Btrfs: lock the transition from dirty to writeback for an eb (51561ffe) · Commits · 戴 / test

There is a small window where an eb can have no IO bits set on it, which could potentially result in extent_buffer_under_io() returning false when we want it to return true, which could result in not fun things happening. So in order to protect this case we need to hold the refs_lock when we make this transition to make sure we get reliable results out of extent_buffer_udner_io(). Thanks, Signed-off-by:

Josef Bacik <jbacik@fusionio.com>

fs/btrfs/extent_io.c

+9 −0

Original line number	Diff line number	Diff line
		@@ -3077,8 +3077,15 @@ static int lock_extent_buffer_for_io(struct extent_buffer *eb,
		}
		}

		/*
		* We need to do this to prevent races in people who check if the eb is
		* under IO since we can end up having no IO bits set for a short period
		* of time.
		*/
		spin_lock(&eb->refs_lock);
		if (test_and_clear_bit(EXTENT_BUFFER_DIRTY, &eb->bflags)) {
		set_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags);
		spin_unlock(&eb->refs_lock);
		btrfs_set_header_flag(eb, BTRFS_HEADER_FLAG_WRITTEN);
		spin_lock(&fs_info->delalloc_lock);
		if (fs_info->dirty_metadata_bytes >= eb->len)
		@@ -3087,6 +3094,8 @@ static int lock_extent_buffer_for_io(struct extent_buffer *eb,
		WARN_ON(1);
		spin_unlock(&fs_info->delalloc_lock);
		ret = 1;
		} else {
		spin_unlock(&eb->refs_lock);
		}

		btrfs_tree_unlock(eb);

Admin message