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Date: Wed, 19 Oct 2011 11:22:03 -0400
From: Vivek Goyal <vgoyal@...hat.com>
To: Tejun Heo <tj@...nel.org>
Cc: axboe@...nel.dk, linux-kernel@...r.kernel.org, ctalbott@...gle.com
Subject: Re: [PATCH 08/10] block: make get_request[_wait]() fail if queue is
dead
On Tue, Oct 18, 2011 at 09:26:22PM -0700, Tejun Heo wrote:
> Currently get_request[_wait]() allocates request whether queue is dead
> or not. This patch makes get_request[_wait]() return NULL if @q is
> dead. blk_queue_bio() is updated to fail the submitted bio if request
> allocation fails. While at it, add docbook comments for
> get_request[_wait]().
>
> Note that the current code has rather unclear (there are spurious DEAD
> tests scattered around) assumption that the owner of a queue
> guarantees that no request travels block layer if the queue is dead
> and this patch in itself doesn't change much; however, this will allow
> fixing the broken assumption in the next patch.
Ok, so this patch will now make sure that __make_request() will return
error if queue is dead. So previous blk_throtl_bio() change is fine.
Thanks
Vivek
>
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Cc: Jens Axboe <axboe@...nel.dk>
> ---
> block/blk-core.c | 54 ++++++++++++++++++++++++++++++++++++++----------------
> 1 files changed, 38 insertions(+), 16 deletions(-)
>
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 7a90317..fc10f53 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -710,10 +710,19 @@ static bool blk_rq_should_init_elevator(struct bio *bio)
> return true;
> }
>
> -/*
> - * Get a free request, queue_lock must be held.
> - * Returns NULL on failure, with queue_lock held.
> - * Returns !NULL on success, with queue_lock *not held*.
> +/**
> + * get_request - get a free request
> + * @q: request_queue to allocate request from
> + * @rw_flags: RW and SYNC flags
> + * @bio: bio to allocate request for (can be %NULL)
> + * @gfp_mask: allocation mask
> + *
> + * Get a free request from @q. This function may fail under memory
> + * pressure or if @q is dead.
> + *
> + * Must be callled with @q->queue_lock held and,
> + * Returns %NULL on failure, with @q->queue_lock held.
> + * Returns !%NULL on success, with @q->queue_lock *not held*.
> */
> static struct request *get_request(struct request_queue *q, int rw_flags,
> struct bio *bio, gfp_t gfp_mask)
> @@ -724,6 +733,9 @@ static struct request *get_request(struct request_queue *q, int rw_flags,
> const bool is_sync = rw_is_sync(rw_flags) != 0;
> int may_queue;
>
> + if (unlikely(test_bit(QUEUE_FLAG_DEAD, &q->queue_flags)))
> + return NULL;
> +
> may_queue = elv_may_queue(q, rw_flags);
> if (may_queue == ELV_MQUEUE_NO)
> goto rq_starved;
> @@ -816,11 +828,18 @@ out:
> return rq;
> }
>
> -/*
> - * No available requests for this queue, wait for some requests to become
> - * available.
> +/**
> + * get_request_wait - get a free request with retry
> + * @q: request_queue to allocate request from
> + * @rw_flags: RW and SYNC flags
> + * @bio: bio to allocate request for (can be %NULL)
> *
> - * Called with q->queue_lock held, and returns with it unlocked.
> + * Get a free request from @q. This function keeps retrying under memory
> + * pressure and fails iff @q is dead.
> + *
> + * Must be callled with @q->queue_lock held and,
> + * Returns %NULL on failure, with @q->queue_lock held.
> + * Returns !%NULL on success, with @q->queue_lock *not held*.
> */
> static struct request *get_request_wait(struct request_queue *q, int rw_flags,
> struct bio *bio)
> @@ -834,6 +853,9 @@ static struct request *get_request_wait(struct request_queue *q, int rw_flags,
> struct io_context *ioc;
> struct request_list *rl = &q->rq;
>
> + if (unlikely(test_bit(QUEUE_FLAG_DEAD, &q->queue_flags)))
> + return NULL;
> +
> prepare_to_wait_exclusive(&rl->wait[is_sync], &wait,
> TASK_UNINTERRUPTIBLE);
>
> @@ -864,19 +886,15 @@ struct request *blk_get_request(struct request_queue *q, int rw, gfp_t gfp_mask)
> {
> struct request *rq;
>
> - if (unlikely(test_bit(QUEUE_FLAG_DEAD, &q->queue_flags)))
> - return NULL;
> -
> BUG_ON(rw != READ && rw != WRITE);
>
> spin_lock_irq(q->queue_lock);
> - if (gfp_mask & __GFP_WAIT) {
> + if (gfp_mask & __GFP_WAIT)
> rq = get_request_wait(q, rw, NULL);
> - } else {
> + else
> rq = get_request(q, rw, NULL, gfp_mask);
> - if (!rq)
> - spin_unlock_irq(q->queue_lock);
> - }
> + if (!rq)
> + spin_unlock_irq(q->queue_lock);
> /* q->queue_lock is unlocked at this point */
>
> return rq;
> @@ -1300,6 +1318,10 @@ get_rq:
> * Returns with the queue unlocked.
> */
> req = get_request_wait(q, rw_flags, bio);
> + if (unlikely(!req)) {
> + bio_endio(bio, -ENODEV); /* @q is dead */
> + goto out_unlock;
> + }
>
> /*
> * After dropping the lock and possibly sleeping here, our request
> --
> 1.7.3.1
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