FAILED: patch "[PATCH] btrfs: zoned: use dedicated lock for data relocation" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 5f0addf7b89085f8e0a2593faa419d6111612b9b Mon Sep 17 00:00:00 2001
From: Naohiro Aota <[email protected]>
Date: Mon, 18 Apr 2022 16:15:03 +0900
Subject: [PATCH] btrfs: zoned: use dedicated lock for data relocation

Currently, we use btrfs_inode_{lock,unlock}() to grant an exclusive writeback of the relocation data inode in btrfs_zoned_data_reloc_{lock,unlock}(). However, that can cause a deadlock in the following path.

Thread A takes btrfs_inode_lock() and waits for metadata reservation by e.g, waiting for writeback:

prealloc_file_extent_cluster()
- btrfs_inode_lock(&inode->vfs_inode, 0);
- btrfs_prealloc_file_range()
...
- btrfs_replace_file_extents()
- btrfs_start_transaction
...
- btrfs_reserve_metadata_bytes()

Thread B (e.g, doing a writeback work) needs to wait for the inode lock to continue writeback process:

do_writepages
- btrfs_writepages
- extent_writpages
- btrfs_zoned_data_reloc_lock(BTRFS_I(inode));
- btrfs_inode_lock()

The deadlock is caused by relying on the vfs_inode's lock. By using it, we introduced unnecessary exclusion of writeback and btrfs_prealloc_file_range(). Also, the lock at this point is useless as we don't have any dirty pages in the inode yet.

Introduce fs_info->zoned_data_reloc_io_lock and use it for the exclusive writeback.

index 4db17bd05a21..604a4d54cf0d 100644
@@ -1060,6 +1060,7 @@ struct btrfs_fs_info {
 	 */
 	spinlock_t relocation_bg_lock;
 	u64 data_reloc_bg;
+	struct mutex zoned_data_reloc_io_lock;
 
 	u64 nr_global_roots;
 

index cebd7a78c964..20e70eb88465 100644
@@ -3156,6 +3156,7 @@ void btrfs_init_fs_info(struct btrfs_fs_info *fs_info)
 	mutex_init(&fs_info->reloc_mutex);
 	mutex_init(&fs_info->delalloc_root_mutex);
 	mutex_init(&fs_info->zoned_meta_io_lock);
+	mutex_init(&fs_info->zoned_data_reloc_io_lock);
 	seqlock_init(&fs_info->profiles_lock);
 
 	INIT_LIST_HEAD(&fs_info->dirty_cowonly_roots);

index cbf016a7bb5d..6dee76248cb4 100644
@@ -359,7 +359,7 @@ static inline void btrfs_zoned_data_reloc_lock(struct btrfs_inode *inode)
 	struct btrfs_root *root = inode->root;
 
 	if (btrfs_is_data_reloc_root(root) && btrfs_is_zoned(root->fs_info))
-		btrfs_inode_lock(&inode->vfs_inode, 0);
+		mutex_lock(&root->fs_info->zoned_data_reloc_io_lock);
 }
 
 static inline void btrfs_zoned_data_reloc_unlock(struct btrfs_inode *inode)

@@ -367,7 +367,7 @@ static inline void btrfs_zoned_data_reloc_unlock(struct btrfs_inode *inode)
 	struct btrfs_root *root = inode->root;
 
 	if (btrfs_is_data_reloc_root(root) && btrfs_is_zoned(root->fs_info))
-		btrfs_inode_unlock(&inode->vfs_inode, 0);
+		mutex_unlock(&root->fs_info->zoned_data_reloc_io_lock);
 }
 
 #endif