[PATCH v3] net/irda: fix lockdep annotation

[Dmitry Vyukov <dvyukov@google.com>]

The current annotation uses a global variable as recursion counter.
The variable is not atomic nor protected with a mutex, but mutated
by multiple threads. This causes lockdep bug reports episodically:

BUG: looking up invalid subclass: 4294967295
...
_raw_spin_lock_irqsave_nested+0x120/0x180
hashbin_delete+0x4fe/0x750
__irias_delete_object+0xab/0x170
irias_delete_object+0x5f/0xc0
ircomm_tty_detach_cable+0x1d5/0x3f0
...

Make the hashbin_lock_depth variable atomic to prevent bug reports.

As is this causes "unused variable 'depth'" warning without LOCKDEP.
So also change raw_spin_lock_irqsave_nested() macro to not cause
the warning without LOCKDEP. Similar to what raw_spin_lock_nested()
already does.

Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Dave Jones <davej@redhat.com>
Cc: Samuel Ortiz <samuel@sortiz.org>
Cc: David S. Miller <davem@davemloft.net>
Cc: netdev@vger.kernel.org
Fixes: c7630a4b932af ("[IrDA]: irda lockdep annotation")

---

Changes since v1:
 - Added raw_spin_lock_irqsave_nested() change
   as 0-DAY bot reported compiler warning without LOCKDEP.

Changes since v2:
 - Use ((void)(subclass), (lock)) instead of (void)subclass
   to prevent unused variable warning. Now 0-DAY complaints
   "error: void value not ignored as it ought to be".
   My compiler does not produce warning with W=1 either way,
   but the comma trick is what already used in raw_spin_lock_nested().
---
 include/linux/spinlock.h |  2 +-
 net/irda/irqueue.c       | 12 +++++++-----
 2 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/include/linux/spinlock.h b/include/linux/spinlock.h
index 47dd0cebd204..beeb5a39bd8b 100644
--- a/include/linux/spinlock.h
+++ b/include/linux/spinlock.h
@@ -218,7 +218,7 @@ static inline void do_raw_spin_unlock(raw_spinlock_t *lock) __releases(lock)
 #define raw_spin_lock_irqsave_nested(lock, flags, subclass)		\
 	do {								\
 		typecheck(unsigned long, flags);			\
-		flags = _raw_spin_lock_irqsave(lock);			\
+		flags = _raw_spin_lock_irqsave(((void)(subclass), (lock))); \
 	} while (0)
 #endif
 
diff --git a/net/irda/irqueue.c b/net/irda/irqueue.c
index acbe61c7e683..b9fd74e6ca99 100644
--- a/net/irda/irqueue.c
+++ b/net/irda/irqueue.c
@@ -384,21 +384,23 @@ EXPORT_SYMBOL(hashbin_new);
  *    just supply kfree, which should take care of the job.
  */
 #ifdef CONFIG_LOCKDEP
-static int hashbin_lock_depth = 0;
+static atomic_t hashbin_lock_depth = ATOMIC_INIT(0);
 #endif
 int hashbin_delete( hashbin_t* hashbin, FREE_FUNC free_func)
 {
 	irda_queue_t* queue;
 	unsigned long flags = 0;
-	int i;
+	int i, depth = 0;
 
 	IRDA_ASSERT(hashbin != NULL, return -1;);
 	IRDA_ASSERT(hashbin->magic == HB_MAGIC, return -1;);
 
 	/* Synchronize */
 	if ( hashbin->hb_type & HB_LOCK ) {
-		spin_lock_irqsave_nested(&hashbin->hb_spinlock, flags,
-					 hashbin_lock_depth++);
+#ifdef CONFIG_LOCKDEP
+		depth = atomic_inc_return(&hashbin_lock_depth) - 1;
+#endif
+		spin_lock_irqsave_nested(&hashbin->hb_spinlock, flags, depth);
 	}
 
 	/*
@@ -423,7 +425,7 @@ int hashbin_delete( hashbin_t* hashbin, FREE_FUNC free_func)
 	if ( hashbin->hb_type & HB_LOCK) {
 		spin_unlock_irqrestore(&hashbin->hb_spinlock, flags);
 #ifdef CONFIG_LOCKDEP
-		hashbin_lock_depth--;
+		atomic_dec(&hashbin_lock_depth);
 #endif
 	}
 
-- 
2.11.0.483.g087da7b7c-goog