On Thu, Oct 4, 2018 at 11:59 AM Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx> wrote: > > 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... > Well... write(fd, buffer, 0x7FFF0000); Takes between 20 seconds and 2 minutes depending on CONFIG options .... So either apply my patch, or add a limit on the max count, and possibly break legitimate user space ? I dunno... > > > > Link: https://lkml.org/lkml/2018/8/23/1106 > > Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx> > > Reported-by: syzbot+9436b02171ac0894d33e@xxxxxxxxxxxxxxxxxxxxxxxxx > > Cc: Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx> > > Cc: linux-input@xxxxxxxxxxxxxxx > > --- > > 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
