From: Nikos Tsironis ntsironis@arrikto.com
commit 2524933307fd0036d5c32357c693c021ab09a0b0 upstream.
In case of devices with at most 64 blocks, the digestion of consecutive eras uses the writeset of the first era as the writeset of all eras to digest, leading to lost writes. That is, we lose the information about what blocks were written during the affected eras.
The digestion code uses a dm_disk_bitset object to access the archived writesets. This structure includes a one word (64-bit) cache to reduce the number of array lookups.
This structure is initialized only once, in metadata_digest_start(), when we kick off digestion.
But, when we insert a new writeset into the writeset tree, before the digestion of the previous writeset is done, or equivalently when there are multiple writesets in the writeset tree to digest, then all these writesets are digested using the same cache and the cache is not re-initialized when moving from one writeset to the next.
For devices with more than 64 blocks, i.e., the size of the cache, the cache is indirectly invalidated when we move to a next set of blocks, so we avoid the bug.
But for devices with at most 64 blocks we end up using the same cached data for digesting all archived writesets, i.e., the cache is loaded when digesting the first writeset and it never gets reloaded, until the digestion is done.
As a result, the writeset of the first era to digest is used as the writeset of all the following archived eras, leading to lost writes.
Fix this by reinitializing the dm_disk_bitset structure, and thus invalidating the cache, every time the digestion code starts digesting a new writeset.
Fixes: eec40579d84873 ("dm: add era target") Cc: stable@vger.kernel.org # v3.15+ Signed-off-by: Nikos Tsironis ntsironis@arrikto.com Signed-off-by: Mike Snitzer snitzer@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/md/dm-era-target.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-)
--- a/drivers/md/dm-era-target.c +++ b/drivers/md/dm-era-target.c @@ -756,6 +756,12 @@ static int metadata_digest_lookup_writes ws_unpack(&disk, &d->writeset); d->value = cpu_to_le32(key);
+ /* + * We initialise another bitset info to avoid any caching side effects + * with the previous one. + */ + dm_disk_bitset_init(md->tm, &d->info); + d->nr_bits = min(d->writeset.nr_bits, md->nr_blocks); d->current_bit = 0; d->step = metadata_digest_transcribe_writeset; @@ -769,12 +775,6 @@ static int metadata_digest_start(struct return 0;
memset(d, 0, sizeof(*d)); - - /* - * We initialise another bitset info to avoid any caching side - * effects with the previous one. - */ - dm_disk_bitset_init(md->tm, &d->info); d->step = metadata_digest_lookup_writeset;
return 0;