From: Filipe Manana fdmanana@suse.com

commit d47704bd1c78c85831561bcf701b90dd66f811b2 upstream.

At find_delalloc_subrange(), when we need to get the next extent map, we do a full search on the extent map tree (a red black tree). This is fine but it's a lot more efficient to simply use rb_next(), which typically requires iterating over less nodes of the tree and never needs to compare the ranges of nodes with the one we are looking for.

So add a public helper to extent_map.{h,c} to get the extent map that immediately follows another extent map, using rb_next(), and use that helper at find_delalloc_subrange().

Signed-off-by: Filipe Manana fdmanana@suse.com Signed-off-by: David Sterba dsterba@suse.com ---

Please add this patch to the next 6.1 stable release. It happens to fix a bug recently reported at:

https://bugzilla.redhat.com/show_bug.cgi?id=2187312

Thanks.

fs/btrfs/extent_map.c | 31 +++++++++++++++++++++++++++++- fs/btrfs/extent_map.h | 2 ++ fs/btrfs/file.c | 44 ++++++++++++++++++++++++++----------------- 3 files changed, 59 insertions(+), 18 deletions(-)

diff --git a/fs/btrfs/extent_map.c b/fs/btrfs/extent_map.c index b8ae02aa632e..4abbe4b35253 100644 --- a/fs/btrfs/extent_map.c +++ b/fs/btrfs/extent_map.c @@ -523,7 +523,7 @@ void replace_extent_mapping(struct extent_map_tree *tree, setup_extent_mapping(tree, new, modified); }

-static struct extent_map *next_extent_map(struct extent_map *em) +static struct extent_map *next_extent_map(const struct extent_map *em) { struct rb_node *next;

@@ -533,6 +533,35 @@ static struct extent_map *next_extent_map(struct extent_map *em) return container_of(next, struct extent_map, rb_node); }

+/* + * Get the extent map that immediately follows another one. + * + * @tree: The extent map tree that the extent map belong to. + * Holding read or write access on the tree's lock is required. + * @em: An extent map from the given tree. The caller must ensure that + * between getting @em and between calling this function, the + * extent map @em is not removed from the tree - for example, by + * holding the tree's lock for the duration of those 2 operations. + * + * Returns the extent map that immediately follows @em, or NULL if @em is the + * last extent map in the tree. + */ +struct extent_map *btrfs_next_extent_map(const struct extent_map_tree *tree, + const struct extent_map *em) +{ + struct extent_map *next; + + /* The lock must be acquired either in read mode or write mode. */ + lockdep_assert_held(&tree->lock); + ASSERT(extent_map_in_tree(em)); + + next = next_extent_map(em); + if (next) + refcount_inc(&next->refs); + + return next; +} + static struct extent_map *prev_extent_map(struct extent_map *em) { struct rb_node *prev; diff --git a/fs/btrfs/extent_map.h b/fs/btrfs/extent_map.h index ad311864272a..68d3f2c9ea1d 100644 --- a/fs/btrfs/extent_map.h +++ b/fs/btrfs/extent_map.h @@ -87,6 +87,8 @@ static inline u64 extent_map_block_end(struct extent_map *em) void extent_map_tree_init(struct extent_map_tree *tree); struct extent_map *lookup_extent_mapping(struct extent_map_tree *tree, u64 start, u64 len); +struct extent_map *btrfs_next_extent_map(const struct extent_map_tree *tree, + const struct extent_map *em); int add_extent_mapping(struct extent_map_tree *tree, struct extent_map *em, int modified); void remove_extent_mapping(struct extent_map_tree *tree, struct extent_map *em); diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c index 1bda59c68360..77202addead8 100644 --- a/fs/btrfs/file.c +++ b/fs/btrfs/file.c @@ -3248,40 +3248,50 @@ static bool find_delalloc_subrange(struct btrfs_inode *inode, u64 start, u64 end */ read_lock(&em_tree->lock); em = lookup_extent_mapping(em_tree, start, len); - read_unlock(&em_tree->lock); + if (!em) { + read_unlock(&em_tree->lock); + return (delalloc_len > 0); + }

/* extent_map_end() returns a non-inclusive end offset. */ - em_end = em ? extent_map_end(em) : 0; + em_end = extent_map_end(em);

/* * If we have a hole/prealloc extent map, check the next one if this one * ends before our range's end. */ - if (em && (em->block_start == EXTENT_MAP_HOLE || - test_bit(EXTENT_FLAG_PREALLOC, &em->flags)) && em_end < end) { + if ((em->block_start == EXTENT_MAP_HOLE || + test_bit(EXTENT_FLAG_PREALLOC, &em->flags)) && em_end < end) { struct extent_map *next_em;

- read_lock(&em_tree->lock); - next_em = lookup_extent_mapping(em_tree, em_end, len - em_end); - read_unlock(&em_tree->lock); - + next_em = btrfs_next_extent_map(em_tree, em); free_extent_map(em); - em_end = next_em ? extent_map_end(next_em) : 0; + + /* + * There's no next extent map or the next one starts beyond our + * range, return the range found in the io tree (if any). + */ + if (!next_em || next_em->start > end) { + read_unlock(&em_tree->lock); + free_extent_map(next_em); + return (delalloc_len > 0); + } + + em_end = extent_map_end(next_em); em = next_em; }

- if (em && (em->block_start == EXTENT_MAP_HOLE || - test_bit(EXTENT_FLAG_PREALLOC, &em->flags))) { - free_extent_map(em); - em = NULL; - } + read_unlock(&em_tree->lock);

/* - * No extent map or one for a hole or prealloc extent. Use the delalloc - * range we found in the io tree if we have one. + * We have a hole or prealloc extent that ends at or beyond our range's + * end, return the range found in the io tree (if any). */ - if (!em) + if (em->block_start == EXTENT_MAP_HOLE || + test_bit(EXTENT_FLAG_PREALLOC, &em->flags)) { + free_extent_map(em); return (delalloc_len > 0); + }

/* * We don't have any range as EXTENT_DELALLOC in the io tree, so the