[PATCH AUTOSEL 5.4 26/37] u64_stats,lockdep: Fix u64_stats_init() vs lockdep

Sasha Levin
2021-03-17T01:03:34Z

From: Peter Zijlstra <peterz@infradead.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@kernel.org>
Debugged-by: "Ahmed S. Darwish" <a.darwish@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: "Erhard F." <erhard_f@mailbox.org>
Link: https://lkml.kernel.org/r/YEXicy6+9MksdLZh@hirez.programming.kicks-ass.net
Signed-off-by: Sasha Levin <sashal@kernel.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 a27604f99ed0..11096b561dab 100644
--- a/include/linux/u64_stats_sync.h
+++ b/include/linux/u64_stats_sync.h
@@ -69,12 +69,13 @@ 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