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    SubjectRe: [PATCH 2/2] block: fix accounting bug on cross partition merges
    On 01/05/2011 03:00 PM, Jens Axboe wrote:
    > On 2011-01-04 16:55, Jerome Marchand wrote:
    >> + } else {
    >> + part = disk_map_sector_rcu(rq->rq_disk, blk_rq_pos(rq));
    >> + if (!kref_test_and_get(&part->ref)) {
    >> + /*
    >> + * The partition is already being removed,
    >> + * the request will be accounted on the disk only
    >> + *
    >> + * We take a reference on disk->part0 although that
    >> + * partition will never be deleted, so we can treat
    >> + * it as any other partition.
    >> + */
    >> + part = &rq->rq_disk->part0;
    >> + kref_get(&part->ref);
    >> + }
    >
    > This still doesn't work. So you are inside the if {} block, you know
    > what someone has dropped the last reference and the call_rcu() is being
    > scheduled. Adding a reference now will not prevent 'part' from going
    > away as soon as you do part_stat_unlock().

    And what is the problem with that since we don't use 'part' (as returned
    by disk_map_sector_rcu()), but disk->part0 instead?

    > As per my last email, you
    > need a check in the rcu callback to ensure that the ref is 0.
    >
    >



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