[PATCH 1/2 v2] lockdep: Fix redundant_hardirqs_on incremented with irqs enabled

[PATCH 1/2 v2] lockdep: Fix redundant_hardirqs_on incremented with irqs enabled

[Frederic Weisbecker]

When a path restore the flags while irqs are already enabled, we
update the per cpu var redundant_hardirqs_on in a racy fashion
and debug_atomic_inc() warns about this situation.

In this particular case, loosing a few hits in a stat is not a big
deal, so increment it without protection.

v2: Don't bother with disabling irq, we can miss one count in
    rare situations

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: David Miller <davem@davemloft.net>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
---
 kernel/lockdep.c |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletions(-)

diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index 78325f8..1b58a1b 100644
--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -2298,7 +2298,12 @@ void trace_hardirqs_on_caller(unsigned long ip)
 		return;
 
 	if (unlikely(curr->hardirqs_enabled)) {
-		debug_atomic_inc(redundant_hardirqs_on);
+		/*
+		 * Neither irq nor preemption are disabled here
+		 * so this is racy by nature but loosing one hit
+		 * in a stat is not a big deal.
+		 */
+		this_cpu_inc(lockdep_stats.redundant_hardirqs_on);
 		return;
 	}
 	/* we'll do an OFF -> ON transition: */
-- 
1.6.2.3

[PATCH 2/2] lockdep: Simplify debug atomic ops

[Frederic Weisbecker]

Simplify debug_atomic_inc/dec by using this_cpu_inc/dec() instead
of doing it through an indirect get_cpu_var() and a manual
incrementation.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
---
 kernel/lockdep_internals.h |   10 ++--------
 1 files changed, 2 insertions(+), 8 deletions(-)

diff --git a/kernel/lockdep_internals.h b/kernel/lockdep_internals.h
index 8d7d4b6..2b17476 100644
--- a/kernel/lockdep_internals.h
+++ b/kernel/lockdep_internals.h
@@ -140,19 +140,13 @@ struct lockdep_stats {
 DECLARE_PER_CPU(struct lockdep_stats, lockdep_stats);
 
 #define debug_atomic_inc(ptr)			{		\
-	struct lockdep_stats *__cpu_lockdep_stats;		\
-								\
 	WARN_ON_ONCE(!irqs_disabled());				\
-	__cpu_lockdep_stats = &__get_cpu_var(lockdep_stats);	\
-	__cpu_lockdep_stats->ptr++;				\
+	this_cpu_inc(lockdep_stats.ptr);			\
 }
 
 #define debug_atomic_dec(ptr)			{		\
-	struct lockdep_stats *__cpu_lockdep_stats;		\
-								\
 	WARN_ON_ONCE(!irqs_disabled());				\
-	__cpu_lockdep_stats = &__get_cpu_var(lockdep_stats);	\
-	__cpu_lockdep_stats->ptr--;				\
+	this_cpu_inc(lockdep_stats.ptr);			\
 }
 
 #define debug_atomic_read(ptr)		({				\
-- 
1.6.2.3