[PATCH] spin_unlock_bh() and preempt_check_resched()

In _spin_unlock_bh(lock):
	do { \
		_raw_spin_unlock(lock); \
		preempt_enable(); \
		local_bh_enable(); \
		__release(lock); \
	} while (0)

there is no reason for using preempt_enable() instead of a simple
preempt_enable_no_resched()

Since we know bottom halves are disabled, preempt_schedule() will always
return at once (preempt_count!=0), and hence preempt_check_resched() is
useless here...

This fixes it by using "preempt_enable_no_resched()" instead of the
"preempt_enable()", and thus avoids the useless preempt_check_resched()
just before re-enabling bottom halves.

Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 4 insertions, 4 deletions

diff --git a/include/linux/spinlock.h b/include/linux/spinlock.h
index e895f3eaf53a..d6ba068719b6 100644
--- a/include/linux/spinlock.h
+++ b/include/linux/spinlock.h
@@ -248,7 +248,7 @@ typedef struct {
 
 #define _spin_trylock_bh(lock)  ({preempt_disable(); local_bh_disable(); \
                                 _raw_spin_trylock(lock) ? \
-                                1 : ({preempt_enable(); local_bh_enable(); 0;});})
+                                1 : ({preempt_enable_no_resched(); local_bh_enable(); 0;});})
 
 #define _spin_lock(lock)        \
 do { \
@@ -383,7 +383,7 @@ do { \
 #define _spin_unlock_bh(lock) \
 do { \
         _raw_spin_unlock(lock); \
-        preempt_enable(); \
+        preempt_enable_no_resched(); \
         local_bh_enable(); \
         __release(lock); \
 } while (0)
@@ -391,7 +391,7 @@ do { \
 #define _write_unlock_bh(lock) \
 do { \
         _raw_write_unlock(lock); \
-        preempt_enable(); \
+        preempt_enable_no_resched(); \
         local_bh_enable(); \
         __release(lock); \
 } while (0)
@@ -423,8 +423,8 @@ do { \
 #define _read_unlock_bh(lock)   \
 do { \
         _raw_read_unlock(lock); \
+        preempt_enable_no_resched();    \
         local_bh_enable();      \
-        preempt_enable();       \
         __release(lock); \
 } while (0)