| Message ID | 6cf44f7860e94de68df242e69f4c5250bd061cff.1706116485.git.josef@toxicpanda.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | btrfs: add fscrypt support | expand |
On Wed, Jan 24, 2024 at 12:18:31PM -0500, Josef Bacik wrote: > 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 <josef@toxicpanda.com> Reviewed-by: Boris Burkov <boris@bur.io> > --- > fs/btrfs/extent_map.c | 76 +++++++++++++++++++++++++++++++++++++++++-- > fs/btrfs/extent_map.h | 10 ++++++ > fs/btrfs/tree-log.c | 6 ++-- > 3 files changed, 87 insertions(+), 5 deletions(-) > > diff --git a/fs/btrfs/extent_map.c b/fs/btrfs/extent_map.c > index b61099bf97a8..f8705103819c 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); > } > > @@ -52,9 +54,15 @@ struct extent_map *alloc_extent_map(void) > RB_CLEAR_NODE(&em->rb_node); > 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) > +{ > + 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. > @@ -66,10 +74,69 @@ 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)); > - 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)); I'm pretty convinced that the refcount properly protects the rb_node path as well, but I think a WARN/ASSERT on that wouldn't hurt either, now that we are adding this deferred unlocked freeing. > + 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) > { > @@ -654,10 +721,12 @@ static void drop_all_extent_maps_fast(struct extent_map_tree *tree) > em = rb_entry(node, struct extent_map, rb_node); > em->flags &= ~(EXTENT_FLAG_PINNED | EXTENT_FLAG_LOGGING); > 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); > } > > /* > @@ -875,13 +944,14 @@ 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 e380fc08bbe4..d31f2a03670e 100644 > --- a/fs/btrfs/extent_map.h > +++ b/fs/btrfs/extent_map.h > @@ -55,11 +55,18 @@ struct extent_map { > u32 flags; > refcount_t refs; > 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; > }; > > @@ -122,6 +129,9 @@ 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 btrfs_inode *inode, u64 start, u64 len, u64 gen); > diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c > index 331fc7429952..916e54b91ecc 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) > -- > 2.43.0 >
diff --git a/fs/btrfs/extent_map.c b/fs/btrfs/extent_map.c index b61099bf97a8..f8705103819c 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); } @@ -52,9 +54,15 @@ struct extent_map *alloc_extent_map(void) RB_CLEAR_NODE(&em->rb_node); 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) +{ + 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. @@ -66,10 +74,69 @@ 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)); - 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) { @@ -654,10 +721,12 @@ static void drop_all_extent_maps_fast(struct extent_map_tree *tree) em = rb_entry(node, struct extent_map, rb_node); em->flags &= ~(EXTENT_FLAG_PINNED | EXTENT_FLAG_LOGGING); 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); } /* @@ -875,13 +944,14 @@ 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 e380fc08bbe4..d31f2a03670e 100644 --- a/fs/btrfs/extent_map.h +++ b/fs/btrfs/extent_map.h @@ -55,11 +55,18 @@ struct extent_map { u32 flags; refcount_t refs; 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; }; @@ -122,6 +129,9 @@ 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 btrfs_inode *inode, u64 start, u64 len, u64 gen); diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c index 331fc7429952..916e54b91ecc 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)
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 <josef@toxicpanda.com> --- fs/btrfs/extent_map.c | 76 +++++++++++++++++++++++++++++++++++++++++-- fs/btrfs/extent_map.h | 10 ++++++ fs/btrfs/tree-log.c | 6 ++-- 3 files changed, 87 insertions(+), 5 deletions(-)