[PATCH 6.1 502/609] tcp: add a scheduling point in established_get_first()

6.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jian Wen <[email protected]>

[ Upstream commit 9f4a7c930284bf2b5b84d3636a8e88857149328f ]

Kubernetes[1] is going to stick with /proc/net/tcp for a while.

This commit reduces the scheduling latency introduced by
established_get_first(), similar to commit acffb584cda7 ("net: diag:
add a scheduling point in inet_diag_dump_icsk()").

In our environment, the scheduling latency affects the performance of
latency-sensitive services like Redis.

Changes in V2 :
 - call cond_resched() before checking if a bucket is empty as
   suggested by Eric Dumazet
 - removed the delay of synchronize_net() from the commit message

[1] https://github.com/google/cadvisor/blob/v0.47.2/container/libcontainer/handler.go#L130

Signed-off-by: Jian Wen <[email protected]>
Reviewed-by: Simon Horman <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>
Stable-dep-of: e5fd3f514e27 ("bpf: tcp: Fix use-after-free in bpf_iter_tcp_established_batch()")
Signed-off-by: Sasha Levin <[email protected]>
---
 net/ipv4/tcp_ipv4.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 00348cb9a211b..89200b4314018 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -57,6 +57,7 @@
 #include <linux/init.h>
 #include <linux/times.h>
 #include <linux/slab.h>
+#include <linux/sched.h>
 
 #include <net/net_namespace.h>
 #include <net/icmp.h>
@@ -2412,6 +2413,8 @@ static void *established_get_first(struct seq_file *seq)
 		struct hlist_nulls_node *node;
 		spinlock_t *lock = inet_ehash_lockp(hinfo, st->bucket);
 
+		cond_resched();
+
 		/* Lockless fast path for the common case of empty buckets */
 		if (empty_bucket(hinfo, st))
 			continue;
-- 
2.53.0