From b093ab3f1967a9d777f009a623f778899784214d Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Sat, 10 May 2008 20:43:22 -0700 Subject: [PATCH] Revert "semaphore: fix" This reverts commit d54d3610453479f1270325ec3fe94a94e6ba738c, as it has been reported to cause a regression with processes stuck in __down(), apparently because some missing wakeup. Quoth Sven Wegener: "I'm currently investigating a regression that has showed up with my last git pull yesterday. Bisecting the commits showed bf726e "semaphore: fix" to be the culprit, reverting it fixed the issue. Symptoms: During heavy filesystem usage (e.g. a kernel compile) I get several compiler processes in uninterruptible sleep, blocking all i/o on the filesystem. System is an Intel Core 2 Quad running a 64bit kernel and userspace. Filesystem is xfs on top of lvm. See below for the output of sysrq-w." See http://lkml.org/lkml/2008/5/10/45 for full report. In the meantime, we can just fix the BKL performance regression by reverting back to the good old BKL spinlock implementation instead, since any sleeping lock will generally perform badly, especially if it tries to be fair. Reported-by: Sven Wegener Cc: Andrew Morton Cc: Ingo Molnar Signed-off-by: Linus Torvalds --- kernel/semaphore.c | 64 ++++++++++++++++++++++++---------------------- 1 file changed, 34 insertions(+), 30 deletions(-) diff --git a/kernel/semaphore.c b/kernel/semaphore.c index 5e41217239e89..5c2942e768cdd 100644 --- a/kernel/semaphore.c +++ b/kernel/semaphore.c @@ -54,9 +54,10 @@ void down(struct semaphore *sem) unsigned long flags; spin_lock_irqsave(&sem->lock, flags); - if (unlikely(!sem->count)) + if (likely(sem->count > 0)) + sem->count--; + else __down(sem); - sem->count--; spin_unlock_irqrestore(&sem->lock, flags); } EXPORT_SYMBOL(down); @@ -76,10 +77,10 @@ int down_interruptible(struct semaphore *sem) int result = 0; spin_lock_irqsave(&sem->lock, flags); - if (unlikely(!sem->count)) - result = __down_interruptible(sem); - if (!result) + if (likely(sem->count > 0)) sem->count--; + else + result = __down_interruptible(sem); spin_unlock_irqrestore(&sem->lock, flags); return result; @@ -102,10 +103,10 @@ int down_killable(struct semaphore *sem) int result = 0; spin_lock_irqsave(&sem->lock, flags); - if (unlikely(!sem->count)) - result = __down_killable(sem); - if (!result) + if (likely(sem->count > 0)) sem->count--; + else + result = __down_killable(sem); spin_unlock_irqrestore(&sem->lock, flags); return result; @@ -156,10 +157,10 @@ int down_timeout(struct semaphore *sem, long jiffies) int result = 0; spin_lock_irqsave(&sem->lock, flags); - if (unlikely(!sem->count)) - result = __down_timeout(sem, jiffies); - if (!result) + if (likely(sem->count > 0)) sem->count--; + else + result = __down_timeout(sem, jiffies); spin_unlock_irqrestore(&sem->lock, flags); return result; @@ -178,8 +179,9 @@ void up(struct semaphore *sem) unsigned long flags; spin_lock_irqsave(&sem->lock, flags); - sem->count++; - if (unlikely(!list_empty(&sem->wait_list))) + if (likely(list_empty(&sem->wait_list))) + sem->count++; + else __up(sem); spin_unlock_irqrestore(&sem->lock, flags); } @@ -190,6 +192,7 @@ EXPORT_SYMBOL(up); struct semaphore_waiter { struct list_head list; struct task_struct *task; + int up; }; /* @@ -202,34 +205,33 @@ static inline int __sched __down_common(struct semaphore *sem, long state, { struct task_struct *task = current; struct semaphore_waiter waiter; - int ret = 0; - waiter.task = task; list_add_tail(&waiter.list, &sem->wait_list); + waiter.task = task; + waiter.up = 0; for (;;) { - if (state == TASK_INTERRUPTIBLE && signal_pending(task)) { - ret = -EINTR; - break; - } - if (state == TASK_KILLABLE && fatal_signal_pending(task)) { - ret = -EINTR; - break; - } - if (timeout <= 0) { - ret = -ETIME; - break; - } + if (state == TASK_INTERRUPTIBLE && signal_pending(task)) + goto interrupted; + if (state == TASK_KILLABLE && fatal_signal_pending(task)) + goto interrupted; + if (timeout <= 0) + goto timed_out; __set_task_state(task, state); spin_unlock_irq(&sem->lock); timeout = schedule_timeout(timeout); spin_lock_irq(&sem->lock); - if (sem->count > 0) - break; + if (waiter.up) + return 0; } + timed_out: + list_del(&waiter.list); + return -ETIME; + + interrupted: list_del(&waiter.list); - return ret; + return -EINTR; } static noinline void __sched __down(struct semaphore *sem) @@ -256,5 +258,7 @@ static noinline void __sched __up(struct semaphore *sem) { struct semaphore_waiter *waiter = list_first_entry(&sem->wait_list, struct semaphore_waiter, list); + list_del(&waiter->list); + waiter->up = 1; wake_up_process(waiter->task); } -- 2.39.5