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SubjectRe: [PATCH 1/1] NBD: fix I/O hang on disconnected nbds
On Mon, 09 Feb 2009 13:21:51 -0500
Paul Clements <paul.clements@steeleye.com> wrote:

> This patch fixes a problem that causes I/O to a disconnected
> (or partially initialized) nbd device to hang indefinitely. To reproduce:
>
> # ioctl NBD_SET_SIZE_BLOCKS /dev/nbd23 514048
> # dd if=/dev/nbd23 of=/dev/null bs=4096 count=1
>
> ...hangs...
>
> This can also occur when an nbd device loses its nbd-client/server
> connection. Although we clear the queue of any outstanding I/Os after
> the client/server connection fails, any additional I/Os that get queued
> later will hang.
>
> This bug may also be the problem reported in this bug report:
> http://bugzilla.kernel.org/show_bug.cgi?id=12277
>
> Testing would need to be performed to determine if the two issues are
> the same.
>
> This problem was introduced by the new request handling thread code
> ("NBD: allow nbd to be used locally", 3/2008), which entered into
> mainline around 2.6.25.

Seems that the patch applies to 2.6.26, but not to 2.6.25.

>
> The fix, which is fairly simple, is to restore the check for lo->sock
> being NULL in do_nbd_request. This causes I/O to an uninitialized nbd to
> immediately fail with an I/O error, as it did prior to the introduction
> of this bug.

I marked this as needing backporting into 2.6.26.x, 2.6.27.x and
2.6.28.x. OK?



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