ack
On Tue, Oct 22, 2024 at 8:12 AM Ming-Hung Tsai <mtsai@xxxxxxxxxx> wrote:
>
> When creating a cache device, the actual size of the cache origin might
> be greater than the specified cache target length. In such case, the
> number of origin blocks should match the cache target length, not the
> full size of the origin device, since access beyond the cache target is
> not possible. This issue occurs when reducing the origin device size
> using lvm, as lvreduce preloads the new cache table before resuming the
> cache origin, which can result in incorrect sizes for the discard bitset
> and smq hotspot blocks.
>
> Reproduce steps:
>
> 1. create a cache device consists of 4096 origin blocks
>
> dmsetup create cmeta --table "0 8192 linear /dev/sdc 0"
> dmsetup create cdata --table "0 65536 linear /dev/sdc 8192"
> dmsetup create corig --table "0 524288 linear /dev/sdc 262144"
> dd if=/dev/zero of=/dev/mapper/cmeta bs=4k count=1 oflag=direct
> dmsetup create cache --table "0 524288 cache /dev/mapper/cmeta \
> /dev/mapper/cdata /dev/mapper/corig 128 2 metadata2 writethrough smq 0"
>
> 2. reduce the cache origin to 2048 oblocks, in lvreduce's approach
>
> dmsetup reload corig --table "0 262144 linear /dev/sdc 262144"
> dmsetup reload cache --table "0 262144 cache /dev/mapper/cmeta \
> /dev/mapper/cdata /dev/mapper/corig 128 2 metadata2 writethrough smq 0"
> dmsetup suspend cache
> dmsetup suspend corig
> dmsetup suspend cdata
> dmsetup suspend cmeta
> dmsetup resume corig
> dmsetup resume cdata
> dmsetup resume cmeta
> dmsetup resume cache
>
> 3. shutdown the cache, and check the number of discard blocks in
> superblock. The value is expected to be 2048, but actually is 4096.
>
> dmsetup remove cache corig cdata cmeta
> dd if=/dev/sdc bs=1c count=8 skip=224 2>/dev/null | hexdump -e '1/8 "%u\n"'
>
> Fix by correcting the origin_blocks initialization in cache_create and
> removing the unused origin_sectors from struct cache_args accordingly.
>
> Signed-off-by: Ming-Hung Tsai <mtsai@xxxxxxxxxx>
> Fixes: c6b4fcbad044 ("dm: add cache target")
> ---
> drivers/md/dm-cache-target.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/md/dm-cache-target.c b/drivers/md/dm-cache-target.c
> index aaeeabfab09b..90772b42c234 100644
> --- a/drivers/md/dm-cache-target.c
> +++ b/drivers/md/dm-cache-target.c
> @@ -2003,7 +2003,6 @@ struct cache_args {
> sector_t cache_sectors;
>
> struct dm_dev *origin_dev;
> - sector_t origin_sectors;
>
> uint32_t block_size;
>
> @@ -2084,6 +2083,7 @@ static int parse_cache_dev(struct cache_args *ca, struct dm_arg_set *as,
> static int parse_origin_dev(struct cache_args *ca, struct dm_arg_set *as,
> char **error)
> {
> + sector_t origin_sectors;
> int r;
>
> if (!at_least_one_arg(as, error))
> @@ -2096,8 +2096,8 @@ static int parse_origin_dev(struct cache_args *ca, struct dm_arg_set *as,
> return r;
> }
>
> - ca->origin_sectors = get_dev_size(ca->origin_dev);
> - if (ca->ti->len > ca->origin_sectors) {
> + origin_sectors = get_dev_size(ca->origin_dev);
> + if (ca->ti->len > origin_sectors) {
> *error = "Device size larger than cached device";
> return -EINVAL;
> }
> @@ -2407,7 +2407,7 @@ static int cache_create(struct cache_args *ca, struct cache **result)
>
> ca->metadata_dev = ca->origin_dev = ca->cache_dev = NULL;
>
> - origin_blocks = cache->origin_sectors = ca->origin_sectors;
> + origin_blocks = cache->origin_sectors = ti->len;
> origin_blocks = block_div(origin_blocks, ca->block_size);
> cache->origin_blocks = to_oblock(origin_blocks);
>
> --
> 2.47.0
>
