The sleeping functions down, down_interruptible, down_killable and down_timeout can't be called with interrupts disabled, so we don't have to save and restore interrupt flag.
This patch avoids the costly pushf and popf instructions on the semaphore path. Signed-off-by: Mikulas Patocka <mpato...@redhat.com> --- kernel/locking/semaphore.c | 21 ++++++++------------- 1 file changed, 8 insertions(+), 13 deletions(-) Index: linux-2.6/kernel/locking/semaphore.c =================================================================== --- linux-2.6.orig/kernel/locking/semaphore.c 2017-06-03 00:22:44.000000000 +0200 +++ linux-2.6/kernel/locking/semaphore.c 2018-05-30 14:46:35.000000000 +0200 @@ -53,14 +53,12 @@ static noinline void __up(struct semapho */ void down(struct semaphore *sem) { - unsigned long flags; - - raw_spin_lock_irqsave(&sem->lock, flags); + raw_spin_lock_irq(&sem->lock); if (likely(sem->count > 0)) sem->count--; else __down(sem); - raw_spin_unlock_irqrestore(&sem->lock, flags); + raw_spin_unlock_irq(&sem->lock); } EXPORT_SYMBOL(down); @@ -75,15 +73,14 @@ EXPORT_SYMBOL(down); */ int down_interruptible(struct semaphore *sem) { - unsigned long flags; int result = 0; - raw_spin_lock_irqsave(&sem->lock, flags); + raw_spin_lock_irq(&sem->lock); if (likely(sem->count > 0)) sem->count--; else result = __down_interruptible(sem); - raw_spin_unlock_irqrestore(&sem->lock, flags); + raw_spin_unlock_irq(&sem->lock); return result; } @@ -101,15 +98,14 @@ EXPORT_SYMBOL(down_interruptible); */ int down_killable(struct semaphore *sem) { - unsigned long flags; int result = 0; - raw_spin_lock_irqsave(&sem->lock, flags); + raw_spin_lock_irq(&sem->lock); if (likely(sem->count > 0)) sem->count--; else result = __down_killable(sem); - raw_spin_unlock_irqrestore(&sem->lock, flags); + raw_spin_unlock_irq(&sem->lock); return result; } @@ -155,15 +151,14 @@ EXPORT_SYMBOL(down_trylock); */ int down_timeout(struct semaphore *sem, long timeout) { - unsigned long flags; int result = 0; - raw_spin_lock_irqsave(&sem->lock, flags); + raw_spin_lock_irq(&sem->lock); if (likely(sem->count > 0)) sem->count--; else result = __down_timeout(sem, timeout); - raw_spin_unlock_irqrestore(&sem->lock, flags); + raw_spin_unlock_irq(&sem->lock); return result; }