Messages in this thread | | | Date | Tue, 13 Oct 2009 13:34:19 -0700 | From | Andrew Morton <> | Subject | Re: [Patch v4] rwsem: fix rwsem_is_locked() bugs |
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On Thu, 8 Oct 2009 05:23:53 -0400 Amerigo Wang <amwang@redhat.com> 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.
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