RDMA/mlx4: Use unsigned comparison in the CQ cleanup loop

__mlx4_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.

The kernel is built with -fno-strict-overflow, so gcc and clang both
retain the subtraction today and the generated code is unaffected;
there is no known user-visible impact from the current code.  Still,
correctness here shouldn't depend on that build flag.

Replace the loop with a plain unsigned equality check instead:

  while (prod_index != cq->mcq.cons_index) {
          --prod_index;
          ...

The preceding forward scan starts prod_index at cons_index and stops no
later than cons_index + cq->ibcq.cqe, so the two indexes are at most
cq->ibcq.cqe apart.  Decrementing prod_index reaches cons_index in
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>
Link: https://patch.msgid.link/20260915-fix-cq-cleanup-v1-2-e991944cf898@nvidia.com
Signed-off-by: Leon Romanovsky <leon@kernel.org>

0 files changed, 0 insertions, 0 deletions