linux-kernel - [PATCH AUTOSEL 4.4 11/14] u64_stats,lockdep: Fix u64_stats

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Message-Id: <20210317010008.727496-11-sashal@kernel.org>
Date:   Tue, 16 Mar 2021 21:00:05 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Jakub Kicinski <kuba@...nel.org>,
        "Ahmed S. Darwish" <a.darwish@...utronix.de>,
        "Erhard F." <erhard_f@...lbox.org>, Sasha Levin <sashal@...nel.org>
Subject: [PATCH AUTOSEL 4.4 11/14] u64_stats,lockdep: Fix u64_stats_init() vs lockdep

From: Peter Zijlstra <peterz@...radead.org>

[ Upstream commit d5b0e0677bfd5efd17c5bbb00156931f0d41cb85 ]

Jakub reported that:

    static struct net_device *rtl8139_init_board(struct pci_dev *pdev)
    {
	    ...
	    u64_stats_init(&tp->rx_stats.syncp);
	    u64_stats_init(&tp->tx_stats.syncp);
	    ...
    }

results in lockdep getting confused between the RX and TX stats lock.
This is because u64_stats_init() is an inline calling seqcount_init(),
which is a macro using a static variable to generate a lockdep class.

By wrapping that in an inline, we negate the effect of the macro and
fold the static key variable, hence the confusion.

Fix by also making u64_stats_init() a macro for the case where it
matters, leaving the other case an inline for argument validation
etc.

Reported-by: Jakub Kicinski <kuba@...nel.org>
Debugged-by: "Ahmed S. Darwish" <a.darwish@...utronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Tested-by: "Erhard F." <erhard_f@...lbox.org>
Link: https://lkml.kernel.org/r/YEXicy6+9MksdLZh@hirez.programming.kicks-ass.net
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 include/linux/u64_stats_sync.h | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/include/linux/u64_stats_sync.h b/include/linux/u64_stats_sync.h
index df89c9bcba7d..7b38288dc239 100644
--- a/include/linux/u64_stats_sync.h
+++ b/include/linux/u64_stats_sync.h
@@ -68,12 +68,13 @@ struct u64_stats_sync {
 };
 
 
+#if BITS_PER_LONG == 32 && defined(CONFIG_SMP)
+#define u64_stats_init(syncp)	seqcount_init(&(syncp)->seq)
+#else
 static inline void u64_stats_init(struct u64_stats_sync *syncp)
 {
-#if BITS_PER_LONG == 32 && defined(CONFIG_SMP)
-	seqcount_init(&syncp->seq);
-#endif
 }
+#endif
 
 static inline void u64_stats_update_begin(struct u64_stats_sync *syncp)
 {
-- 
2.30.1