On Wed, Mar 26, 2008 at 01:29:58PM -0700, Luck, Tony wrote:
I did brifly consider creating a spinaphore data type, but it's
significantly less code to create down_spin().
Thanks for testing and putting this together in patch form. I've fixed it
up to address Jens' astute comment and added it to my semaphore patchset.
http://git.kernel.org/?p=linux/kernel/git/willy/misc.git;a=shortlog;h=semaphore-200803...
Stephen, I've updated the 'semaphore' tag to point ot the same place as
semaphore-20080327, so please change your linux-next tree from pulling
semaphore-20080314 to just pulling plain 'semaphore'. I'll use this
method of tagging from now on.
Here's the edited patch.
commit 517df6fedc88af3f871cf827a62ef1a1a2073645
Author: Matthew Wilcox <matthew@wil.cx>
Date: Thu Mar 27 09:49:26 2008 -0400
Add down_spin()
ia64 would like to use a semaphore in flush_tlb_all() as it can have
multiple tokens. Unfortunately, it's currently nested inside a spinlock,
so they can't sleep. down_spin() is the cheapest solution to implement.
Signed-off-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
diff --git a/include/linux/semaphore.h b/include/linux/semaphore.h
index a7125da..13b5f32 100644
--- a/include/linux/semaphore.h
+++ b/include/linux/semaphore.h
@@ -78,6 +78,14 @@ extern int __must_check down_trylock(struct semaphore *sem);
extern int __must_check down_timeout(struct semaphore *sem, long jiffies);
/*
+ * As down(), except this function will spin waiting for the semaphore
+ * instead of sleeping. It is safe to use while holding a spinlock or
+ * with interrupts disabled. It should not be called from interrupt
+ * context as this may lead to deadlocks.
+ */
+extern void down_spin(struct semaphore *sem);
+
+/*
* Release the semaphore. Unlike mutexes, up() may be called from any
* context and even by tasks which have never called down().
*/
diff --git a/kernel/semaphore.c b/kernel/semaphore.c
index bef977b..a242d87 100644
--- a/kernel/semaphore.c
+++ b/kernel/semaphore.c
@@ -26,6 +26,7 @@ static noinline void __down(struct semaphore *sem);
static noinline int __down_interruptible(struct semaphore *sem);
static noinline int __down_killable(struct semaphore *sem);
static noinline int __down_timeout(struct semaphore *sem, long jiffies);
+static noinline void __down_spin(struct semaphore *sem, unsigned long flags);
static noinline void __up(struct semaphore *sem);
void down(struct semaphore *sem)
@@ -117,6 +118,20 @@ int down_timeout(struct semaphore *sem, long jiffies)
}
EXPORT_SYMBOL(down_timeout);
+void down_spin(struct semaphore *sem)
+{
+ unsigned long flags;
+
+ spin_lock_irqsave(&sem->lock, flags);
+ if (likely(sem->count > 0)) {
+ sem->count--;
+ spin_unlock_irqrestore(&sem->lock, flags);
+ } else {
+ __down_spin(sem, flags);
+ }
+}
+EXPORT_SYMBOL(down_spin);
+
void up(struct semaphore *sem)
{
unsigned long flags;
@@ -197,6 +212,20 @@ static noinline int __sched __down_timeout(struct semaphore
return __down_common(sem, TASK_UNINTERRUPTIBLE, jiffies);
}
+static noinline void __sched __down_spin(struct semaphore *sem,
+ unsigned long flags)
+{
+ struct semaphore_waiter waiter;
+
+ list_add_tail(&waiter.list, &sem->wait_list);
+ waiter.task = current;
+ waiter.up = 0;
+
+ spin_unlock_irqrestore(&sem->lock, flags);
+ while (!waiter.up)
+ cpu_relax();
+}
+
static noinline void __sched __up(struct semaphore *sem)
{
struct semaphore_waiter *waiter = list_first_entry(&sem->wait_list,
--
Intel are signing my paycheques ... these opinions are still mine
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours. We can't possibly take such
a retrograde step."
--
