From 0d200aefd4ac51787b6b80de1bb7ce93bccd59f6 Mon Sep 17 00:00:00 2001 From: Joe Thornber Date: Tue, 3 Jul 2012 12:55:31 +0100 Subject: [PATCH] dm thin: commit metadata before creating metadata snapshot Userland sometimes sees a corrupt metadata block if metadata is changing rapidly when a metadata snapshot is reserved for userland, To make the problem go away, commit before we take the metadata snapshot (which is a sensible thing to do anyway). The checksums mean userland spots this corruption immediately so there's no risk of acting on incorrect data. No corruption exists from the kernel's point of view, and thin_check passes after pool shutdown. I believe this is to do with shared blocks at the first level of the {device, mapping} btree. Prior to the metadata-snap support no sharing at this level was possible, so this patch is only required after commit cc8394d86f045b86ff303d3c9e4ce47d97148951 ("dm thin: provide userspace access to pool metadata"). Signed-off-by: Joe Thornber Signed-off-by: Mike Snitzer Signed-off-by: Alasdair G Kergon --- drivers/md/dm-thin.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c index 37fdaf8..ce59824 100644 --- a/drivers/md/dm-thin.c +++ b/drivers/md/dm-thin.c @@ -2292,6 +2292,13 @@ static int process_reserve_metadata_snap_mesg(unsigned argc, char **argv, struct if (r) return r; + r = dm_pool_commit_metadata(pool->pmd); + if (r) { + DMERR("%s: dm_pool_commit_metadata() failed, error = %d", + __func__, r); + return r; + } + r = dm_pool_reserve_metadata_snap(pool->pmd); if (r) DMWARN("reserve_metadata_snap message failed."); -- 2.7.4