Btrfs: fix ENOSPC errors, leading to transaction aborts, when cloning extents

When cloning extents (or deduplicating) we create a transaction with a
space reservation that considers we will drop or update a single file
extent item of the destination inode (that we modify a single leaf). That
is fine for the vast majority of scenarios, however it might happen that
we need to drop many file extent items, and adjust at most two file extent
items, in the destination root, which can span multiple leafs. This will
lead to either the call to btrfs_drop_extents() to fail with ENOSPC or
the subsequent calls to btrfs_insert_empty_item() or btrfs_update_inode()
(called through clone_finish_inode_update()) to fail with ENOSPC. Such
failure results in a transaction abort, leaving the filesystem in a
read-only mode.

In order to fix this we need to follow the same approach as the hole
punching code, where we create a local reservation with 1 unit and keep
ending and starting transactions, after balancing the btree inode,
when __btrfs_drop_extents() returns ENOSPC. So fix this by making the
extent cloning call calls the recently added btrfs_punch_hole_range()
helper, which is what does the mentioned work for hole punching, and
make sure whenever we drop extent items in a transaction, we also add a
replacing file extent item, to avoid corruption (a hole) if after ending
a transaction and before starting a new one, the old transaction gets
committed and a power failure happens before we finish cloning.

A test case for fstests follows soon.

Reported-by: David Goodwin <david@codepoets.co.uk>
Link: https://lore.kernel.org/linux-btrfs/a4a4cf31-9cf4-e52c-1f86-c62d336c9cd1@codepoets.co.uk/
Reported-by: Sam Tygier <sam@tygier.co.uk>
Link: https://lore.kernel.org/linux-btrfs/82aace9f-a1e3-1f0b-055f-3ea75f7a41a0@tygier.co.uk/
Fixes: b6f3409b2197e8f ("Btrfs: reserve sufficient space for ioctl clone")
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 14 insertions, 0 deletions

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 94660063a162..670973025048 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1279,6 +1279,16 @@ struct btrfs_root {
 #endif
 };
 
+struct btrfs_clone_extent_info {
+	u64 disk_offset;
+	u64 disk_len;
+	u64 data_offset;
+	u64 data_len;
+	u64 file_offset;
+	char *extent_buf;
+	u32 item_size;
+};
+
 struct btrfs_file_private {
 	void *filldir_buf;
 };
@@ -3233,6 +3243,10 @@ int __btrfs_drop_extents(struct btrfs_trans_handle *trans,
 int btrfs_drop_extents(struct btrfs_trans_handle *trans,
 		       struct btrfs_root *root, struct inode *inode, u64 start,
 		       u64 end, int drop_cache);
+int btrfs_punch_hole_range(struct inode *inode, struct btrfs_path *path,
+			   const u64 start, const u64 end,
+			   struct btrfs_clone_extent_info *clone_info,
+			   struct btrfs_trans_handle **trans_out);
 int btrfs_mark_extent_written(struct btrfs_trans_handle *trans,
 			      struct btrfs_inode *inode, u64 start, u64 end);
 int btrfs_release_file(struct inode *inode, struct file *file);