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    SubjectRe: [PATCH v3] blk: fix a wrong accounting of hd_struct->in_flight
    On 2010-10-15 10:39, Yasuaki Ishimatsu wrote:
    > Hi Jens,
    >
    > Jens Axboe wrote:
    >> On 2010-10-14 14:48, Yasuaki Ishimatsu wrote:
    >>> Index: linux-2.6.36-rc7/block/blk-core.c
    >>> ===================================================================
    >>> --- linux-2.6.36-rc7.orig/block/blk-core.c 2010-10-07 05:39:52.000000000 +0900
    >>> +++ linux-2.6.36-rc7/block/blk-core.c 2010-10-14 17:25:43.000000000 +0900
    >>> @@ -66,9 +66,15 @@ static void drive_stat_acct(struct reque
    >>> cpu = part_stat_lock();
    >>> part = disk_map_sector_rcu(rq->rq_disk, blk_rq_pos(rq));
    >>>
    >>> - if (!new_io)
    >>> + if (!new_io) {
    >>> + if (unlikely(rq->part != part)) {
    >>> + part_dec_in_flight(rq->part, rw);
    >>> + part_inc_in_flight(part, rw);
    >>> + rq->part = part;
    >>> + }
    >>> part_stat_inc(cpu, part, merges[rw]);
    >>> - else {
    >>> + } else {
    >>> + rq->part = part;
    >>> part_round_stats(cpu, part);
    >>> part_inc_in_flight(part, rw);
    >>> }
    >>
    >> I was thinking that we'd do away with the lookup always if ->part was
    >> already set. It will probably require a quiscing of IO on partition
    >> table reload, though.
    >
    > O.K.
    > I removed extra part lookups. Following patch also fixed a wrong accounting of
    > hd_struct->in_flight. But I could not invent how to stop IOs when
    > reloading partition table. Do you have some idea?

    This looks good! To quiesce the queue, something like the below.
    Completely untested.

    diff --git a/block/blk-core.c b/block/blk-core.c
    index 32a1c12..dce2f68 100644
    --- a/block/blk-core.c
    +++ b/block/blk-core.c
    @@ -796,11 +796,16 @@ static struct request *get_request(struct request_queue *q, int rw_flags,
    rl->starved[is_sync] = 0;

    priv = !test_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
    - if (priv)
    + if (priv) {
    rl->elvpriv++;

    - if (blk_queue_io_stat(q))
    - rw_flags |= REQ_IO_STAT;
    + /*
    + * Don't do stats for non-priv requests
    + */
    + if (blk_queue_io_stat(q))
    + rw_flags |= REQ_IO_STAT;
    + }
    +
    spin_unlock_irq(q->queue_lock);

    rq = blk_alloc_request(q, rw_flags, priv, gfp_mask);
    diff --git a/block/genhd.c b/block/genhd.c
    index 59a2db6..2ecbe7d 100644
    --- a/block/genhd.c
    +++ b/block/genhd.c
    @@ -925,8 +925,10 @@ static void disk_free_ptbl_rcu_cb(struct rcu_head *head)
    {
    struct disk_part_tbl *ptbl =
    container_of(head, struct disk_part_tbl, rcu_head);
    + struct gendisk *disk = ptbl->disk;

    kfree(ptbl);
    + elv_quiesce_end(disk->queue);
    }

    /**
    @@ -949,6 +951,7 @@ static void disk_replace_part_tbl(struct gendisk *disk,

    if (old_ptbl) {
    rcu_assign_pointer(old_ptbl->last_lookup, NULL);
    + elv_quiesce_start(disk->queue);
    call_rcu(&old_ptbl->rcu_head, disk_free_ptbl_rcu_cb);
    }
    }
    diff --git a/include/linux/genhd.h b/include/linux/genhd.h
    index 5f2f4c4..69b21bb 100644
    --- a/include/linux/genhd.h
    +++ b/include/linux/genhd.h
    @@ -130,6 +130,7 @@ struct disk_part_tbl {
    struct rcu_head rcu_head;
    int len;
    struct hd_struct *last_lookup;
    + struct gendisk *disk;
    struct hd_struct *part[];
    };

    --
    Jens Axboe



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