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    SubjectRe: block: avoid unconditionally freeing previously allocated request_queue
    On Tue, May 25 2010 at 10:37pm -0400,
    Kiyoshi Ueda <k-ueda@ct.jp.nec.com> wrote:

    > Hi Mike,
    >
    > On 05/26/2010 01:34 AM +0900, Mike Snitzer wrote:
    > > Mike Snitzer <snitzer@redhat.com> wrote:
    > >> Kiyoshi Ueda <k-ueda@ct.jp.nec.com> wrote:
    > >>>> +/*
    > >>>> + * Fully initialize a request-based queue (->elevator, ->request_fn, etc).
    > >>>> + */
    > >>>> +static int dm_init_request_based_queue(struct mapped_device *md)
    > >>>> +{
    > >>>> + struct request_queue *q = NULL;
    > >>>> +
    > >>>> + /* Avoid re-initializing the queue if already fully initialized */
    > >>>> + if (!md->queue->elevator) {
    > >>>> + /* Fully initialize the queue */
    > >>>> + q = blk_init_allocated_queue(md->queue, dm_request_fn, NULL);
    > >>>> + if (!q)
    > >>>> + return 0;
    > >>>
    > >>> When blk_init_allocated_queue() fails, the block-layer seems not to
    > >>> guarantee that the queue is still available.
    > >>
    > >> Ouch, yes this portion of blk_init_allocated_queue_node() is certainly
    > >> problematic:
    > >>
    > >> if (blk_init_free_list(q)) {
    > >> kmem_cache_free(blk_requestq_cachep, q);
    > >> return NULL;
    > >> }
    >
    > Not only that. The blk_put_queue() in blk_init_allocated_queue_node()
    > will also free the queue:
    >
    > if (!elevator_init(q, NULL)) {
    > blk_queue_congestion_threshold(q);
    > return q;
    > }
    >
    > blk_put_queue(q);
    > return NULL;

    OK, I'll post v2 that addresses this and we'll see what Jens says.

    Mike


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