linux-kernel - [tip: locking/urgent] u64_stats,lockdep: Fix u64_stats

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Message-ID: <161537557688.398.9814412263245097413.tip-bot2@tip-bot2>
Date:   Wed, 10 Mar 2021 11:26:16 -0000
From:   "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Jakub Kicinski <kuba@...nel.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        "Erhard F." <erhard_f@...lbox.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: locking/urgent] u64_stats,lockdep: Fix u64_stats_init() vs lockdep

The following commit has been merged into the locking/urgent branch of tip:

Commit-ID:     d5b0e0677bfd5efd17c5bbb00156931f0d41cb85
Gitweb:        https://git.kernel.org/tip/d5b0e0677bfd5efd17c5bbb00156931f0d41cb85
Author:        Peter Zijlstra <peterz@...radead.org>
AuthorDate:    Mon, 08 Mar 2021 09:38:12 +01:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Wed, 10 Mar 2021 09:51:45 +01:00

u64_stats,lockdep: Fix u64_stats_init() vs lockdep

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
---
 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 c6abb79..e81856c 100644
--- a/include/linux/u64_stats_sync.h
+++ b/include/linux/u64_stats_sync.h
@@ -115,12 +115,13 @@ static inline void u64_stats_inc(u64_stats_t *p)
 }
 #endif
 
+#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)
 {