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    Subject[PATCH] dm.c - device-mapper I/O path fixes
    Date
    Joe, Linus,

    This patch fixes problems with the device-mapper I/O path in 2.5.51. The
    existing code does not properly split requests when necessary, and can
    cause segfaults and/or data corruption. This can easily manifest itself
    when running XFS on striped LVM volumes.

    Notes:
    - New bio's must be alloc'd instead of clone'd, since the bio vector may need
    to be adjusted if the end of the split request does not fill a page.
    - Fix reference counting of md->pending. This should only be incremented once
    for each incoming bio, not for each split bio that is resubmitted.
    - Copy the correct bvec when splitting the tail-end of a page.


    --
    Kevin Corry
    corryk@us.ibm.com
    http://evms.sourceforge.net/


    --- linux-2.5.51a/drivers/md/dm.c Tue Dec 10 11:01:13 2002
    +++ linux-2.5.51b/drivers/md/dm.c Tue Dec 10 11:03:55 2002
    @@ -242,17 +242,18 @@
    static spinlock_t _uptodate_lock = SPIN_LOCK_UNLOCKED;
    unsigned long flags;

    - spin_lock_irqsave(&_uptodate_lock, flags);
    - if (error)
    + if (error) {
    + spin_lock_irqsave(&_uptodate_lock, flags);
    io->error = error;
    - spin_unlock_irqrestore(&_uptodate_lock, flags);
    + spin_unlock_irqrestore(&_uptodate_lock, flags);
    + }

    if (atomic_dec_and_test(&io->io_count)) {
    if (atomic_dec_and_test(&io->md->pending))
    /* nudge anyone waiting on suspend queue */
    wake_up(&io->md->wait);

    - bio_endio(io->bio, io->error ? 0 : io->bio->bi_size, io->error);
    + bio_endio(io->bio, io->bio->bi_size, io->error);
    free_io(io);
    }
    }
    @@ -261,15 +262,15 @@
    {
    struct dm_io *io = bio->bi_private;

    - /*
    - * Only call dec_pending if the clone has completely
    - * finished. If a partial io errors I'm assuming it won't
    - * be requeued. FIXME: check this.
    - */
    - if (error || !bio->bi_size) {
    - dec_pending(io, error);
    - bio_put(bio);
    + if (bio->bi_size)
    + return 1;
    +
    + if (error) {
    + struct gendisk *disk = dm_disk(io->md);
    + DMWARN("I/O error (%d) on device %s\n", error, disk->disk_name);
    }
    + dec_pending(io, error);
    + bio_put(bio);

    return 0;
    }
    @@ -313,7 +314,6 @@
    * anything, the target has assumed ownership of
    * this io.
    */
    - atomic_inc(&io->md->pending);
    atomic_inc(&io->io_count);
    r = ti->type->map(ti, clone);
    if (r > 0)
    @@ -341,9 +341,7 @@
    {
    struct dm_target *ti = dm_table_find_target(ci->md->map, ci->sector);
    struct bio *clone, *bio = ci->bio;
    - struct bio_vec *bv = bio->bi_io_vec + (bio->bi_vcnt - 1);
    -
    - DMWARN("splitting page");
    + struct bio_vec *bv = bio->bi_io_vec + ci->idx;

    if (len > ci->sector_count)
    len = ci->sector_count;
    @@ -353,11 +351,13 @@

    clone->bi_sector = ci->sector;
    clone->bi_bdev = bio->bi_bdev;
    - clone->bi_flags = bio->bi_flags | (1 << BIO_SEG_VALID);
    clone->bi_rw = bio->bi_rw;
    + clone->bi_vcnt = 1;
    clone->bi_size = len << SECTOR_SHIFT;
    clone->bi_end_io = clone_endio;
    clone->bi_private = ci->io;
    + clone->bi_io_vec->bv_offset = clone->bi_io_vec->bv_len - clone->bi_size;
    + clone->bi_io_vec->bv_len = clone->bi_size;

    ci->sector += len;
    ci->sector_count -= len;
    @@ -369,24 +369,48 @@
    {
    struct bio *clone, *bio = ci->bio;
    struct dm_target *ti = dm_table_find_target(ci->md->map, ci->sector);
    - sector_t len = max_io_len(ci->md, bio->bi_sector, ti);
    + sector_t bv_len, len = max_io_len(ci->md, ci->sector, ti);
    + struct bio_vec *bv;
    + int i, vcnt = bio->bi_vcnt - ci->idx;

    /* shorter than current target ? */
    if (ci->sector_count < len)
    len = ci->sector_count;

    /* create the clone */
    - clone = bio_clone(ci->bio, GFP_NOIO);
    + clone = bio_alloc(GFP_NOIO, vcnt);
    + if (!clone) {
    + dec_pending(ci->io, -ENOMEM);
    + return;
    + }
    clone->bi_sector = ci->sector;
    - clone->bi_idx = ci->idx;
    + clone->bi_bdev = bio->bi_bdev;
    + clone->bi_rw = bio->bi_rw;
    + clone->bi_vcnt = vcnt;
    clone->bi_size = len << SECTOR_SHIFT;
    clone->bi_end_io = clone_endio;
    clone->bi_private = ci->io;

    + /* copy the original vector and adjust if necessary. */
    + memcpy(clone->bi_io_vec, bio->bi_io_vec + ci->idx,
    + vcnt * sizeof(*clone->bi_io_vec));
    + bv_len = len << SECTOR_SHIFT;
    + bio_for_each_segment(bv, clone, i) {
    + if (bv_len >= bv->bv_len) {
    + bv_len -= bv->bv_len;
    + } else {
    + bv->bv_len = bv_len;
    + clone->bi_vcnt = i + 1;
    + break;
    + }
    + }
    +
    + /* submit this io */
    + __map_bio(ti, clone);
    +
    /* adjust the remaining io */
    ci->sector += len;
    ci->sector_count -= len;
    - __map_bio(ti, clone);

    /*
    * If we are not performing all remaining io in this
    @@ -395,8 +419,8 @@
    */
    if (ci->sector_count) {
    while (len) {
    - struct bio_vec *bv = clone->bi_io_vec + ci->idx;
    - sector_t bv_len = bv->bv_len >> SECTOR_SHIFT;
    + bv = bio->bi_io_vec + ci->idx;
    + bv_len = bv->bv_len >> SECTOR_SHIFT;
    if (bv_len <= len)
    len -= bv_len;

    @@ -427,6 +451,8 @@
    ci.sector_count = bio_sectors(bio);
    ci.idx = 0;

    + atomic_inc(&ci.io->md->pending);
    +
    while (ci.sector_count)
    __clone_and_map(&ci);

    @@ -457,13 +483,13 @@
    up_read(&md->lock);

    if (bio_rw(bio) == READA) {
    - bio_io_error(bio, 0);
    + bio_io_error(bio, bio->bi_size);
    return 0;
    }

    r = queue_io(md, bio);
    if (r < 0) {
    - bio_io_error(bio, 0);
    + bio_io_error(bio, bio->bi_size);
    return 0;

    } else if (r == 0)
    -
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