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    Subject[PATCH 2.6.23-rc7 3/3] raid5: fix ops_complete_biofill
    Date
    ops_complete_biofill tried to avoid calling handle_stripe since all the
    state necessary to return read completions is available. However the
    process of determining whether more read requests are pending requires
    locking the stripe (to block add_stripe_bio from updating dev->toead).
    ops_complete_biofill can run in tasklet context, so rather than upgrading
    all the stripe locks from spin_lock to spin_lock_bh this patch just moves
    read completion handling back into handle_stripe.

    Found-by: Yuri Tikhonov <yur@emcraft.com>
    Signed-off-by: Dan Williams <dan.j.williams@intel.com>
    ---

    drivers/md/raid5.c | 90 +++++++++++++++++++++++++++-------------------------
    1 files changed, 46 insertions(+), 44 deletions(-)

    diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
    index 4d63773..38c8893 100644
    --- a/drivers/md/raid5.c
    +++ b/drivers/md/raid5.c
    @@ -512,54 +512,12 @@ async_copy_data(int frombio, struct bio *bio, struct page *page,
    static void ops_complete_biofill(void *stripe_head_ref)
    {
    struct stripe_head *sh = stripe_head_ref;
    - struct bio *return_bi = NULL;
    - raid5_conf_t *conf = sh->raid_conf;
    - int i, more_to_read = 0;

    pr_debug("%s: stripe %llu\n", __FUNCTION__,
    (unsigned long long)sh->sector);

    - /* clear completed biofills */
    - for (i = sh->disks; i--; ) {
    - struct r5dev *dev = &sh->dev[i];
    - /* check if this stripe has new incoming reads */
    - if (dev->toread)
    - more_to_read++;
    -
    - /* acknowledge completion of a biofill operation */
    - /* and check if we need to reply to a read request
    - */
    - if (test_bit(R5_Wantfill, &dev->flags) && !dev->toread) {
    - struct bio *rbi, *rbi2;
    - clear_bit(R5_Wantfill, &dev->flags);
    -
    - /* The access to dev->read is outside of the
    - * spin_lock_irq(&conf->device_lock), but is protected
    - * by the STRIPE_OP_BIOFILL pending bit
    - */
    - BUG_ON(!dev->read);
    - rbi = dev->read;
    - dev->read = NULL;
    - while (rbi && rbi->bi_sector <
    - dev->sector + STRIPE_SECTORS) {
    - rbi2 = r5_next_bio(rbi, dev->sector);
    - spin_lock_irq(&conf->device_lock);
    - if (--rbi->bi_phys_segments == 0) {
    - rbi->bi_next = return_bi;
    - return_bi = rbi;
    - }
    - spin_unlock_irq(&conf->device_lock);
    - rbi = rbi2;
    - }
    - }
    - }
    - clear_bit(STRIPE_OP_BIOFILL, &sh->ops.ack);
    - clear_bit(STRIPE_OP_BIOFILL, &sh->ops.pending);
    -
    - return_io(return_bi);
    -
    - if (more_to_read)
    - set_bit(STRIPE_HANDLE, &sh->state);
    + set_bit(STRIPE_OP_BIOFILL, &sh->ops.complete);
    + set_bit(STRIPE_HANDLE, &sh->state);
    release_stripe(sh);
    }

    @@ -2112,6 +2070,42 @@ static void handle_issuing_new_read_requests6(struct stripe_head *sh,
    }


    +/* handle_completed_read_requests - return completion for reads and allow
    + * new read operations to be submitted to the stripe.
    + */
    +static void handle_completed_read_requests(raid5_conf_t *conf,
    + struct stripe_head *sh,
    + struct bio **return_bi)
    +{
    + int i;
    +
    + pr_debug("%s: stripe %llu\n", __FUNCTION__,
    + (unsigned long long)sh->sector);
    +
    + /* check if we need to reply to a read request */
    + for (i = sh->disks; i--; ) {
    + struct r5dev *dev = &sh->dev[i];
    +
    + if (test_and_clear_bit(R5_Wantfill, &dev->flags)) {
    + struct bio *rbi, *rbi2;
    +
    + rbi = dev->read;
    + dev->read = NULL;
    + while (rbi && rbi->bi_sector <
    + dev->sector + STRIPE_SECTORS) {
    + rbi2 = r5_next_bio(rbi, dev->sector);
    + spin_lock_irq(&conf->device_lock);
    + if (--rbi->bi_phys_segments == 0) {
    + rbi->bi_next = *return_bi;
    + *return_bi = rbi;
    + }
    + spin_unlock_irq(&conf->device_lock);
    + rbi = rbi2;
    + }
    + }
    + }
    +}
    +
    /* handle_completed_write_requests
    * any written block on an uptodate or failed drive can be returned.
    * Note that if we 'wrote' to a failed drive, it will be UPTODATE, but
    @@ -2633,6 +2627,14 @@ static void handle_stripe5(struct stripe_head *sh)
    s.expanded = test_bit(STRIPE_EXPAND_READY, &sh->state);
    /* Now to look around and see what can be done */

    + if (test_bit(STRIPE_OP_BIOFILL, &sh->ops.complete)) {
    + clear_bit(STRIPE_OP_BIOFILL, &sh->ops.ack);
    + clear_bit(STRIPE_OP_BIOFILL, &sh->ops.pending);
    + clear_bit(STRIPE_OP_BIOFILL, &sh->ops.complete);
    +
    + handle_completed_read_requests(conf, sh, &return_bi);
    + }
    +
    rcu_read_lock();
    for (i=disks; i--; ) {
    mdk_rdev_t *rdev;
    -
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