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    Subject[PATCH 5.15 484/530] nbd: Fix hung when signal interrupts nbd_start_device_ioctl()
    Date
    From: Shigeru Yoshida <syoshida@redhat.com>

    [ Upstream commit 1de7c3cf48fc41cd95adb12bd1ea9033a917798a ]

    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>
    Link: https://lore.kernel.org/r/20220907163502.577561-1-syoshida@redhat.com
    Signed-off-by: Jens Axboe <axboe@kernel.dk>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    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 b391ca062add..ec2b5dd2ce4a 100644
    --- a/drivers/block/nbd.c
    +++ b/drivers/block/nbd.c
    @@ -1351,10 +1351,12 @@ static int nbd_start_device_ioctl(struct nbd_device *nbd, struct block_device *b
    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(bdev);
    /* user requested, ignore socket errors */
    --
    2.35.1


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