Re: [Qemu-devel] [PATCH] Revert "qed: Implement .bdrv_drain"

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Tue, Mar 08, 2016 at 10:11:16AM +0000, Stefan Hajnoczi wrote:
> This reverts commit df9a681dc9ad41c9cdeb9ecc5d060ba9abd27e01.
> 
> Note that commit df9a681dc9ad41c9cdeb9ecc5d060ba9abd27e01 included some
> unrelated hunks, possibly due to a merge failure or an overlooked
> squash.  This only reverts the qed .bdrv_drain() implementation.
> 
> The qed .bdrv_drain() implementation is unsafe and can lead to a double
> request completion.
> 
> Paolo Bonzini reports:
> "The problem is that bdrv_qed_drain calls qed_plug_allocating_write_reqs
> unconditionally, but this is not correct if an allocating write is
> queued.  In this case, qed_unplug_allocating_write_reqs will restart the
> allocating write and possibly cause it to complete.  The aiocb however
> is still in use for the L2/L1 table writes, and will then be completed
> again as soon as the table writes are stable."
> 
> For QEMU 2.6 we can simply revert this commit.  A full solution for the
> qed need check timer may be added if the bdrv_drain() implementation is
> extended.
> 
> Reported-by: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  block/qed.c | 13 -------------
>  1 file changed, 13 deletions(-)
> 
> Passes ./check -qed.

Thanks, applied to my block tree:
https://github.com/stefanha/qemu/commits/block

Stefan

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