Commit 4999201a authored Aug 08, 2014 by Bart Van Assche Committed by Ingo Molnar Aug 13, 2014

locking/spinlocks: Always evaluate the second argument of spin_lock_nested()



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().

An intentional side effect of this patch is 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@acm.org>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: David Rientjes <rientjes@google.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/53E4A7F8.1040700@acm.org


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 0a7cbf9a

include/linux/spinlock.h

+7 −1

Original line number	Diff line number	Diff line
		@@ -197,7 +197,13 @@ 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)
		/*
		* Always evaluate the 'subclass' argument to avoid that the compiler
		* warns about set-but-not-used variables when building with
		* CONFIG_DEBUG_LOCK_ALLOC=n and with W=1.
		*/
		# define raw_spin_lock_nested(lock, subclass) \
		_raw_spin_lock(((void)(subclass), (lock)))
		# define raw_spin_lock_nest_lock(lock, nest_lock) _raw_spin_lock(lock)
		#endif