[PATCH] btrfs: reloc: clear DEAD_RELOC_TREE bit for orphan roots to prevent runaway balance

[PATCH] btrfs: reloc: clear DEAD_RELOC_TREE bit for orphan roots to prevent runaway balance

[Qu Wenruo]

commit 1dae7e0e58b484eaa43d530f211098fdeeb0f404 upstream.

[BUG]
There are several reported runaway balance, that balance is flooding the
log with "found X extents" where the X never changes.

[CAUSE]
Commit d2311e698578 ("btrfs: relocation: Delay reloc tree deletion after
merge_reloc_roots") introduced BTRFS_ROOT_DEAD_RELOC_TREE bit to
indicate that one subvolume has finished its tree blocks swap with its
reloc tree.

However if balance is canceled or hits ENOSPC halfway, we didn't clear
the BTRFS_ROOT_DEAD_RELOC_TREE bit, leaving that bit hanging forever
until unmount.

Any subvolume root with that bit, would cause backref cache to skip this
tree block, as it has finished its tree block swap.  This would cause
all tree blocks of that root be ignored by balance, leading to runaway
balance.

[FIX]
Fix the problem by also clearing the BTRFS_ROOT_DEAD_RELOC_TREE bit for
the original subvolume of orphan reloc root.

Add an umount check for the stale bit still set.

Fixes: d2311e698578 ("btrfs: relocation: Delay reloc tree deletion after merge_reloc_roots")
Cc: <stable@vger.kernel.org> # 5.7.x
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
---
 fs/btrfs/disk-io.c    | 1 +
 fs/btrfs/relocation.c | 2 ++
 2 files changed, 3 insertions(+)

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index f71e4dbe1d8a..f00e64fee5dd 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1998,6 +1998,7 @@ void btrfs_put_root(struct btrfs_root *root)
 
 	if (refcount_dec_and_test(&root->refs)) {
 		WARN_ON(!RB_EMPTY_ROOT(&root->inode_tree));
+		WARN_ON(test_bit(BTRFS_ROOT_DEAD_RELOC_TREE, &root->state));
 		if (root->anon_dev)
 			free_anon_bdev(root->anon_dev);
 		btrfs_drew_lock_destroy(&root->snapshot_lock);
diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index 157452a5e110..f67d736c27a1 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -2642,6 +2642,8 @@ void merge_reloc_roots(struct reloc_control *rc)
 					root->reloc_root = NULL;
 					btrfs_put_root(reloc_root);
 				}
+				clear_bit(BTRFS_ROOT_DEAD_RELOC_TREE,
+					  &root->state);
 				btrfs_put_root(root);
 			}
 
-- 
2.27.0

Re: [PATCH] btrfs: reloc: clear DEAD_RELOC_TREE bit for orphan roots -- for 5.7 to prevent runaway balance

[David Sterba]

Qu,

you need to make the target version visible in the subject. The manual
submissions to stable are processed by humans, while the CC: tag is for
semi-automatic collection of patches that get merged to master.

If you send 3 patches with same subjects it could be ignored as resends
or it's required to read all the changelogs.

On Fri, Jul 24, 2020 at 09:46:40AM +0800, Qu Wenruo wrote:
> commit 1dae7e0e58b484eaa43d530f211098fdeeb0f404 upstream.
> 
> [BUG]
> There are several reported runaway balance, that balance is flooding the
> log with "found X extents" where the X never changes.
> 
> [CAUSE]
> Commit d2311e698578 ("btrfs: relocation: Delay reloc tree deletion after
> merge_reloc_roots") introduced BTRFS_ROOT_DEAD_RELOC_TREE bit to
> indicate that one subvolume has finished its tree blocks swap with its
> reloc tree.
> 
> However if balance is canceled or hits ENOSPC halfway, we didn't clear
> the BTRFS_ROOT_DEAD_RELOC_TREE bit, leaving that bit hanging forever
> until unmount.
> 
> Any subvolume root with that bit, would cause backref cache to skip this
> tree block, as it has finished its tree block swap.  This would cause
> all tree blocks of that root be ignored by balance, leading to runaway
> balance.
> 
> [FIX]
> Fix the problem by also clearing the BTRFS_ROOT_DEAD_RELOC_TREE bit for
> the original subvolume of orphan reloc root.
> 
> Add an umount check for the stale bit still set.
> 
> Fixes: d2311e698578 ("btrfs: relocation: Delay reloc tree deletion after merge_reloc_roots")
> Cc: <stable@vger.kernel.org> # 5.7.x
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> Signed-off-by: David Sterba <dsterba@suse.com>
> ---
>  fs/btrfs/disk-io.c    | 1 +
>  fs/btrfs/relocation.c | 2 ++
>  2 files changed, 3 insertions(+)
> 
> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
> index f71e4dbe1d8a..f00e64fee5dd 100644
> --- a/fs/btrfs/disk-io.c
> +++ b/fs/btrfs/disk-io.c
> @@ -1998,6 +1998,7 @@ void btrfs_put_root(struct btrfs_root *root)
>  
>  	if (refcount_dec_and_test(&root->refs)) {
>  		WARN_ON(!RB_EMPTY_ROOT(&root->inode_tree));
> +		WARN_ON(test_bit(BTRFS_ROOT_DEAD_RELOC_TREE, &root->state));
>  		if (root->anon_dev)
>  			free_anon_bdev(root->anon_dev);
>  		btrfs_drew_lock_destroy(&root->snapshot_lock);
> diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
> index 157452a5e110..f67d736c27a1 100644
> --- a/fs/btrfs/relocation.c
> +++ b/fs/btrfs/relocation.c
> @@ -2642,6 +2642,8 @@ void merge_reloc_roots(struct reloc_control *rc)
>  					root->reloc_root = NULL;
>  					btrfs_put_root(reloc_root);
>  				}
> +				clear_bit(BTRFS_ROOT_DEAD_RELOC_TREE,
> +					  &root->state);
>  				btrfs_put_root(root);
>  			}
>  
> -- 
> 2.27.0

Re: [PATCH] btrfs: reloc: clear DEAD_RELOC_TREE bit for orphan roots to prevent runaway balance

[Greg KH]

On Fri, Jul 24, 2020 at 09:46:40AM +0800, Qu Wenruo wrote:
> commit 1dae7e0e58b484eaa43d530f211098fdeeb0f404 upstream.
> 
> [BUG]
> There are several reported runaway balance, that balance is flooding the
> log with "found X extents" where the X never changes.
> 
> [CAUSE]
> Commit d2311e698578 ("btrfs: relocation: Delay reloc tree deletion after
> merge_reloc_roots") introduced BTRFS_ROOT_DEAD_RELOC_TREE bit to
> indicate that one subvolume has finished its tree blocks swap with its
> reloc tree.
> 
> However if balance is canceled or hits ENOSPC halfway, we didn't clear
> the BTRFS_ROOT_DEAD_RELOC_TREE bit, leaving that bit hanging forever
> until unmount.
> 
> Any subvolume root with that bit, would cause backref cache to skip this
> tree block, as it has finished its tree block swap.  This would cause
> all tree blocks of that root be ignored by balance, leading to runaway
> balance.
> 
> [FIX]
> Fix the problem by also clearing the BTRFS_ROOT_DEAD_RELOC_TREE bit for
> the original subvolume of orphan reloc root.
> 
> Add an umount check for the stale bit still set.
> 
> Fixes: d2311e698578 ("btrfs: relocation: Delay reloc tree deletion after merge_reloc_roots")
> Cc: <stable@vger.kernel.org> # 5.7.x
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> Signed-off-by: David Sterba <dsterba@suse.com>
> ---
>  fs/btrfs/disk-io.c    | 1 +
>  fs/btrfs/relocation.c | 2 ++
>  2 files changed, 3 insertions(+)

Thanks for the backports, all now queued up.

greg k-h