Commit 39ad3173 authored Mar 26, 2019 by Robbie Ko Committed by David Sterba Apr 29, 2019

Btrfs: fix data bytes_may_use underflow with fallocate due to failed quota reserve



When doing fallocate, we first add the range to the reserve_list and
then reserve the quota.  If quota reservation fails, we'll release all
reserved parts of reserve_list.

However, cur_offset is not updated to indicate that this range is
already been inserted into the list.  Therefore, the same range is freed
twice.  Once at list_for_each_entry loop, and once at the end of the
function.  This will result in WARN_ON on bytes_may_use when we free the
remaining space.

At the end, under the 'out' label we have a call to:

   btrfs_free_reserved_data_space(inode, data_reserved, alloc_start, alloc_end - cur_offset);

The start offset, third argument, should be cur_offset.

Everything from alloc_start to cur_offset was freed by the
list_for_each_entry_safe_loop.

Fixes: 18513091 ("btrfs: update btrfs_space_info's bytes_may_use timely")
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Robbie Ko <robbieko@synology.com>
Signed-off-by: David Sterba <dsterba@suse.com>

parent 17850759

fs/btrfs/file.c

+2 −1

Original line number	Diff line number	Diff line
		@@ -3131,6 +3131,7 @@ static long btrfs_fallocate(struct file *file, int mode,
		ret = btrfs_qgroup_reserve_data(inode, &data_reserved,
		cur_offset, last_byte - cur_offset);
		if (ret < 0) {
		cur_offset = last_byte;
		free_extent_map(em);
		break;
		}
		@@ -3180,7 +3181,7 @@ out:
		/* Let go of our reservation. */
		if (ret != 0 && !(mode & FALLOC_FL_ZERO_RANGE))
		btrfs_free_reserved_data_space(inode, data_reserved,
		alloc_start, alloc_end - cur_offset);
		cur_offset, alloc_end - cur_offset);
		extent_changeset_free(data_reserved);
		return ret;
		}

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