2022-09-07 16:44:37

by Shigeru Yoshida

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

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: [email protected]
Signed-off-by: Shigeru Yoshida <[email protected]>
---
drivers/block/nbd.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index 2a709daefbc4..2a2a1d996a57 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -1413,10 +1413,12 @@ static int nbd_start_device_ioctl(struct nbd_device *nbd)
mutex_unlock(&nbd->config_lock);
ret = wait_event_interruptible(config->recv_wq,
atomic_read(&config->recv_threads) == 0);
- if (ret)
+ if (ret) {
sock_shutdown(nbd);
- flush_workqueue(nbd->recv_workq);
+ nbd_clear_que(nbd);
+ }

+ flush_workqueue(nbd->recv_workq);
mutex_lock(&nbd->config_lock);
nbd_bdev_reset(nbd);
/* user requested, ignore socket errors */
--
2.37.3

2022-09-07 18:25:46

by Josef Bacik

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

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: [email protected]
> Signed-off-by: Shigeru Yoshida <[email protected]>

Reviewed-by: Josef Bacik <[email protected]>

Thanks,

Josef

2022-09-08 15:00:42

by Jens Axboe

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

On Thu, 8 Sep 2022 01:35:02 +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;
>
> [...]

Applied, thanks!

[1/1] nbd: Fix hung when signal interrupts nbd_start_device_ioctl()
commit: 1de7c3cf48fc41cd95adb12bd1ea9033a917798a

Best regards,
--
Jens Axboe