From: Coly Li colyli@suse.de
[ Upstream commit 117f636ea695270fe492d0c0c9dfadc7a662af47 ]
In register_cache_set(), c is pointer to struct cache_set, and ca is pointer to struct cache, if ca->sb.seq > c->sb.seq, it means this registering cache has up to date version and other members, the in- memory version and other members should be updated to the newer value.
But current implementation makes a cache set only has a single cache device, so the above assumption works well except for a special case. The execption is when a cache device new created and both ca->sb.seq and c->sb.seq are 0, because the super block is never flushed out yet. In the location for the following if() check, 2156 if (ca->sb.seq > c->sb.seq) { 2157 c->sb.version = ca->sb.version; 2158 memcpy(c->sb.set_uuid, ca->sb.set_uuid, 16); 2159 c->sb.flags = ca->sb.flags; 2160 c->sb.seq = ca->sb.seq; 2161 pr_debug("set version = %llu\n", c->sb.version); 2162 } c->sb.version is not initialized yet and valued 0. When ca->sb.seq is 0, the if() check will fail (because both values are 0), and the cache set version, set_uuid, flags and seq won't be updated.
The above problem is hiden for current code, because the bucket size is compatible among different super block version. And the next time when running cache set again, ca->sb.seq will be larger than 0 and cache set super block version will be updated properly.
But if the large bucket feature is enabled, sb->bucket_size is the low 16bits of the bucket size. For a power of 2 value, when the actual bucket size exceeds 16bit width, sb->bucket_size will always be 0. Then read_super_common() will fail because the if() check to is_power_of_2(sb->bucket_size) is false. This is how the long time hidden bug is triggered.
This patch modifies the if() check to the following way, 2156 if (ca->sb.seq > c->sb.seq || c->sb.seq == 0) { Then cache set's version, set_uuid, flags and seq will always be updated corectly including for a new created cache device.
Signed-off-by: Coly Li colyli@suse.de Reviewed-by: Hannes Reinecke hare@suse.de Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/md/bcache/super.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c index 526e9d5a4fb16..2c976cf361984 100644 --- a/drivers/md/bcache/super.c +++ b/drivers/md/bcache/super.c @@ -1778,7 +1778,14 @@ static const char *register_cache_set(struct cache *ca) sysfs_create_link(&c->kobj, &ca->kobj, buf)) goto err;
- if (ca->sb.seq > c->sb.seq) { + /* + * A special case is both ca->sb.seq and c->sb.seq are 0, + * such condition happens on a new created cache device whose + * super block is never flushed yet. In this case c->sb.version + * and other members should be updated too, otherwise we will + * have a mistaken super block version in cache set. + */ + if (ca->sb.seq > c->sb.seq || c->sb.seq == 0) { c->sb.version = ca->sb.version; memcpy(c->sb.set_uuid, ca->sb.set_uuid, 16); c->sb.flags = ca->sb.flags;