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[76.182.20.124]) by smtp.gmail.com with ESMTPSA id m73-20020a0dca4c000000b005a7db2a0dddsm101985ywd.3.2023.10.10.13.41.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 10 Oct 2023 13:41:13 -0700 (PDT) From: Josef Bacik To: linux-fscrypt@vger.kernel.org, ebiggers@kernel.org, linux-btrfs@vger.kernel.org Subject: [PATCH v2 08/36] btrfs: add infrastructure for safe em freeing Date: Tue, 10 Oct 2023 16:40:23 -0400 Message-ID: X-Mailer: git-send-email 2.41.0 In-Reply-To: References: MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org When we add fscrypt support we're going to have fscrypt objects hanging off of extent_maps. This includes a block key, which if we're the last one freeing the key we may have to unregister it from the block layer. This requires taking a semaphore in the block layer, which means we can't free em's under the extent map tree lock. Thankfully we only do this in two places, one where we're dropping a range of extent maps, and when we're freeing logged extents. Add a free_extent_map_safe() which will add the em to a list in the em_tree if we free'd the object. Currently this is unconditional but will be changed to conditional on the fscrypt object we will add in a later patch. To process these delayed objects add a free_pending_extent_maps() that is called after the lock has been dropped on the em_tree. This will process the extent maps on the freed list and do the appropriate freeing work in a safe manner. Signed-off-by: Josef Bacik --- fs/btrfs/extent_map.c | 80 ++++++++++++++++++++++++++++++++++++++++--- fs/btrfs/extent_map.h | 10 ++++++ fs/btrfs/tree-log.c | 6 ++-- 3 files changed, 89 insertions(+), 7 deletions(-) diff --git a/fs/btrfs/extent_map.c b/fs/btrfs/extent_map.c index a6d8368ed0ed..af5ff6b10865 100644 --- a/fs/btrfs/extent_map.c +++ b/fs/btrfs/extent_map.c @@ -35,7 +35,9 @@ void __cold extent_map_exit(void) void extent_map_tree_init(struct extent_map_tree *tree) { tree->map = RB_ROOT_CACHED; + tree->flags = 0; INIT_LIST_HEAD(&tree->modified_extents); + INIT_LIST_HEAD(&tree->freed_extents); rwlock_init(&tree->lock); } @@ -53,9 +55,17 @@ struct extent_map *alloc_extent_map(void) em->compress_type = BTRFS_COMPRESS_NONE; refcount_set(&em->refs, 1); INIT_LIST_HEAD(&em->list); + INIT_LIST_HEAD(&em->free_list); return em; } +static void __free_extent_map(struct extent_map *em) +{ + if (test_bit(EXTENT_FLAG_FS_MAPPING, &em->flags)) + kfree(em->map_lookup); + kmem_cache_free(extent_map_cache, em); +} + /* * Drop the reference out on @em by one and free the structure if the reference * count hits zero. @@ -67,12 +77,69 @@ void free_extent_map(struct extent_map *em) if (refcount_dec_and_test(&em->refs)) { WARN_ON(extent_map_in_tree(em)); WARN_ON(!list_empty(&em->list)); - if (test_bit(EXTENT_FLAG_FS_MAPPING, &em->flags)) - kfree(em->map_lookup); - kmem_cache_free(extent_map_cache, em); + __free_extent_map(em); } } +/* + * Drop a ref for the extent map in the given tree. + * + * @tree: tree that the em is a part of. + * @em: the em to drop the reference to. + * + * Drop the reference count on @em by one, if the reference count hits 0 and + * there is an object on the em that can't be safely freed in the current + * context (if we are holding the extent_map_tree->lock for example), then add + * it to the freed_extents list on the extent_map_tree for later processing. + * + * This must be followed by a free_pending_extent_maps() to clear the pending + * frees. + */ +void free_extent_map_safe(struct extent_map_tree *tree, + struct extent_map *em) +{ + lockdep_assert_held_write(&tree->lock); + + if (!em) + return; + + if (refcount_dec_and_test(&em->refs)) { + WARN_ON(extent_map_in_tree(em)); + WARN_ON(!list_empty(&em->list)); + list_add_tail(&em->free_list, &tree->freed_extents); + set_bit(EXTENT_MAP_TREE_PENDING_FREES, &tree->flags); + } +} + +/* + * Free the em objects that exist on the em tree + * + * @tree: the tree to free the objects from. + * + * If there are any objects on the em->freed_extents list go ahead and free them + * here in a safe way. This is to be coupled with any uses of + * free_extent_map_safe(). + */ +void free_pending_extent_maps(struct extent_map_tree *tree) +{ + struct extent_map *em; + + /* Avoid taking the write lock if we don't have any pending frees. */ + if (!test_and_clear_bit(EXTENT_MAP_TREE_PENDING_FREES, &tree->flags)) + return; + + write_lock(&tree->lock); + while ((em = list_first_entry_or_null(&tree->freed_extents, + struct extent_map, free_list))) { + list_del_init(&em->free_list); + write_unlock(&tree->lock); + __free_extent_map(em); + cond_resched(); + write_lock(&tree->lock); + } + write_unlock(&tree->lock); +} + /* Do the math around the end of an extent, handling wrapping. */ static u64 range_end(u64 start, u64 len) { @@ -684,10 +751,12 @@ static void drop_all_extent_maps_fast(struct extent_map_tree *tree) clear_bit(EXTENT_FLAG_PINNED, &em->flags); clear_bit(EXTENT_FLAG_LOGGING, &em->flags); remove_extent_mapping(tree, em); - free_extent_map(em); + free_extent_map_safe(tree, em); cond_resched_rwlock_write(&tree->lock); } write_unlock(&tree->lock); + + free_pending_extent_maps(tree); } /* @@ -908,13 +977,14 @@ void btrfs_drop_extent_map_range(struct btrfs_inode *inode, u64 start, u64 end, free_extent_map(em); next: /* Once for us (for our lookup reference). */ - free_extent_map(em); + free_extent_map_safe(em_tree, em); em = next_em; } write_unlock(&em_tree->lock); + free_pending_extent_maps(em_tree); free_extent_map(split); free_extent_map(split2); } diff --git a/fs/btrfs/extent_map.h b/fs/btrfs/extent_map.h index 35d27c756e08..2093720271ea 100644 --- a/fs/btrfs/extent_map.h +++ b/fs/btrfs/extent_map.h @@ -55,11 +55,18 @@ struct extent_map { refcount_t refs; unsigned int compress_type; struct list_head list; + struct list_head free_list; +}; + +enum extent_map_flags { + EXTENT_MAP_TREE_PENDING_FREES, }; struct extent_map_tree { struct rb_root_cached map; + unsigned long flags; struct list_head modified_extents; + struct list_head freed_extents; rwlock_t lock; }; @@ -95,6 +102,9 @@ int split_extent_map(struct btrfs_inode *inode, u64 start, u64 len, u64 pre, struct extent_map *alloc_extent_map(void); void free_extent_map(struct extent_map *em); +void free_extent_map_safe(struct extent_map_tree *tree, + struct extent_map *em); +void free_pending_extent_maps(struct extent_map_tree *tree); int __init extent_map_init(void); void __cold extent_map_exit(void); int unpin_extent_cache(struct extent_map_tree *tree, u64 start, u64 len, u64 gen); diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c index 8b3893c01734..d3803db10939 100644 --- a/fs/btrfs/tree-log.c +++ b/fs/btrfs/tree-log.c @@ -4884,7 +4884,7 @@ static int btrfs_log_changed_extents(struct btrfs_trans_handle *trans, */ if (ret) { clear_em_logging(tree, em); - free_extent_map(em); + free_extent_map_safe(tree, em); continue; } @@ -4893,11 +4893,13 @@ static int btrfs_log_changed_extents(struct btrfs_trans_handle *trans, ret = log_one_extent(trans, inode, em, path, ctx); write_lock(&tree->lock); clear_em_logging(tree, em); - free_extent_map(em); + free_extent_map_safe(tree, em); } WARN_ON(!list_empty(&extents)); write_unlock(&tree->lock); + free_pending_extent_maps(tree); + if (!ret) ret = btrfs_log_prealloc_extents(trans, inode, path); if (ret)