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    Subject[PATCH 4.14 31/89] dm cache metadata: save in-core policy_hint_size to on-disk superblock
    Date
    4.14-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Mike Snitzer <snitzer@redhat.com>

    commit fd2fa95416188a767a63979296fa3e169a9ef5ec upstream.

    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>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/md/dm-cache-metadata.c | 3 ++-
    1 file changed, 2 insertions(+), 1 deletion(-)

    --- a/drivers/md/dm-cache-metadata.c
    +++ b/drivers/md/dm-cache-metadata.c
    @@ -362,7 +362,7 @@ static int __write_initial_superblock(st
    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);

    @@ -700,6 +700,7 @@ static int __commit_transaction(struct d
    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);

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