A cache device failing to resume due to mapping errors should not be
retried, as the failure leaves a partially initialized policy object.
Repeating the resume operation risks triggering BUG_ON when reloading
cache mappings into the incomplete policy object.
Reproduce steps:
1. create a cache metadata consisting of 512 or more cache blocks,
with some mappings stored in the first array block of the mapping
array. Here we use cache_restore v1.0 to build the metadata.
cat <<EOF >> cmeta.xml
<superblock uuid="" block_size="128" nr_cache_blocks="512" \
policy="smq" hint_width="4">
<mappings>
<mapping cache_block="0" origin_block="0" dirty="false"/>
</mappings>
</superblock>
EOF
dmsetup create cmeta --table "0 8192 linear /dev/sdc 0"
cache_restore -i cmeta.xml -o /dev/mapper/cmeta --metadata-version=2
dmsetup remove cmeta
2. wipe the second array block of the mapping array to simulate
data degradations.
mapping_root=$(dd if=/dev/sdc bs=1c count=8 skip=192 \
2>/dev/null | hexdump -e '1/8 "%u\n"')
ablock=$(dd if=/dev/sdc bs=1c count=8 skip=$((4096*mapping_root+2056)) \
2>/dev/null | hexdump -e '1/8 "%u\n"')
dd if=/dev/zero of=/dev/sdc bs=4k count=1 seek=$ablock
3. try bringing up the cache device. The resume is expected to fail
due to the broken array block.
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"
dmsetup create cache --notable
dmsetup load cache --table "0 524288 cache /dev/mapper/cmeta \
/dev/mapper/cdata /dev/mapper/corig 128 2 metadata2 writethrough smq 0"
dmsetup resume cache
4. try resuming the cache again. An unexpected BUG_ON is triggered
while loading cache mappings.
dmsetup resume cache
Kernel logs:
(snip)
------------[ cut here ]------------
kernel BUG at drivers/md/dm-cache-policy-smq.c:752!
Oops: invalid opcode: 0000 [#1] PREEMPT SMP KASAN NOPTI
CPU: 0 UID: 0 PID: 332 Comm: dmsetup Not tainted 6.13.4 #3
RIP: 0010:smq_load_mapping+0x3e5/0x570
Fix by disallowing resume operations for devices that failed the
initial attempt.
Signed-off-by: Ming-Hung Tsai <mtsai@xxxxxxxxxx>
---
drivers/md/dm-cache-target.c | 24 ++++++++++++++++++++++++
1 file changed, 24 insertions(+)
diff --git a/drivers/md/dm-cache-target.c b/drivers/md/dm-cache-target.c
index 9cb797a561d6..6cee5eac8b9e 100644
--- a/drivers/md/dm-cache-target.c
+++ b/drivers/md/dm-cache-target.c
@@ -2899,6 +2899,27 @@ static dm_cblock_t get_cache_dev_size(struct cache *cache)
return to_cblock(size);
}
+static bool can_resume(struct cache *cache)
+{
+ /*
+ * Disallow retrying the resume operation for devices that failed the
+ * first resume attempt, as the failure leaves the policy object partially
+ * initialized. Retrying could trigger BUG_ON when loading cache mappings
+ * into the incomplete policy object.
+ */
+ if (cache->sized && !cache->loaded_mappings) {
+ if (get_cache_mode(cache) != CM_WRITE)
+ DMERR("%s: unable to resume a failed-loaded cache, please check metadata.",
+ cache_device_name(cache));
+ else
+ DMERR("%s: unable to resume cache due to missing proper cache table reload",
+ cache_device_name(cache));
+ return false;
+ }
+
+ return true;
+}
+
static bool can_resize(struct cache *cache, dm_cblock_t new_size)
{
if (from_cblock(new_size) > from_cblock(cache->cache_size)) {
@@ -2947,6 +2968,9 @@ static int cache_preresume(struct dm_target *ti)
struct cache *cache = ti->private;
dm_cblock_t csize = get_cache_dev_size(cache);
+ if (!can_resume(cache))
+ return -EINVAL;
+
/*
* Check to see if the cache has resized.
*/
--
2.47.0
