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") 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: Ming Lei ming.lei@redhat.com --- drivers/block/loop.c | 33 ++++++++++++++++++--------------- 1 file changed, 18 insertions(+), 15 deletions(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c index 2f137d6ce169..3d7a1901bf28 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -878,6 +878,7 @@ static void loop_config_discard(struct loop_device *lo) 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 @@ -890,11 +891,10 @@ static void loop_config_discard(struct loop_device *lo) 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 @@ -903,23 +903,26 @@ static void loop_config_discard(struct loop_device *lo) * 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)