Messages in this thread | ![/](/images/icornerl.gif) | | Date | Wed, 20 Dec 2006 20:17:33 +0100 | From | Jens Axboe <> | Subject | Re: [RFC PATCH 1/8] rqbased-dm: allow blk_get_request() to be called from interrupt context |
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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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