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dm cache metadata: save in-core policy_hint_size to on-disk superblock 

policy_hint_size starts as 0 during __write_initial_superblock().  It
isn't until the policy is loaded that policy_hint_size is set in-core
(cmd->policy_hint_size).  But it never got recorded in the on-disk
superblock because __commit_transaction() didn't deal with transfering
the in-core cmd->policy_hint_size to the on-disk superblock.

The in-core cmd->policy_hint_size gets initialized by metadata_open()'s
__begin_transaction_flags() which re-reads all superblock fields.
Because the superblock's policy_hint_size was never properly stored, when
the cache was created, hints_array_available() would always return false
when re-activating a previously created cache.  This means
__load_mappings() always considered the hints invalid and never made use
of the hints (these hints served to optimize).

Another detremental side-effect of this oversight is the cache_check
utility would fail with: "invalid hint width: 0"

Cc: stable@vger.kernel.org
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
zero-colors
Mike Snitzer 2018-08-02 16:08:52 -04:00
parent 75294442d8
commit fd2fa95416
1 changed files with 2 additions and 1 deletions
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3
drivers/md/dm-cache-metadata.c
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@ -363,7 +363,7 @@ static int __write_initial_superblock(struct dm_cache_metadata *cmd)
disk_super->version = cpu_to_le32(cmd->version);
memset(disk_super->policy_name, 0, sizeof(disk_super->policy_name));
memset(disk_super->policy_version, 0, sizeof(disk_super->policy_version));
disk_super->policy_hint_size = 0;
disk_super->policy_hint_size = cpu_to_le32(0);
__copy_sm_root(cmd, disk_super);
@ -701,6 +701,7 @@ static int __commit_transaction(struct dm_cache_metadata *cmd,
disk_super->policy_version[0] = cpu_to_le32(cmd->policy_version[0]);
disk_super->policy_version[1] = cpu_to_le32(cmd->policy_version[1]);
disk_super->policy_version[2] = cpu_to_le32(cmd->policy_version[2]);
disk_super->policy_hint_size = cpu_to_le32(cmd->policy_hint_size);
disk_super->read_hits = cpu_to_le32(cmd->stats.read_hits);
disk_super->read_misses = cpu_to_le32(cmd->stats.read_misses);