Re: AS spin lock bugs

[Nick Piggin]

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.

Maybe I'm wrong, did you actually see misbehaviour?


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