5.15-stable review patch. If anyone has any objections, please let me know.
------------------
From: Eric Dumazet <edumazet@xxxxxxxxxx>
[ Upstream commit cd42ba1c8ac9deb9032add6adf491110e7442040 ]
This came while reviewing commit c4e86b4363ac ("net: add two more
call_rcu_hurry()").
Paolo asked if adding one synchronize_rcu() would help.
While synchronize_rcu() does not help, making sure to call
rcu_barrier() before msleep(wait) is definitely helping
to make sure lazy call_rcu() are completed.
Instead of waiting ~100 seconds in my tests, the ref_tracker
splats occurs one time only, and netdev_wait_allrefs_any()
latency is reduced to the strict minimum.
Ideally we should audit our call_rcu() users to make sure
no refcount (or cascading call_rcu()) is held too long,
because rcu_barrier() is quite expensive.
Fixes: 0e4be9e57e8c ("net: use exponential backoff in netdev_wait_allrefs")
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Link: https://lore.kernel.org/all/28bbf698-befb-42f6-b561-851c67f464aa@xxxxxxxxxx/T/#m76d73ed6b03cd930778ac4d20a777f22a08d6824
Reviewed-by: Jiri Pirko <jiri@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
net/core/dev.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/net/core/dev.c b/net/core/dev.c
index f80bc2ca888aa..e86ef1a1647ec 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -10549,8 +10549,9 @@ static void netdev_wait_allrefs(struct net_device *dev)
rebroadcast_time = jiffies;
}
+ rcu_barrier();
+
if (!wait) {
- rcu_barrier();
wait = WAIT_REFS_MIN_MSECS;
} else {
msleep(wait);
--
2.43.0
