Re: [PATCH] nbd: Fix hung when signal interrupts nbd_start_device_ioctl()

[Josef Bacik <josef@toxicpanda.com>]

On Thu, Sep 08, 2022 at 01:35:02AM +0900, Shigeru Yoshida wrote:
> syzbot reported hung task [1].  The following program is a simplified
> version of the reproducer:
> 
> int main(void)
> {
> 	int sv[2], fd;
> 
> 	if (socketpair(AF_UNIX, SOCK_STREAM, 0, sv) < 0)
> 		return 1;
> 	if ((fd = open("/dev/nbd0", 0)) < 0)
> 		return 1;
> 	if (ioctl(fd, NBD_SET_SIZE_BLOCKS, 0x81) < 0)
> 		return 1;
> 	if (ioctl(fd, NBD_SET_SOCK, sv[0]) < 0)
> 		return 1;
> 	if (ioctl(fd, NBD_DO_IT) < 0)
> 		return 1;
> 	return 0;
> }
> 
> When signal interrupt nbd_start_device_ioctl() waiting the condition
> atomic_read(&config->recv_threads) == 0, the task can hung because it
> waits the completion of the inflight IOs.
> 
> This patch fixes the issue by clearing queue, not just shutdown, when
> signal interrupt nbd_start_device_ioctl().
> 
> Link: https://syzkaller.appspot.com/bug?id=7d89a3ffacd2b83fdd39549bc4d8e0a89ef21239 [1]
> Reported-by: syzbot+38e6c55d4969a14c1534@syzkaller.appspotmail.com
> Signed-off-by: Shigeru Yoshida <syoshida@redhat.com>

Reviewed-by: Josef Bacik <josef@toxicpanda.com>

Thanks,

Josef