On Thu, 8 Oct 2009 05:23:53 -0400
Amerigo Wang <amwang@xxxxxxxxxx> wrote:
--- a/include/linux/rwsem-spinlock.h
+++ b/include/linux/rwsem-spinlock.h
@@ -71,7 +71,13 @@ extern void __downgrade_write(struct rw_semaphore *sem);
static inline int rwsem_is_locked(struct rw_semaphore *sem)
{
- return (sem->activity != 0);
+ int ret = 1;
+
+ if (spin_trylock_irq(&sem->wait_lock)) {
+ ret = (sem->activity != 0);
+ spin_unlock_irq(&sem->wait_lock);
+ }
+ return ret;
}
a) probably to large to be inlined
b) the function will now cause bugs if called under
local_irq_disable(). That wasn't the case before. Fixable via
spin_lock_irqsave().
In the present kernel there don't appear to be any irqs-off callers. There may of course be some out-of-tree ones which will get bitten by
this semantic change.
If we decide to leave this new rule in place then we should add a
WARN_ON(irqs_disabled()) to prevent hitting people with a nasty, subtle
bug.
Methinks that _irqsave() is better.