Re: [PATCH rdma-next 1/4] RDMA/mlx5: Use unsigned comparison in the CQ cleanup loop

[sashiko-bot@kernel.org]

> From: Yishai Hadas <yishaih@nvidia.com>
> 
> __mlx5_ib_cq_clean() sweeps the CQ backwards from the producer index
> down to the consumer index:
> 
>   while ((int) --prod_index - (int) cq->mcq.cons_index >= 0)
> 
> Both indexes are free running u32 counters, so the comparison has to
> be done modulo 2^32.  Casting each operand to int and subtracting
> does not do that: the subtraction overflows whenever the two indexes
> straddle 2^31, which is undefined behaviour, and a compiler that
> assumes signed overflow cannot occur is free to discard the
> subtraction and fold the expression into a plain signed comparison.
> That comparison is not wraparound safe.
> 
> [ ... ]
> exactly that many iterations regardless of whether either counter has
> wrapped, because the loop no longer compares magnitudes at all.
> 
> Signed-off-by: Yishai Hadas <yishaih@nvidia.com>
> Signed-off-by: Edward Srouji <edwards@nvidia.com>

Sashiko has reviewed this patch and found no issues. It looks great!

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260915-fix-cq-cleanup-v1-0-e991944cf898@nvidia.com?part=1