On Thu, Jun 20, 2024 at 07:09:08AM -0700, Jakub Kicinski wrote:

On Wed, 19 Jun 2024 10:55:29 +0800 Li RongQing wrote:

quoted

This place is fetching the stats, so u64_stats_fetch_begin
and u64_stats_fetch_retry should be used

Fixes: 6208799553a8 ("virtio-net: support rx netdim")
Signed-off-by: Li RongQing <redacted>
---
 drivers/net/virtio_net.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 61a57d1..b669e73 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c

@@ -2332,16 +2332,18 @@ static void virtnet_poll_cleantx(struct receive_queue *rq)
 static void virtnet_rx_dim_update(struct virtnet_info *vi, struct receive_queue *rq)
 {
 	struct dim_sample cur_sample = {};
+	unsigned int start;
 
 	if (!rq->packets_in_napi)
 		return;
 
-	u64_stats_update_begin(&rq->stats.syncp);
-	dim_update_sample(rq->calls,
-			  u64_stats_read(&rq->stats.packets),
-			  u64_stats_read(&rq->stats.bytes),
-			  &cur_sample);
-	u64_stats_update_end(&rq->stats.syncp);
+	do {
+		start = u64_stats_fetch_begin(&rq->stats.syncp);
+		dim_update_sample(rq->calls,
+				u64_stats_read(&rq->stats.packets),
+				u64_stats_read(&rq->stats.bytes),
+				&cur_sample);
+	} while (u64_stats_fetch_retry(&rq->stats.syncp, start));

Did you by any chance use an automated tool of any sort to find this
issue or generate the fix?

I don't think this is actually necessary here, you're in the same
context as the updater of the stats, you don't need any protection.
You can remove u64_stats_update_begin() / end() (in net-next, there's
no bug).

I won't comment on implications of calling dim_update_sample() in 
a loop.

I didn't realize there are any - it seems to be idempotent, no?

Please make sure you answer my "did you use a tool" question, I'm
really curious.
-- 
pw-bot: cr