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SubjectRe: [PATCH 3/5] Drivers: hv: vmbus: Fix a bug in hv_need_to_signal_on_read()
Date
"K. Y. Srinivasan" <kys@microsoft.com> writes:

> We need to issue a full memory barrier prior making a signalling
> decision.

Any reason this should be mb()? This is pretty strong and will probably
lead to performace regression ... and, btw, we have another mb() in
hv_ringbuffer_read().

Could you please describe the scenarion you're trying to protect against
so we could search for a better solution?

>
> Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
> Cc: stable@vger.kernel.org
> ---
> drivers/hv/ring_buffer.c | 1 +
> 1 files changed, 1 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/hv/ring_buffer.c b/drivers/hv/ring_buffer.c
> index 2919395..67dc245 100644
> --- a/drivers/hv/ring_buffer.c
> +++ b/drivers/hv/ring_buffer.c
> @@ -104,6 +104,7 @@ static bool hv_need_to_signal_on_read(struct hv_ring_buffer_info *rbi)
> u32 cur_write_sz;
> u32 pending_sz;
>
> + mb();
> pending_sz = READ_ONCE(rbi->ring_buffer->pending_send_sz);
> /* If the other end is not blocked on write don't bother. */
> if (pending_sz == 0)

--
Vitaly

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