Re: [PATCH 087/104] virtiofsd: prevent fv_queue_thread() vs virtio_loop() races

[Daniel P . Berrangé]

On Thu, Dec 12, 2019 at 04:38:47PM +0000, Dr. David Alan Gilbert (git) wrote:
> From: Stefan Hajnoczi <address@hidden>
> 
> We call into libvhost-user from the virtqueue handler thread and the
> vhost-user message processing thread without a lock.  There is nothing
> protecting the virtqueue handler thread if the vhost-user message
> processing thread changes the virtqueue or memory table while it is
> running.
> 
> This patch introduces a read-write lock.  Virtqueue handler threads are
> readers.  The vhost-user message processing thread is a writer.  This
> will allow concurrency for multiqueue in the future while protecting
> against fv_queue_thread() vs virtio_loop() races.
> 
> Note that the critical sections could be made smaller but it would be
> more invasive and require libvhost-user changes.  Let's start simple and
> improve performance later, if necessary.  Another option would be an
> RCU-style approach with lighter-weight primitives.
> 
> Signed-off-by: Stefan Hajnoczi <address@hidden>
>   Merged with log changes
>   pull request 12

Two extraneous lines

> ---
>  tools/virtiofsd/fuse_virtio.c | 34 +++++++++++++++++++++++++++++++++-
>  1 file changed, 33 insertions(+), 1 deletion(-)

Reviewed-by: Daniel P. Berrangé <address@hidden>


Regards,
Daniel
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