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 stable@vger.kernel.org.

thanks,

greg k-h

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

From 5f0addf7b89085f8e0a2593faa419d6111612b9b Mon Sep 17 00:00:00 2001 From: Naohiro Aota naohiro.aota@wdc.com 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.

Fixes: 35156d852762 ("btrfs: zoned: only allow one process to add pages to a relocation inode") CC: stable@vger.kernel.org # 5.16.x: 869f4cdc73f9: btrfs: zoned: encapsulate inode locking for zoned relocation CC: stable@vger.kernel.org # 5.16.x CC: stable@vger.kernel.org # 5.17 Cc: Johannes Thumshirn johannes.thumshirn@wdc.com Reviewed-by: Johannes Thumshirn johannes.thumshirn@wdc.com Signed-off-by: Naohiro Aota naohiro.aota@wdc.com Signed-off-by: David Sterba dsterba@suse.com

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h index 4db17bd05a21..604a4d54cf0d 100644 --- a/fs/btrfs/ctree.h +++ b/fs/btrfs/ctree.h @@ -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;

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c index cebd7a78c964..20e70eb88465 100644 --- a/fs/btrfs/disk-io.c +++ b/fs/btrfs/disk-io.c @@ -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); diff --git a/fs/btrfs/zoned.h b/fs/btrfs/zoned.h index cbf016a7bb5d..6dee76248cb4 100644 --- a/fs/btrfs/zoned.h +++ b/fs/btrfs/zoned.h @@ -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