[PATCH net] linux/dim: Do nothing if no time delta between samples

[Tariq Toukan <tariqt@nvidia.com>]

From: Roy Novich <royno@nvidia.com>

Add return value for dim_calc_stats. This is an indication for the
caller if curr_stats was assigned by the function. Avoid using
curr_stats uninitialized over {rdma/net}_dim, when no time delta between
samples. Coverity reported this potential use of an uninitialized
variable.

Fixes: 4c4dbb4a7363 ("net/mlx5e: Move dynamic interrupt coalescing code to include/linux")
Fixes: cb3c7fd4f839 ("net/mlx5e: Support adaptive RX coalescing")
Signed-off-by: Roy Novich <royno@nvidia.com>
Reviewed-by: Aya Levin <ayal@nvidia.com>
Reviewed-by: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
---
 include/linux/dim.h | 3 ++-
 lib/dim/dim.c       | 5 +++--
 lib/dim/net_dim.c   | 3 ++-
 lib/dim/rdma_dim.c  | 3 ++-
 4 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/include/linux/dim.h b/include/linux/dim.h
index 6c5733981563..f343bc9aa2ec 100644
--- a/include/linux/dim.h
+++ b/include/linux/dim.h
@@ -236,8 +236,9 @@ void dim_park_tired(struct dim *dim);
  *
  * Calculate the delta between two samples (in data rates).
  * Takes into consideration counter wrap-around.
+ * Returned boolean indicates whether curr_stats are reliable.
  */
-void dim_calc_stats(struct dim_sample *start, struct dim_sample *end,
+bool dim_calc_stats(struct dim_sample *start, struct dim_sample *end,
 		    struct dim_stats *curr_stats);
 
 /**
diff --git a/lib/dim/dim.c b/lib/dim/dim.c
index 38045d6d0538..e89aaf07bde5 100644
--- a/lib/dim/dim.c
+++ b/lib/dim/dim.c
@@ -54,7 +54,7 @@ void dim_park_tired(struct dim *dim)
 }
 EXPORT_SYMBOL(dim_park_tired);
 
-void dim_calc_stats(struct dim_sample *start, struct dim_sample *end,
+bool dim_calc_stats(struct dim_sample *start, struct dim_sample *end,
 		    struct dim_stats *curr_stats)
 {
 	/* u32 holds up to 71 minutes, should be enough */
@@ -66,7 +66,7 @@ void dim_calc_stats(struct dim_sample *start, struct dim_sample *end,
 			     start->comp_ctr);
 
 	if (!delta_us)
-		return;
+		return false;
 
 	curr_stats->ppms = DIV_ROUND_UP(npkts * USEC_PER_MSEC, delta_us);
 	curr_stats->bpms = DIV_ROUND_UP(nbytes * USEC_PER_MSEC, delta_us);
@@ -79,5 +79,6 @@ void dim_calc_stats(struct dim_sample *start, struct dim_sample *end,
 	else
 		curr_stats->cpe_ratio = 0;
 
+	return true;
 }
 EXPORT_SYMBOL(dim_calc_stats);
diff --git a/lib/dim/net_dim.c b/lib/dim/net_dim.c
index 53f6b9c6e936..4e32f7aaac86 100644
--- a/lib/dim/net_dim.c
+++ b/lib/dim/net_dim.c
@@ -227,7 +227,8 @@ void net_dim(struct dim *dim, struct dim_sample end_sample)
 				  dim->start_sample.event_ctr);
 		if (nevents < DIM_NEVENTS)
 			break;
-		dim_calc_stats(&dim->start_sample, &end_sample, &curr_stats);
+		if (!dim_calc_stats(&dim->start_sample, &end_sample, &curr_stats))
+			break;
 		if (net_dim_decision(&curr_stats, dim)) {
 			dim->state = DIM_APPLY_NEW_PROFILE;
 			schedule_work(&dim->work);
diff --git a/lib/dim/rdma_dim.c b/lib/dim/rdma_dim.c
index 15462d54758d..88f779486707 100644
--- a/lib/dim/rdma_dim.c
+++ b/lib/dim/rdma_dim.c
@@ -88,7 +88,8 @@ void rdma_dim(struct dim *dim, u64 completions)
 		nevents = curr_sample->event_ctr - dim->start_sample.event_ctr;
 		if (nevents < DIM_NEVENTS)
 			break;
-		dim_calc_stats(&dim->start_sample, curr_sample, &curr_stats);
+		if (!dim_calc_stats(&dim->start_sample, curr_sample, &curr_stats))
+			break;
 		if (rdma_dim_decision(&curr_stats, dim)) {
 			dim->state = DIM_APPLY_NEW_PROFILE;
 			schedule_work(&dim->work);
-- 
2.34.1