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    SubjectRe: [RFC PATCH 1/8] rqbased-dm: allow blk_get_request() to be called from interrupt context
    On Wed, Dec 20 2006, Chen, Kenneth W wrote:
    > Kiyoshi Ueda wrote on Wednesday, December 20, 2006 9:50 AM
    > > On Wed, 20 Dec 2006 14:48:49 +0100, Jens Axboe <jens.axboe@oracle.com> wrote:
    > > > Big NACK on this - it's not only really ugly, it's also buggy to pass
    > > > interrupt flags as function arguments. As you also mention in the 0/1
    > > > mail, this also breaks CFQ.
    > > >
    > > > Why do you need in-interrupt request allocation?
    > >
    > > Because I'd like to use blk_get_request() in q->request_fn()
    > > which can be called from interrupt context like below:
    > > scsi_io_completion -> scsi_end_request -> scsi_next_command
    > > -> scsi_run_queue -> blk_run_queue -> q->request_fn
    > >
    > > [ ...]
    > >
    > > Do you think creating another function like blk_get_request_nowait()
    > > is acceptable?
    >
    > You don't need to create another function. blk_get_request already
    > have both wait and nowait semantics via gfp_mask argument. If you can
    > not block, then clear __GFP_WAIT bit in the mask before calling
    > blk_get_request.

    Doesn't work, get_request() assumes that the caller grabbed the queue
    lock and disabled interrupts, and does an unconditionaly

    spin_unlock_irq()

    inside it. So you can NEVER use get_request() for even GFP_ATOMIC
    allocations, as it assumes the original context was a process context.

    --
    Jens Axboe

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