Re: [PATCH 4/4] dma-helpers: don't lock AioContext in dma_blk_cb()

[Eric Blake]

On Thu, Nov 23, 2023 at 02:49:31PM -0500, Stefan Hajnoczi wrote:
> Commit abfcd2760b3e ("dma-helpers: prevent dma_blk_cb() vs
> dma_aio_cancel() race") acquired the AioContext lock inside dma_blk_cb()
> to avoid a race with scsi_device_purge_requests() running in the main
> loop thread.
> 
> The SCSI code no longer calls dma_aio_cancel() from the main loop thread
> while I/O is running in the IOThread AioContext. Therefore it is no
> longer necessary to take this lock to protect DMAAIOCB fields. The
> ->cb() function also does not require the lock because blk_aio_*() and
> friends do not need the AioContext lock.
> 
> Both hw/ide/core.c and hw/ide/macio.c also call dma_blk_io() but don't
> rely on it taking the AioContext lock, so this change is safe.
> 
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  system/dma-helpers.c | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.
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