From a84d5d429f9eb56f81b388609841ed993f0ddfca Mon Sep 17 00:00:00 2001 From: Boris Burkov Date: Tue, 18 Aug 2020 11:00:05 -0700 Subject: btrfs: detect nocow for swap after snapshot delete can_nocow_extent and btrfs_cross_ref_exist both rely on a heuristic for detecting a must cow condition which is not exactly accurate, but saves unnecessary tree traversal. The incorrect assumption is that if the extent was created in a generation smaller than the last snapshot generation, it must be referenced by that snapshot. That is true, except the snapshot could have since been deleted, without affecting the last snapshot generation. The original patch claimed a performance win from this check, but it also leads to a bug where you are unable to use a swapfile if you ever snapshotted the subvolume it's in. Make the check slower and more strict for the swapon case, without modifying the general cow checks as a compromise. Turning swap on does not seem to be a particularly performance sensitive operation, so incurring a possibly unnecessary btrfs_search_slot seems worthwhile for the added usability. Note: Until the snapshot is competely cleaned after deletion, check_committed_refs will still cause the logic to think that cow is necessary, so the user must until 'btrfs subvolu sync' finished before activating the swapfile swapon. CC: stable@vger.kernel.org # 5.4+ Suggested-by: Omar Sandoval Signed-off-by: Boris Burkov Signed-off-by: David Sterba --- fs/btrfs/extent-tree.c | 17 +++++++++++------ 1 file changed, 11 insertions(+), 6 deletions(-) (limited to 'fs/btrfs/extent-tree.c') diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c index de6fe176fdfb..5871ef78edba 100644 --- a/fs/btrfs/extent-tree.c +++ b/fs/btrfs/extent-tree.c @@ -2306,7 +2306,8 @@ static noinline int check_delayed_ref(struct btrfs_root *root, static noinline int check_committed_ref(struct btrfs_root *root, struct btrfs_path *path, - u64 objectid, u64 offset, u64 bytenr) + u64 objectid, u64 offset, u64 bytenr, + bool strict) { struct btrfs_fs_info *fs_info = root->fs_info; struct btrfs_root *extent_root = fs_info->extent_root; @@ -2348,9 +2349,13 @@ static noinline int check_committed_ref(struct btrfs_root *root, btrfs_extent_inline_ref_size(BTRFS_EXTENT_DATA_REF_KEY)) goto out; - /* If extent created before last snapshot => it's definitely shared */ - if (btrfs_extent_generation(leaf, ei) <= - btrfs_root_last_snapshot(&root->root_item)) + /* + * If extent created before last snapshot => it's shared unless the + * snapshot has been deleted. Use the heuristic if strict is false. + */ + if (!strict && + (btrfs_extent_generation(leaf, ei) <= + btrfs_root_last_snapshot(&root->root_item))) goto out; iref = (struct btrfs_extent_inline_ref *)(ei + 1); @@ -2375,7 +2380,7 @@ out: } int btrfs_cross_ref_exist(struct btrfs_root *root, u64 objectid, u64 offset, - u64 bytenr) + u64 bytenr, bool strict) { struct btrfs_path *path; int ret; @@ -2386,7 +2391,7 @@ int btrfs_cross_ref_exist(struct btrfs_root *root, u64 objectid, u64 offset, do { ret = check_committed_ref(root, path, objectid, - offset, bytenr); + offset, bytenr, strict); if (ret && ret != -ENOENT) goto out; -- cgit v1.2.3 From ad24466588ab7d7c879053c5afd919b0c555fec0 Mon Sep 17 00:00:00 2001 From: Josef Bacik Date: Mon, 10 Aug 2020 11:42:30 -0400 Subject: btrfs: set the correct lockdep class for new nodes When flipping over to the rw_semaphore I noticed I'd get a lockdep splat in replace_path(), which is weird because we're swapping the reloc root with the actual target root. Turns out this is because we're using the root->root_key.objectid as the root id for the newly allocated tree block when setting the lockdep class, however we need to be using the actual owner of this new block, which is saved in owner. The affected path is through btrfs_copy_root as all other callers of btrfs_alloc_tree_block (which calls init_new_buffer) have root_objectid == root->root_key.objectid . CC: stable@vger.kernel.org # 5.4+ Reviewed-by: Filipe Manana Reviewed-by: Nikolay Borisov Signed-off-by: Josef Bacik Reviewed-by: David Sterba Signed-off-by: David Sterba --- fs/btrfs/extent-tree.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'fs/btrfs/extent-tree.c') diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c index 5871ef78edba..e9eedc053fc5 100644 --- a/fs/btrfs/extent-tree.c +++ b/fs/btrfs/extent-tree.c @@ -4527,7 +4527,7 @@ btrfs_init_new_buffer(struct btrfs_trans_handle *trans, struct btrfs_root *root, return ERR_PTR(-EUCLEAN); } - btrfs_set_buffer_lockdep_class(root->root_key.objectid, buf, level); + btrfs_set_buffer_lockdep_class(owner, buf, level); btrfs_tree_lock(buf); btrfs_clean_tree_block(buf); clear_bit(EXTENT_BUFFER_STALE, &buf->bflags); -- cgit v1.2.3