5.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: Ming-Hung Tsai mtsai@redhat.com
[ Upstream commit 0bb1968da2737ba68fd63857d1af2b301a18d3bf ]
dm_array_cursor_skip() seeks to the target position by loading array blocks iteratively until the specified number of entries to skip is reached. When seeking across block boundaries, it uses dm_array_cursor_next() to step into the next block. dm_array_cursor_skip() must first move the cursor index to the end of the current block; otherwise, the cursor position could incorrectly remain in the same block, causing the actual number of skipped entries to be much smaller than expected.
This bug affects cache resizing in v2 metadata and could lead to data loss if the fast device is shrunk during the first-time resume. For example:
1. create a cache metadata consists of 32768 blocks, with a dirty block assigned to the second bitmap block. cache_restore v1.0 is required.
cat <<EOF >> cmeta.xml <superblock uuid="" block_size="64" nr_cache_blocks="32768" \ policy="smq" hint_width="4"> <mappings> <mapping cache_block="32767" origin_block="0" dirty="true"/> </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
2. bring up the cache while attempt to discard all the blocks belonging to the second bitmap block (block# 32576 to 32767). The last command is expected to fail, but it actually succeeds.
dmsetup create cdata --table "0 2084864 linear /dev/sdc 8192" dmsetup create corig --table "0 65536 linear /dev/sdc 2105344" dmsetup create cache --table "0 65536 cache /dev/mapper/cmeta \ /dev/mapper/cdata /dev/mapper/corig 64 2 metadata2 writeback smq \ 2 migration_threshold 0"
In addition to the reproducer described above, this fix can be verified using the "array_cursor/skip" tests in dm-unit: dm-unit run /pdata/array_cursor/skip/ --kernel-dir <KERNEL_DIR>
Signed-off-by: Ming-Hung Tsai mtsai@redhat.com Fixes: 9b696229aa7d ("dm persistent data: add cursor skip functions to the cursor APIs") Reviewed-by: Joe Thornber thornber@redhat.com Signed-off-by: Mike Snitzer snitzer@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/md/persistent-data/dm-array.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/drivers/md/persistent-data/dm-array.c b/drivers/md/persistent-data/dm-array.c index f97de343a398..4d434d89eadd 100644 --- a/drivers/md/persistent-data/dm-array.c +++ b/drivers/md/persistent-data/dm-array.c @@ -993,6 +993,7 @@ int dm_array_cursor_skip(struct dm_array_cursor *c, uint32_t count) }
count -= remaining; + c->index += (remaining - 1); r = dm_array_cursor_next(c);
} while (!r);