• Dave Chinner's avatar
    block: fix 32 bit overflow in __blkdev_issue_discard() · 4800bf7b
    Dave Chinner authored
    A discard cleanup merged into 4.20-rc2 causes fstests xfs/259 to
    fall into an endless loop in the discard code. The test is creating
    a device that is exactly 2^32 sectors in size to test mkfs boundary
    conditions around the 32 bit sector overflow region.
    
    mkfs issues a discard for the entire device size by default, and
    hence this throws a sector count of 2^32 into
    blkdev_issue_discard(). It takes the number of sectors to discard as
    a sector_t - a 64 bit value.
    
    The commit ba5d7385 ("block: cleanup __blkdev_issue_discard")
    takes this sector count and casts it to a 32 bit value before
    comapring it against the maximum allowed discard size the device
    has. This truncates away the upper 32 bits, and so if the lower 32
    bits of the sector count is zero, it starts issuing discards of
    length 0. This causes the code to fall into an endless loop, issuing
    a zero length discards over and over again on the same sector.
    
    Fixes: ba5d7385 ("block: cleanup __blkdev_issue_discard")
    Tested-by: 's avatarDarrick J. Wong <darrick.wong@oracle.com>
    Reviewed-by: 's avatarDarrick J. Wong <darrick.wong@oracle.com>
    Signed-off-by: 's avatarDave Chinner <dchinner@redhat.com>
    
    Killed pointless WARN_ON().
    Signed-off-by: 's avatarJens Axboe <axboe@kernel.dk>
    4800bf7b