Backmerge tag 'v7.3-rc4' into drm-next

Linux 7.3-rc4

Requested by Philipp Stanner for
2ab510e63197360945f915dd5631a77c63ac6b27 would be needed as a groundlayer
for further patches that extend the locking in drm_sched

Signed-off-by: Dave Airlie <airlied@redhat.com>

1 files changed, 15 insertions, 1 deletions

diff --git a/include/net/codel_impl.h b/include/net/codel_impl.h
index 2c1f0ec309e9..8f26132d45b7 100644
--- a/include/net/codel_impl.h
+++ b/include/net/codel_impl.h
@@ -93,12 +93,17 @@ static void codel_Newton_step(struct codel_vars *vars)
  * CoDel control_law is t + interval/sqrt(count)
  * We maintain in rec_inv_sqrt the reciprocal value of sqrt(count) to avoid
  * both sqrt() and divide operation.
+ *
+ * Clamp the increment to at least 1 tick: a very small interval (or a
+ * large count) can truncate it to zero, stalling the dropping loop.
  */
 static codel_time_t codel_control_law(codel_time_t t,
 				      codel_time_t interval,
 				      u32 rec_inv_sqrt)
 {
-	return t + reciprocal_scale(interval, rec_inv_sqrt << REC_INV_SQRT_SHIFT);
+	return t + max_t(u32, 1,
+			 reciprocal_scale(interval,
+					  rec_inv_sqrt << REC_INV_SQRT_SHIFT));
 }
 
 static bool codel_should_drop(const struct sk_buff *skb,
@@ -154,6 +159,7 @@ static struct sk_buff *codel_dequeue(void *ctx,
 				     codel_skb_dequeue_t dequeue_func)
 {
 	struct sk_buff *skb = dequeue_func(vars, ctx);
+	unsigned int drops = 0;
 	codel_time_t now;
 	bool drop;
 
@@ -180,6 +186,14 @@ static struct sk_buff *codel_dequeue(void *ctx,
 			 */
 			while (vars->dropping &&
 			       codel_time_after_eq(now, vars->drop_next)) {
+				if (++drops > CODEL_MAX_DROPS_PER_DEQUEUE) {
+					/* fell far behind the schedule */
+					WRITE_ONCE(vars->drop_next,
+						   codel_control_law(now,
+								     params->interval,
+								     vars->rec_inv_sqrt));
+					break;
+				}
 				/* dont care of possible wrap
 				 * since there is no more divide.
 				 */