From 683852c031c9dad34d4a2527de8c4b1ee4c8c2b5 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 9ac57871e4052b466de212631ebf12d1a1b31cab ("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 37fdaf81bd1f8..ce59824fb4140 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."); -- 2.39.5