Re: [PATCH v2 for-7.1 5/9] nbd: use a QemuMutex to synchronize yanking, reconnection and coroutines

[Eric Blake]

On Thu, Apr 14, 2022 at 07:57:52PM +0200, Paolo Bonzini wrote:
> The condition for waiting on the s->free_sema queue depends on
> both s->in_flight and s->state.  The latter is currently using
> atomics, but this is quite dubious and probably wrong.
> 
> Because s->state is written in the main thread too, for example by
> the yank callback, it cannot be protected by a CoMutex.  Introduce a
> separate lock that can be used by nbd_co_send_request(); later on this
> lock will also be used for s->state.  There will not be any contention
> on the lock unless there is a yank or reconnect, so this is not
> performance sensitive.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  block/nbd.c | 46 +++++++++++++++++++++++++++-------------------
>  1 file changed, 27 insertions(+), 19 deletions(-)

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

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
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