On 10/10/2010 09:16 PM, Andi Kleen wrote:
>> Not if in_interrupt is set though?
>> + if (per_cpu(io_wq_cpu, cpu) == current && !in_interrupt()) {
>>
>> What I am missing here?
>
> The interrupt doesn't block on the task.
>
> Actually most likely that check isn't needed anyways because
> that should not happen, was just pure paranoia from my side.
I don't think so. If you run crypto in async mode, you get asynchronous
callback (kcryptd_asynnc_done() here).
AFAIK this callback is called in interrupt context. This callback
decreases pending counter and if it reach zero it calls
kcryptd_crypt_write_io_submit() -> kcryptd_queue_io().
You cannot call direct encryption if it is called from async callback,
so the IO must be always queued to IO workqueue for later.
So the in_interrupt() is IMHO equivalent of async flag and it is
properly placed there.
But previously, there were threads per device, so if one IO thread blocks,
others stacked mappings can continue
Now I see possibility for deadlock there because we have one io thread now
(assuming that 1 CPU situation Alasdair mentioned).
Or is there a mistake in my analysis?
>
>>
>> (And assume there is only 1 CPU too for worst case behaviour, presumably.)
>
> One per process, previously it was always one per CPU.
Nope, one singlethread per crypt device (resp. two: io + crypt).
Milan
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