netdev - [PATCH net] tcp: Add READ_ONCE() to read tcp_orphan

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Date:   Thu, 12 May 2022 18:33:21 +0800
From:   Liu Jian <liujian56@...wei.com>
To:     <edumazet@...gle.com>, <davem@...emloft.net>,
        <yoshfuji@...ux-ipv6.org>, <dsahern@...nel.org>, <kuba@...nel.org>,
        <pabeni@...hat.com>, <ncardwell@...gle.com>,
        <netdev@...r.kernel.org>
CC:     <liujian56@...wei.com>
Subject: [PATCH net] tcp: Add READ_ONCE() to read tcp_orphan_count

The tcp_orphan_count per-CPU variable is read locklessly, so this commit
add the READ_ONCE() to a load in order to avoid below KCSAN warnning:

BUG: KCSAN: data-race in tcp_orphan_count_sum net/ipv4/tcp.c:2476 [inline]
BUG: KCSAN: data-race in tcp_orphan_update+0x64/0x100 net/ipv4/tcp.c:2487

race at unknown origin, with read to 0xffff9c63bbdac7a8 of 4 bytes by interrupt on cpu 2:
 tcp_orphan_count_sum net/ipv4/tcp.c:2476 [inline]
 tcp_orphan_update+0x64/0x100 net/ipv4/tcp.c:2487
 call_timer_fn+0x33/0x210 kernel/time/timer.c:1414

Fixes: 19757cebf0c5 ("tcp: switch orphan_count to bare per-cpu counters")
Signed-off-by: Liu Jian <liujian56@...wei.com>
---
 net/ipv4/tcp.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index cf18fbcbf123..7245609f41e6 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2718,7 +2718,7 @@ int tcp_orphan_count_sum(void)
 	int i, total = 0;
 
 	for_each_possible_cpu(i)
-		total += per_cpu(tcp_orphan_count, i);
+		total += READ_ONCE(per_cpu(tcp_orphan_count, i));
 
 	return max(total, 0);
 }
-- 
2.17.1