From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dmitry Torokhov Subject: Re: [PATCH] Input: mousedev - add a schedule point in mousedev_write() Date: Thu, 4 Oct 2018 11:59:49 -0700 Message-ID: <20181004185949.GA233675@dtor-ws> References: <20181004154749.111595-1-edumazet@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20181004154749.111595-1-edumazet@google.com> Sender: linux-kernel-owner@vger.kernel.org To: Eric Dumazet Cc: linux-kernel , Eric Dumazet , linux-input@vger.kernel.org, "Paul E. McKenney" List-Id: linux-input@vger.kernel.org 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 > Reported-by: syzbot+9436b02171ac0894d33e@syzkaller.appspotmail.com > Cc: Dmitry Torokhov > Cc: linux-input@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