On 2020/8/5 11:50, Ming Lei wrote:
> 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")
> Cc: Coly Li <colyli@xxxxxxx>
> Cc: Hannes Reinecke <hare@xxxxxxxx>
> Cc: Xiao Ni <xni@xxxxxxxxxx>
> Cc: Martin K. Petersen <martin.petersen@xxxxxxxxxx>
> Cc: Evan Green <evgreen@xxxxxxxxxxxx>
> Cc: Gwendal Grignou <gwendal@xxxxxxxxxxxx>
> Cc: Chaitanya Kulkarni <chaitanya.kulkarni@xxxxxxx>
> Cc: Andrzej Pietrasiewicz <andrzej.p@xxxxxxxxxxxxx>
> Cc: Christoph Hellwig <hch@xxxxxx>
> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
> ---
> V2:
> - mirror backing queue's discard_granularity to loop queue
> - set discard limit parameters explicitly when QUEUE_FLAG_DISCARD is
> set
>
> 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 d18160146226..661c0814d63c 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);
I assume logical_block_size >= physical_block_size, maybe
queue_logical_block_size(backing) is better ?
I am not sure, just because I see nvme host driver and virtio block
driver use the logical block size, and scsi sd driver uses
max(physical_block_size, unmap_granularity * logical_block_size).
>
> /*
> * 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)
>
Overall the patch is good to me.
Acked-by: Coly Li <colyli@xxxxxxx>
Thanks.
Coly Li
