On Mon, Mar 08, 2021 at 09:42:08PM +0100, Erhard F. wrote:
> I can confirm that your patch on top of 5.12-rc2 makes the lockdep
> splat disappear (Ahmeds' 1st patch not installed).
Excellent, I'll queue the below in locking/urgent then.
---
Subject: u64_stats,lockdep: Fix u64_stats_init() vs lockdep
From: Peter Zijlstra <pet...@infradead.org>
Date: Mon, 8 Mar 2021 09:38:12 +0100
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 <k...@kernel.org>
Debugged-by: "Ahmed S. Darwish" <a.darw...@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
Tested-by: "Erhard F." <erhar...@mailbox.org>
Link: https://lkml.kernel.org/r/yexicy6+9mksd...@hirez.programming.kicks-ass.net
---
include/linux/u64_stats_sync.h | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
--- 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_sta
}
#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)
{
