linux-kernel - [PATCH net] u64_stats: fix u64_stats_init() for lockdep when used repeatedly in one file

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Date: Thu,  4 Apr 2024 09:57:40 +0200
From: Petr Tesarik <petr@...arici.cz>
To: "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	netdev@...r.kernel.org (open list)
Cc: Linux regressions mailing list <regressions@...ts.linux.dev>,
	linux-kernel@...r.kernel.org (open list),
	"Linux regression tracking (Thorsten Leemhuis)" <regressions@...mhuis.info>,
	Petr Tesarik <petr@...arici.cz>
Subject: [PATCH net] u64_stats: fix u64_stats_init() for lockdep when used repeatedly in one file

Fix bogus lockdep warnings if multiple u64_stats_sync variables are
initialized in the same file.

With CONFIG_LOCKDEP, seqcount_init() is a macro which declares:

	static struct lock_class_key __key;

Since u64_stats_init() is a function (albeit an inline one), all calls
within the same file end up using the same instance, effectively treating
them all as a single lock-class.

Fixes: 9464ca650008 ("net: make u64_stats_init() a function")
Closes: https://lore.kernel.org/netdev/ea1567d9-ce66-45e6-8168-ac40a47d1821@roeck-us.net/
Signed-off-by: Petr Tesarik <petr@...arici.cz>
---
 include/linux/u64_stats_sync.h | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/include/linux/u64_stats_sync.h b/include/linux/u64_stats_sync.h
index ffe48e69b3f3..457879938fc1 100644
--- a/include/linux/u64_stats_sync.h
+++ b/include/linux/u64_stats_sync.h
@@ -135,10 +135,11 @@ static inline void u64_stats_inc(u64_stats_t *p)
 	p->v++;
 }
 
-static inline void u64_stats_init(struct u64_stats_sync *syncp)
-{
-	seqcount_init(&syncp->seq);
-}
+#define u64_stats_init(syncp)				\
+	do {						\
+		struct u64_stats_sync *__s = (syncp);	\
+		seqcount_init(&__s->seq);		\
+	} while (0)
 
 static inline void __u64_stats_update_begin(struct u64_stats_sync *syncp)
 {
-- 
2.44.0