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    Subject[patch 017/101] Fix various bugs with aligned reads in RAID5.
    From: Neil Brown <neilb@suse.de>

    Fix various bugs with aligned reads in RAID5.

    It is possible for raid5 to be sent a bio that is too big
    for an underlying device. So if it is a READ that we
    pass stright down to a device, it will fail and confuse
    RAID5.

    So in 'chunk_aligned_read' we check that the bio fits within the
    parameters for the target device and if it doesn't fit, fall back
    on reading through the stripe cache and making lots of one-page
    requests.

    Note that this is the earliest time we can check against the device
    because earlier we don't have a lock on the device, so it could change
    underneath us.

    Also, the code for handling a retry through the cache when a read
    fails has not been tested and was badly broken. This patch fixes that
    code.

    Signed-off-by: Neil Brown <neilb@suse.de>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

    ---
    drivers/md/raid5.c | 42 +++++++++++++++++++++++++++++++++++++++---
    1 file changed, 39 insertions(+), 3 deletions(-)

    --- linux-2.6.20.1.orig/drivers/md/raid5.c
    +++ linux-2.6.20.1/drivers/md/raid5.c
    @@ -2620,7 +2620,7 @@ static struct bio *remove_bio_from_retry
    }
    bi = conf->retry_read_aligned_list;
    if(bi) {
    - conf->retry_read_aligned = bi->bi_next;
    + conf->retry_read_aligned_list = bi->bi_next;
    bi->bi_next = NULL;
    bi->bi_phys_segments = 1; /* biased count of active stripes */
    bi->bi_hw_segments = 0; /* count of processed stripes */
    @@ -2669,6 +2669,27 @@ static int raid5_align_endio(struct bio
    return 0;
    }

    +static int bio_fits_rdev(struct bio *bi)
    +{
    + request_queue_t *q = bdev_get_queue(bi->bi_bdev);
    +
    + if ((bi->bi_size>>9) > q->max_sectors)
    + return 0;
    + blk_recount_segments(q, bi);
    + if (bi->bi_phys_segments > q->max_phys_segments ||
    + bi->bi_hw_segments > q->max_hw_segments)
    + return 0;
    +
    + if (q->merge_bvec_fn)
    + /* it's too hard to apply the merge_bvec_fn at this stage,
    + * just just give up
    + */
    + return 0;
    +
    + return 1;
    +}
    +
    +
    static int chunk_aligned_read(request_queue_t *q, struct bio * raid_bio)
    {
    mddev_t *mddev = q->queuedata;
    @@ -2715,6 +2736,13 @@ static int chunk_aligned_read(request_qu
    align_bi->bi_flags &= ~(1 << BIO_SEG_VALID);
    align_bi->bi_sector += rdev->data_offset;

    + if (!bio_fits_rdev(align_bi)) {
    + /* too big in some way */
    + bio_put(align_bi);
    + rdev_dec_pending(rdev, mddev);
    + return 0;
    + }
    +
    spin_lock_irq(&conf->device_lock);
    wait_event_lock_irq(conf->wait_for_stripe,
    conf->quiesce == 0,
    @@ -3107,7 +3135,9 @@ static int retry_aligned_read(raid5_con
    last_sector = raid_bio->bi_sector + (raid_bio->bi_size>>9);

    for (; logical_sector < last_sector;
    - logical_sector += STRIPE_SECTORS, scnt++) {
    + logical_sector += STRIPE_SECTORS,
    + sector += STRIPE_SECTORS,
    + scnt++) {

    if (scnt < raid_bio->bi_hw_segments)
    /* already done this stripe */
    @@ -3123,7 +3153,13 @@ static int retry_aligned_read(raid5_con
    }

    set_bit(R5_ReadError, &sh->dev[dd_idx].flags);
    - add_stripe_bio(sh, raid_bio, dd_idx, 0);
    + if (!add_stripe_bio(sh, raid_bio, dd_idx, 0)) {
    + release_stripe(sh);
    + raid_bio->bi_hw_segments = scnt;
    + conf->retry_read_aligned = raid_bio;
    + return handled;
    + }
    +
    handle_stripe(sh, NULL);
    release_stripe(sh);
    handled++;
    --
    -
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