Re: [Qemu-devel] Hibernate and qemu-nbd

[Stefan Hajnoczi <stefanha@gmail.com>]

On Tue, Sep 17, 2013 at 07:10:44AM -0700, Mark Trumpold wrote:
> I am using the kernel functionality directly with the commands:
>     echo platform >/sys/power/disk
>     echo disk >/sys/power/state
> 
> The following appears in dmesg when I attempt to hibernate:
> 
> ====================================================
> [   38.881397] nbd (pid 1473: qemu-nbd) got signal 0
> [   38.881401] block nbd0: shutting down socket
> [   38.881404] block nbd0: Receive control failed (result -4)
> [   38.881417] block nbd0: queue cleared
> [   87.463133] block nbd0: Attempted send on closed socket
> [   87.463137] end_request: I/O error, dev nbd0, sector 66824
> ====================================================
> 
> My environment:
>   Debian: 6.0.5
>   Kernel: 3.3.1
>   Qemu userspace: 1.2.0

This could be a bug in the nbd client kernel module.
drivers/block/nbd.c:sock_xmit() does the following:

            result = kernel_recvmsg(sock, &msg, &iov, 1, size,
                                    msg.msg_flags);

    if (signal_pending(current)) {
            siginfo_t info;
            printk(KERN_WARNING "nbd (pid %d: %s) got signal %d\n",
                    task_pid_nr(current), current->comm,
                    dequeue_signal_lock(current, &current->blocked, &info));
            result = -EINTR;
            sock_shutdown(nbd, !send);
            break;
    }

The signal number in the log output looks bogus, we shouldn't get 0.
sock_xmit() actually blocks all signals except SIGKILL before calling
kernel_recvmsg().  I guess this is an artifact of the suspend-to-disk
operation, maybe the signal pending flag is set on the process.

Perhaps someone with a better understanding of the kernel internals can
check this?

What happens next is that the nbd kernel module shuts down the NBD connection.

As a workaround, please try running a separate nbd-client(1) process and drop
the qemu-nbd -c command-line argument.  This way nbd-client(1) uses the
nbd kernel module instead of the qemu-nbd process and you'll get the
benefit of nbd-client's automatic reconnect.

Stefan