2018/8/23/1106 > Signed-off-by: Eric Dumazet <eduma...@google.com> > Reported-by: syzbot+9436b02171ac0894d...@syzkaller.appspotmail.com > Cc: Dmitry Torokhov <dmitry.torok...@gmail.com> > Cc: linux-in...@vger.kernel.org > --- > drivers/input/mousedev.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/drivers/input/mousedev.c b/drivers/input/mousedev.c > index > e08228061bcdd2f97aaadece31d6c83eb7539ae5..412fa71245afe26a7a8ad75705566f83633ba347 > 100644 > --- a/drivers/input/mousedev.c > +++ b/drivers/input/mousedev.c > @@ -707,6 +707,7 @@ static ssize_t mousedev_write(struct file *file, const > char __user *buffer, > mousedev_generate_response(client, c); > > spin_unlock_irq(&client->packet_lock); > + cond_resched(); > } > > kill_fasync(&client->fasync, SIGIO, POLL_IN); > -- > 2.19.0.605.g01d371f741-goog > Thanks. -- Dmitry
