From 61d7e2b266fe00b0af43ec53cca6ca694efb709e Mon Sep 17 00:00:00 2001
From: Hongbo Li <herberthbli@tencent.com>
Date: Wed, 1 Jul 2020 10:58:03 +0800
Subject: [PATCH] net: sched when reading tcp proc

cat /proc/net/tcp may cause long latency.
Add cond_resched() when reading this proc file.

Signed-off-by: Hongbo Li <herberthbli@tencent.com>
---
 include/net/tcp.h          | 1 +
 net/ipv4/sysctl_net_ipv4.c | 7 +++++++
 net/ipv4/tcp_ipv4.c        | 6 ++++++
 3 files changed, 14 insertions(+)

diff --git a/include/net/tcp.h b/include/net/tcp.h
index bb17aa302..ff22dad4f 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -278,6 +278,7 @@ extern int sysctl_tcp_loss_init_cwnd;
 extern int sysctl_tcp_init_cwnd;
 extern int sysctl_tcp_rto_min;
 extern int sysctl_tcp_rto_max;
+extern int sysctl_tcp_proc_sched;
 
 extern atomic_long_t tcp_memory_allocated;
 extern struct percpu_counter tcp_sockets_allocated;
diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index c286f88f1..a6f6b1af4 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -771,6 +771,13 @@ static struct ctl_table ipv4_table[] = {
 		.mode           = 0644,
 		.proc_handler   = proc_dointvec,
 	},
+	{
+		.procname	= "tcp_proc_sched",
+		.data		= &sysctl_tcp_proc_sched,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec,
+	},
 	{ }
 };
 
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 9c07e9fd8..ffb45284d 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -85,6 +85,8 @@
 #include <crypto/hash.h>
 #include <linux/scatterlist.h>
 
+int sysctl_tcp_proc_sched __read_mostly = 1;
+
 #ifdef CONFIG_TCP_MD5SIG
 static int tcp_v4_md5_hash_hdr(char *md5_hash, const struct tcp_md5sig_key *key,
 			       __be32 daddr, __be32 saddr, const struct tcphdr *th);
@@ -1966,6 +1968,8 @@ get_sk:
 			return sk;
 	}
 	spin_unlock(&ilb->lock);
+	if (sysctl_tcp_proc_sched)
+		cond_resched();
 	st->offset = 0;
 	if (++st->bucket < INET_LHTABLE_SIZE)
 		goto get_head;
@@ -2023,6 +2027,8 @@ static void *established_get_first(struct seq_file *seq)
 			goto out;
 		}
 		spin_unlock_bh(lock);
+		if (sysctl_tcp_proc_sched)
+			cond_resched();
 	}
 out:
 	return rc;