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    Subject[PATCH 5.4 030/177] dm snapshot: properly fix a crash when an origin has no snapshots
    Date
    From: Mikulas Patocka <mpatocka@redhat.com>

    commit 7e768532b2396bcb7fbf6f82384b85c0f1d2f197 upstream.

    If an origin target has no snapshots, o->split_boundary is set to 0.
    This causes BUG_ON(sectors <= 0) in block/bio.c:bio_split().

    Fix this by initializing chunk_size, and in turn split_boundary, to
    rounddown_pow_of_two(UINT_MAX) -- the largest power of two that fits
    into "unsigned" type.

    Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
    Cc: stable@vger.kernel.org
    Signed-off-by: Mike Snitzer <snitzer@redhat.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    drivers/md/dm-snap.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- a/drivers/md/dm-snap.c
    +++ b/drivers/md/dm-snap.c
    @@ -854,7 +854,7 @@ static int dm_add_exception(void *contex
    static uint32_t __minimum_chunk_size(struct origin *o)
    {
    struct dm_snapshot *snap;
    - unsigned chunk_size = 0;
    + unsigned chunk_size = rounddown_pow_of_two(UINT_MAX);

    if (o)
    list_for_each_entry(snap, &o->snapshots, list)

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