linux-kernel - [PATCH] spin_lock_*(): Always evaluate second argument

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Message-ID: <539ED993.80807@acm.org>
Date:	Mon, 16 Jun 2014 13:48:35 +0200
From:	Bart Van Assche <bvanassche@....org>
To:	Ingo Molnar <mingo@...nel.org>
CC:	Peter Zijlstra <peterz@...radead.org>,
	"David S. Miller" <davem@...emloft.net>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: [PATCH] spin_lock_*(): Always evaluate second argument

Evaluating a macro argument only if certain configuration options
have been selected is confusing and error-prone. Hence always
evaluate the second argument of spin_lock_nested() and
spin_lock_nest_lock().

This patch has the intentional side effect that it avoids that the
following warning is reported for netif_addr_lock_nested() when
building with CONFIG_DEBUG_LOCK_ALLOC=n and with W=1:

include/linux/netdevice.h: In function 'netif_addr_lock_nested':
include/linux/netdevice.h:2865:6: warning: variable 'subclass' set but not used [-Wunused-but-set-variable]
  int subclass = SINGLE_DEPTH_NESTING;
      ^

Signed-off-by: Bart Van Assche <bvanassche@....org>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: David S. Miller <davem@...emloft.net>
---
 include/linux/spinlock.h | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/include/linux/spinlock.h b/include/linux/spinlock.h
index 3f2867f..32b16cc 100644
--- a/include/linux/spinlock.h
+++ b/include/linux/spinlock.h
@@ -197,8 +197,10 @@ static inline void do_raw_spin_unlock(raw_spinlock_t *lock) __releases(lock)
 		 _raw_spin_lock_nest_lock(lock, &(nest_lock)->dep_map);	\
 	 } while (0)
 #else
-# define raw_spin_lock_nested(lock, subclass)		_raw_spin_lock(lock)
-# define raw_spin_lock_nest_lock(lock, nest_lock)	_raw_spin_lock(lock)
+# define raw_spin_lock_nested(lock, subclass)		\
+	((void)(subclass), _raw_spin_lock(lock))
+# define raw_spin_lock_nest_lock(lock, nest_lock)	\
+	((void)(nest_lock), _raw_spin_lock(lock))
 #endif
 
 #if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
-- 
1.8.4.5

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