Btrfs: fix race deleting block group from space_info->ro_bgs list (75c68e9f) · Commits · 戴 / test

When removing a block group we were deleting it from its space_info's ro_bgs list without the correct protection - the space info's spinlock. Fix this by doing the list delete while holding the spinlock of the corresponding space info, which is the correct lock for any operation on that list. This issue was introduced in the 3.19 kernel by the following change: Btrfs: move read only block groups onto their own list V2 commit I ran into a kernel crash while a task was running statfs, which iterates the space_info->ro_bgs list while holding the space info's spinlock, and another task was deleting it from the same list, without holding that spinlock, as part of the block group remove operation (while running the function btrfs_remove_block_group). This happened often when running the stress test xfstests/generic/038 I recently made. Signed-off-by:

Filipe Manana <fdmanana@suse.com> Signed-off-by:

Chris Mason <clm@fb.com>

fs/btrfs/ctree.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -1171,6 +1171,7 @@ struct btrfs_space_info {
		struct percpu_counter total_bytes_pinned;

		struct list_head list;
		/* Protected by the spinlock 'lock'. */
		struct list_head ro_bgs;

		struct rw_semaphore groups_sem;

fs/btrfs/extent-tree.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -9422,7 +9422,6 @@ int btrfs_remove_block_group(struct btrfs_trans_handle *trans,
		* are still on the list after taking the semaphore
		*/
		list_del_init(&block_group->list);
		list_del_init(&block_group->ro_list);
		if (list_empty(&block_group->space_info->block_groups[index])) {
		kobj = block_group->space_info->block_group_kobjs[index];
		block_group->space_info->block_group_kobjs[index] = NULL;
		@@ -9464,6 +9463,7 @@ int btrfs_remove_block_group(struct btrfs_trans_handle *trans,
		btrfs_remove_free_space_cache(block_group);

		spin_lock(&block_group->space_info->lock);
		list_del_init(&block_group->ro_list);
		block_group->space_info->total_bytes -= block_group->key.offset;
		block_group->space_info->bytes_readonly -= block_group->key.offset;
		block_group->space_info->disk_total -= block_group->key.offset * factor;

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