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    Subject[PATCH 5.8 169/255] block: loop: set discard granularity and alignment for block device backed loop
    Date
    From: Ming Lei <ming.lei@redhat.com>

    commit bcb21c8cc9947286211327d663ace69f07d37a76 upstream.

    In case of block device backend, if the backend supports write zeros, the
    loop device will set queue flag of QUEUE_FLAG_DISCARD. However,
    limits.discard_granularity isn't setup, and this way is wrong,
    see the following description in Documentation/ABI/testing/sysfs-block:

    A discard_granularity of 0 means that the device does not support
    discard functionality.

    Especially 9b15d109a6b2 ("block: improve discard bio alignment in
    __blkdev_issue_discard()") starts to take q->limits.discard_granularity
    for computing max discard sectors. And zero discard granularity may cause
    kernel oops, or fail discard request even though the loop queue claims
    discard support via QUEUE_FLAG_DISCARD.

    Fix the issue by setup discard granularity and alignment.

    Fixes: c52abf563049 ("loop: Better discard support for block devices")
    Signed-off-by: Ming Lei <ming.lei@redhat.com>
    Reviewed-by: Christoph Hellwig <hch@lst.de>
    Acked-by: Coly Li <colyli@suse.de>
    Cc: Hannes Reinecke <hare@suse.com>
    Cc: Xiao Ni <xni@redhat.com>
    Cc: Martin K. Petersen <martin.petersen@oracle.com>
    Cc: Evan Green <evgreen@chromium.org>
    Cc: Gwendal Grignou <gwendal@chromium.org>
    Cc: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
    Cc: Andrzej Pietrasiewicz <andrzej.p@collabora.com>
    Cc: Christoph Hellwig <hch@lst.de>
    Cc: <stable@vger.kernel.org>
    Signed-off-by: Jens Axboe <axboe@kernel.dk>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/block/loop.c | 33 ++++++++++++++++++---------------
    1 file changed, 18 insertions(+), 15 deletions(-)

    --- a/drivers/block/loop.c
    +++ b/drivers/block/loop.c
    @@ -877,6 +877,7 @@ static void loop_config_discard(struct l
    struct file *file = lo->lo_backing_file;
    struct inode *inode = file->f_mapping->host;
    struct request_queue *q = lo->lo_queue;
    + u32 granularity, max_discard_sectors;

    /*
    * If the backing device is a block device, mirror its zeroing
    @@ -889,11 +890,10 @@ static void loop_config_discard(struct l
    struct request_queue *backingq;

    backingq = bdev_get_queue(inode->i_bdev);
    - blk_queue_max_discard_sectors(q,
    - backingq->limits.max_write_zeroes_sectors);

    - blk_queue_max_write_zeroes_sectors(q,
    - backingq->limits.max_write_zeroes_sectors);
    + max_discard_sectors = backingq->limits.max_write_zeroes_sectors;
    + granularity = backingq->limits.discard_granularity ?:
    + queue_physical_block_size(backingq);

    /*
    * We use punch hole to reclaim the free space used by the
    @@ -902,23 +902,26 @@ static void loop_config_discard(struct l
    * useful information.
    */
    } else if (!file->f_op->fallocate || lo->lo_encrypt_key_size) {
    - q->limits.discard_granularity = 0;
    - q->limits.discard_alignment = 0;
    - blk_queue_max_discard_sectors(q, 0);
    - blk_queue_max_write_zeroes_sectors(q, 0);
    + max_discard_sectors = 0;
    + granularity = 0;

    } else {
    - q->limits.discard_granularity = inode->i_sb->s_blocksize;
    - q->limits.discard_alignment = 0;
    -
    - blk_queue_max_discard_sectors(q, UINT_MAX >> 9);
    - blk_queue_max_write_zeroes_sectors(q, UINT_MAX >> 9);
    + max_discard_sectors = UINT_MAX >> 9;
    + granularity = inode->i_sb->s_blocksize;
    }

    - if (q->limits.max_write_zeroes_sectors)
    + if (max_discard_sectors) {
    + q->limits.discard_granularity = granularity;
    + blk_queue_max_discard_sectors(q, max_discard_sectors);
    + blk_queue_max_write_zeroes_sectors(q, max_discard_sectors);
    blk_queue_flag_set(QUEUE_FLAG_DISCARD, q);
    - else
    + } else {
    + q->limits.discard_granularity = 0;
    + blk_queue_max_discard_sectors(q, 0);
    + blk_queue_max_write_zeroes_sectors(q, 0);
    blk_queue_flag_clear(QUEUE_FLAG_DISCARD, q);
    + }
    + q->limits.discard_alignment = 0;
    }

    static void loop_unprepare_queue(struct loop_device *lo)

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