Re: [PATCH] Input: mousedev - add a schedule point in mousedev_write()
From: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Date: 2018-10-04 18:59:56
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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...
quoted hunk ↗ jump to hunk
Link: https://lkml.org/lkml/2018/8/23/1106 Signed-off-by: Eric Dumazet <edumazet@google.com> Reported-by: syzbot+9436b02171ac0894d33e@syzkaller.appspotmail.com Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com> 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