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SubjectRe: [PATCH 2/6] block: allow blk_execute_rq_nowait() to be called from IRQ context
On 2011-10-26 03:02, Tejun Heo wrote:
> Currently blk_execute_rq_nowait() directly calls __blk_run_queue() and
> thus must be called from sleepable context. This patch updates the
> function such that it can be called from non-sleepable context and
> schedules async execution in such cases. This will be used to
> unexport elv_add_request().
>
> While at it, add FIXME comment for REQ_TYPE_PM_RESUME special case.
>
> -v2: hch pointed out that blk_execute_rq_nowait() can be hot path for
> some drivers. Retained direct execution from sleepable context.

Ugh, this looks nasty:

> + bool may_sleep = !preempt_count() && !irqs_disabled();

please don't ever do that. Pass the context in instead.

> + /*
> + * Some drivers beat this path pretty hard. As an optimization, if
> + * we're being called from sleepable context, run @q directly.
> + */
> + if (may_sleep) {
> + __blk_run_queue(q);
> + /*
> + * The queue is stopped so it won't be run.
> + * FIXME: Please kill me along with REQ_TYPE_PM_RESUME.
> + */
> + if (rq->cmd_type == REQ_TYPE_PM_RESUME)
> + q->request_fn(q);

This is very nasty as well.

--
Jens Axboe



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