Messages in this thread | | | Date | Thu, 13 Nov 2003 11:59:01 +0100 | From | Jens Axboe <> | Subject | Re: AS spin lock bugs |
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On Thu, Nov 13 2003, Nick Piggin wrote: > > > Jens Axboe wrote: > > >Hi, > > > >Was looking at io tracking for cfq, and I think I found some spin lock > >bugs in current as (current BK). as_update_iohist() runs from > >add_request which is typically in process context. It could be run with > >interrupts disabled though, either driver private stuff or using the > >generic block layer tagging. > > > >Anyways, as_update_iohist() grabs aic->lock without disabling > >interrupts, while as_completed_request() typically runs at interrupt > >time and grabs the same lock. Deadlock. > > > >To be safe, both need to use the flags saving lock variants. > > > > Hi Jens, > I was hoping everything ran under the queue lock which should always > have interrupts off on the local CPU. The lock in question is to prevent > a as_completed_request on one queue from racing with as_update_iohist > on another. Each would be on a different CPU.
Ah yes you are right. The queue lock will be held in both places.
> Maybe I'm wrong, did you actually see misbehaviour?
Nope, just looking over the code. What about the second lock, why is that needed? I don't see that protecting anything.
-- Jens Axboe
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