Messages in this thread Patch in this message | | | Date | Thu, 13 Aug 2009 21:52:32 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: [GIT pull] genirq fixes for 2.6.31 |
| |
On Thu, 13 Aug 2009, Linus Torvalds wrote: > Now, I can see a bug, which is that "action->tsk" may have been set to > NULL. But I can't see a race, and I can't see a reason for all the code > movement. So quite frankly, I think the comments (both in the code and in > the commit message) are just wrong. And the odd "load it first, then do > other things" code looks confused. > > So why is this not just a > > if (action->thread) > wake_up_process(action->thread); > > with appropriate comments?
What guarantees that the compiler does not dereference action->thread twice and the action->thread = NULL; operation happens between the check and the wake_up_process() call? I might be paranoid, but ...
> Or, alternatively, just move all the "clear action->thread" in free_irq() > to after having done the "synchronize_irq()" thing, and then - afaik - > you'll not need that test at all, because you're guaranteed that as long > as you're in an interrupt handler, the thing shouldn't be cleared.
Right, I looked at that as well, but we need to do it different than just calling synchronize_irq(), as we need to keep desc->lock after we established that no interrupt is in progress. Otherwise we can run into the same problem which we have right now. Patch below.
Thanks,
tglx --- diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c index 76e109a..06fa022 100644 --- a/kernel/irq/manage.c +++ b/kernel/irq/manage.c @@ -895,7 +907,28 @@ static struct irqaction *__free_irq(unsigned int irq, void *dev_id) if (!desc) return NULL; - atomic_spin_lock_irqsave(&desc->lock, flags); + while (1) { + /* + * Wait until we're out of the critical section. This might + * give the wrong answer due to the lack of memory barriers. + */ + while (desc->status & IRQ_INPROGRESS) + cpu_relax(); + + /* + * Check under the lock again. If irq is not in + * progress we keep the lock held until we removed + * action. We do not care about an already running irq + * thread here. We care about it when we stop the thread. + */ + atomic_spin_lock_irqsave(&desc->lock, flags); + + if (!(desc->status & IRQ_INPROGRESS)) + break; + + /* Try again */ + atomic_spin_unlock_irqrestore(&desc->lock, flags); + } /* * There can be multiple actions per IRQ descriptor, find the right
| |