From: Filipe Manana fdmanana@suse.com
commit 76a6d5cd74479e7ec8a7f9a29bce63d5549b6b2e upstream.
There are a few cases where cloning an inline extent requires copying data into a page of the destination inode. For these cases we are allocating the required data and metadata space while holding a leaf locked. This can result in a deadlock when we are low on available space because allocating the space may flush delalloc and two deadlock scenarios can happen:
1) When starting writeback for an inode with a very small dirty range that fits in an inline extent, we deadlock during the writeback when trying to insert the inline extent, at cow_file_range_inline(), if the extent is going to be located in the leaf for which we are already holding a read lock;
2) After successfully starting writeback, for non-inline extent cases, the async reclaim thread will hang waiting for an ordered extent to complete if the ordered extent completion needs to modify the leaf for which the clone task is holding a read lock (for adding or replacing file extent items). So the cloning task will wait forever on the async reclaim thread to make progress, which in turn is waiting for the ordered extent completion which in turn is waiting to acquire a write lock on the same leaf.
So fix this by making sure we release the path (and therefore the leaf) every time we need to copy the inline extent's data into a page of the destination inode, as by that time we do not need to have the leaf locked.
Fixes: 05a5a7621ce66c ("Btrfs: implement full reflink support for inline extents") CC: stable@vger.kernel.org # 5.10+ Signed-off-by: Filipe Manana fdmanana@suse.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/btrfs/reflink.c | 38 ++++++++++++++++++++++---------------- 1 file changed, 22 insertions(+), 16 deletions(-)
--- a/fs/btrfs/reflink.c +++ b/fs/btrfs/reflink.c @@ -207,10 +207,7 @@ static int clone_copy_inline_extent(stru * inline extent's data to the page. */ ASSERT(key.offset > 0); - ret = copy_inline_to_page(BTRFS_I(dst), new_key->offset, - inline_data, size, datal, - comp_type); - goto out; + goto copy_to_page; } } else if (i_size_read(dst) <= datal) { struct btrfs_file_extent_item *ei; @@ -226,13 +223,10 @@ static int clone_copy_inline_extent(stru BTRFS_FILE_EXTENT_INLINE) goto copy_inline_extent;
- ret = copy_inline_to_page(BTRFS_I(dst), new_key->offset, - inline_data, size, datal, comp_type); - goto out; + goto copy_to_page; }
copy_inline_extent: - ret = 0; /* * We have no extent items, or we have an extent at offset 0 which may * or may not be inlined. All these cases are dealt the same way. @@ -244,11 +238,13 @@ copy_inline_extent: * clone. Deal with all these cases by copying the inline extent * data into the respective page at the destination inode. */ - ret = copy_inline_to_page(BTRFS_I(dst), new_key->offset, - inline_data, size, datal, comp_type); - goto out; + goto copy_to_page; }
+ /* + * Release path before starting a new transaction so we don't hold locks + * that would confuse lockdep. + */ btrfs_release_path(path); /* * If we end up here it means were copy the inline extent into a leaf @@ -286,11 +282,6 @@ copy_inline_extent: out: if (!ret && !trans) { /* - * Release path before starting a new transaction so we don't - * hold locks that would confuse lockdep. - */ - btrfs_release_path(path); - /* * No transaction here means we copied the inline extent into a * page of the destination inode. * @@ -310,6 +301,21 @@ out: *trans_out = trans;
return ret; + +copy_to_page: + /* + * Release our path because we don't need it anymore and also because + * copy_inline_to_page() needs to reserve data and metadata, which may + * need to flush delalloc when we are low on available space and + * therefore cause a deadlock if writeback of an inline extent needs to + * write to the same leaf or an ordered extent completion needs to write + * to the same leaf. + */ + btrfs_release_path(path); + + ret = copy_inline_to_page(BTRFS_I(dst), new_key->offset, + inline_data, size, datal, comp_type); + goto out; }
/**