[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v3 18/18] xen/arm: IRQ: Handle multiple action per IRQ
On 04/17/2014 08:07 AM, Jan Beulich wrote: >>>> On 16.04.14 at 18:23, <julien.grall@xxxxxxxxxx> wrote: >> On 04/16/2014 05:17 PM, Ian Campbell wrote: >>> On Wed, 2014-04-16 at 17:06 +0100, Julien Grall wrote: >>>> On 04/16/2014 04:54 PM, Ian Campbell wrote: >>>>> On Tue, 2014-04-08 at 15:44 +0100, Julien Grall wrote: >>>>>> desc->status &= ~IRQ_PENDING; >>>>>> spin_unlock_irq(&desc->lock); >>>>>> - action->handler(irq, action->dev_id, regs); >>>>>> + list_for_each_entry_safe(action, next, &desc->action, next) >>>>>> + action->handler(irq, action->dev_id, regs); >>>>> >>>>> You aren't removing entries from within the loop so I don't think you >>>>> need the _safe variant. >>>> >>>> As we release the desc->lock here, it might be possible to have the list >>>> changed under the CPU feet by release_irq. >>>> >>>> With the double-linked list, how do we make sure that it won't happen? >>> >>> Normally by using a lock. I don't know if even list_for_each_entry_safe >>> is safe against concurrent changes to the list from other threads, I >>> think it only refers to safe to changing the list within the loop in >>> this thread. >>> >> >> Hmmmm... I'm wondering if we can keep desc->lock held while calling the >> action handler and enable IRQ. > > That would set you up for problems with the handler wanting to > manipulate its IRQ (which might imply locking desc). I'd suggest > looking at how Linux deals with this (synchronize_irq() in particular). The release_irq code is borrowed from Linux. We already synchronize at the end. We have to delete the element in the critical section to avoid race with adding a new element. synchronizing in the critical section is not possible because do_IRQ will have to take the lock to clear the IRQ_INPROGRESS flag. In Linux case, they are safe because they are using a single linked list. -- Julien Grall _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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