Messages in this thread Patch in this message | | | Date | Thu, 13 Aug 2009 21:59:34 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: [GIT pull] genirq fixes for 2.6.31 |
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Sorry, sent out the wrong patch :(
On Thu, 13 Aug 2009, Thomas Gleixner wrote:
> 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
--- 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; - 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. + */ + spin_lock_irqsave(&desc->lock, flags); + + if (!(desc->status & IRQ_INPROGRESS)) + break; + + /* Try again */ + spin_unlock_irqrestore(&desc->lock, flags); + } /* * There can be multiple actions per IRQ descriptor, find the right
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