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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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