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    Subject[PATCH 3.19.y-ckt 041/102] dm: fix dm_merge_bvec regression on 32 bit systems
    Date
    3.19.8-ckt7 -stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Mike Snitzer <snitzer@redhat.com>

    commit bd4aaf8f9b85d6b2df3231fd62b219ebb75d3568 upstream.

    A DM regression on 32 bit systems was reported against v4.2-rc3 here:
    https://lkml.org/lkml/2015/7/29/401

    Fix this by reverting both commit 1c220c69 ("dm: fix casting bug in
    dm_merge_bvec()") and 148e51ba ("dm: improve documentation and code
    clarity in dm_merge_bvec"). This combined revert is done to eliminate
    the possibility of a partial revert in stable@ kernels.

    In hindsight the correct fix, at the time 1c220c69 was applied to fix
    the regression that 148e51ba introduced, should've been to simply revert
    148e51ba.

    Reported-by: Josh Boyer <jwboyer@fedoraproject.org>
    Tested-by: Adam Williamson <awilliam@redhat.com>
    Acked-by: Joe Thornber <ejt@redhat.com>
    Signed-off-by: Mike Snitzer <snitzer@redhat.com>
    Signed-off-by: Kamal Mostafa <kamal@canonical.com>
    ---
    drivers/md/dm.c | 27 ++++++++++-----------------
    1 file changed, 10 insertions(+), 17 deletions(-)

    diff --git a/drivers/md/dm.c b/drivers/md/dm.c
    index a367a17..82fe47d 100644
    --- a/drivers/md/dm.c
    +++ b/drivers/md/dm.c
    @@ -1596,7 +1596,8 @@ static int dm_merge_bvec(struct request_queue *q,
    struct mapped_device *md = q->queuedata;
    struct dm_table *map = dm_get_live_table_fast(md);
    struct dm_target *ti;
    - sector_t max_sectors, max_size = 0;
    + sector_t max_sectors;
    + int max_size = 0;

    if (unlikely(!map))
    goto out;
    @@ -1609,18 +1610,10 @@ static int dm_merge_bvec(struct request_queue *q,
    * Find maximum amount of I/O that won't need splitting
    */
    max_sectors = min(max_io_len(bvm->bi_sector, ti),
    - (sector_t) queue_max_sectors(q));
    + (sector_t) BIO_MAX_SECTORS);
    max_size = (max_sectors << SECTOR_SHIFT) - bvm->bi_size;
    -
    - /*
    - * FIXME: this stop-gap fix _must_ be cleaned up (by passing a sector_t
    - * to the targets' merge function since it holds sectors not bytes).
    - * Just doing this as an interim fix for stable@ because the more
    - * comprehensive cleanup of switching to sector_t will impact every
    - * DM target that implements a ->merge hook.
    - */
    - if (max_size > INT_MAX)
    - max_size = INT_MAX;
    + if (max_size < 0)
    + max_size = 0;

    /*
    * merge_bvec_fn() returns number of bytes
    @@ -1628,13 +1621,13 @@ static int dm_merge_bvec(struct request_queue *q,
    * max is precomputed maximal io size
    */
    if (max_size && ti->type->merge)
    - max_size = ti->type->merge(ti, bvm, biovec, (int) max_size);
    + max_size = ti->type->merge(ti, bvm, biovec, max_size);
    /*
    * If the target doesn't support merge method and some of the devices
    - * provided their merge_bvec method (we know this by looking for the
    - * max_hw_sectors that dm_set_device_limits may set), then we can't
    - * allow bios with multiple vector entries. So always set max_size
    - * to 0, and the code below allows just one page.
    + * provided their merge_bvec method (we know this by looking at
    + * queue_max_hw_sectors), then we can't allow bios with multiple vector
    + * entries. So always set max_size to 0, and the code below allows
    + * just one page.
    */
    else if (queue_max_hw_sectors(q) <= PAGE_SIZE >> 9)
    max_size = 0;
    --
    1.9.1


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