4.18-stable review patch. If anyone has any objections, please let me know.
------------------
From: Ilya Dryomov idryomov@gmail.com
commit 5b1fe7bec8a8d0cc547a22e7ddc2bd59acd67de4 upstream.
Quoting Documentation/device-mapper/cache.txt:
The 'dirty' state for a cache block changes far too frequently for us to keep updating it on the fly. So we treat it as a hint. In normal operation it will be written when the dm device is suspended. If the system crashes all cache blocks will be assumed dirty when restarted.
This got broken in commit f177940a8091 ("dm cache metadata: switch to using the new cursor api for loading metadata") in 4.9, which removed the code that consulted cmd->clean_when_opened (CLEAN_SHUTDOWN on-disk flag) when loading cache blocks. This results in data corruption on an unclean shutdown with dirty cache blocks on the fast device. After the crash those blocks are considered clean and may get evicted from the cache at any time. This can be demonstrated by doing a lot of reads to trigger individual evictions, but uncache is more predictable:
### Disable auto-activation in lvm.conf to be able to do uncache in ### time (i.e. see uncache doing flushing) when the fix is applied.
# xfs_io -d -c 'pwrite -b 4M -S 0xaa 0 1G' /dev/vdb # vgcreate vg_cache /dev/vdb /dev/vdc # lvcreate -L 1G -n lv_slowdev vg_cache /dev/vdb # lvcreate -L 512M -n lv_cachedev vg_cache /dev/vdc # lvcreate -L 256M -n lv_metadev vg_cache /dev/vdc # lvconvert --type cache-pool --cachemode writeback vg_cache/lv_cachedev --poolmetadata vg_cache/lv_metadev # lvconvert --type cache vg_cache/lv_slowdev --cachepool vg_cache/lv_cachedev # xfs_io -d -c 'pwrite -b 4M -S 0xbb 0 512M' /dev/mapper/vg_cache-lv_slowdev # xfs_io -d -c 'pread -v 254M 512' /dev/mapper/vg_cache-lv_slowdev | head -n 2 0fe00000: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb ................ 0fe00010: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb ................ # dmsetup status vg_cache-lv_slowdev 0 2097152 cache 8 27/65536 128 8192/8192 1 100 0 0 0 8192 7065 2 metadata2 writeback 2 migration_threshold 2048 smq 0 rw - ^^^^ 7065 * 64k = 441M yet to be written to the slow device # echo b >/proc/sysrq-trigger
# vgchange -ay vg_cache # xfs_io -d -c 'pread -v 254M 512' /dev/mapper/vg_cache-lv_slowdev | head -n 2 0fe00000: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb ................ 0fe00010: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb ................ # lvconvert --uncache vg_cache/lv_slowdev Flushing 0 blocks for cache vg_cache/lv_slowdev. Logical volume "lv_cachedev" successfully removed Logical volume vg_cache/lv_slowdev is not cached. # xfs_io -d -c 'pread -v 254M 512' /dev/mapper/vg_cache-lv_slowdev | head -n 2 0fe00000: aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa ................ 0fe00010: aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa ................
This is the case with both v1 and v2 cache pool metatata formats.
After applying this patch:
# vgchange -ay vg_cache # xfs_io -d -c 'pread -v 254M 512' /dev/mapper/vg_cache-lv_slowdev | head -n 2 0fe00000: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb ................ 0fe00010: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb ................ # lvconvert --uncache vg_cache/lv_slowdev Flushing 3724 blocks for cache vg_cache/lv_slowdev. ... Flushing 71 blocks for cache vg_cache/lv_slowdev. Logical volume "lv_cachedev" successfully removed Logical volume vg_cache/lv_slowdev is not cached. # xfs_io -d -c 'pread -v 254M 512' /dev/mapper/vg_cache-lv_slowdev | head -n 2 0fe00000: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb ................ 0fe00010: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb ................
Cc: stable@vger.kernel.org Fixes: f177940a8091 ("dm cache metadata: switch to using the new cursor api for loading metadata") Signed-off-by: Ilya Dryomov idryomov@gmail.com Signed-off-by: Mike Snitzer snitzer@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/md/dm-cache-metadata.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-)
--- a/drivers/md/dm-cache-metadata.c +++ b/drivers/md/dm-cache-metadata.c @@ -1323,6 +1323,7 @@ static int __load_mapping_v1(struct dm_c
dm_oblock_t oblock; unsigned flags; + bool dirty = true;
dm_array_cursor_get_value(mapping_cursor, (void **) &mapping_value_le); memcpy(&mapping, mapping_value_le, sizeof(mapping)); @@ -1333,8 +1334,10 @@ static int __load_mapping_v1(struct dm_c dm_array_cursor_get_value(hint_cursor, (void **) &hint_value_le); memcpy(&hint, hint_value_le, sizeof(hint)); } + if (cmd->clean_when_opened) + dirty = flags & M_DIRTY;
- r = fn(context, oblock, to_cblock(cb), flags & M_DIRTY, + r = fn(context, oblock, to_cblock(cb), dirty, le32_to_cpu(hint), hints_valid); if (r) { DMERR("policy couldn't load cache block %llu", @@ -1362,7 +1365,7 @@ static int __load_mapping_v2(struct dm_c
dm_oblock_t oblock; unsigned flags; - bool dirty; + bool dirty = true;
dm_array_cursor_get_value(mapping_cursor, (void **) &mapping_value_le); memcpy(&mapping, mapping_value_le, sizeof(mapping)); @@ -1373,8 +1376,9 @@ static int __load_mapping_v2(struct dm_c dm_array_cursor_get_value(hint_cursor, (void **) &hint_value_le); memcpy(&hint, hint_value_le, sizeof(hint)); } + if (cmd->clean_when_opened) + dirty = dm_bitset_cursor_get_value(dirty_cursor);
- dirty = dm_bitset_cursor_get_value(dirty_cursor); r = fn(context, oblock, to_cblock(cb), dirty, le32_to_cpu(hint), hints_valid); if (r) {