In the Linux kernel, the following vulnerability has been resolved:

btrfs: fix reloc root cleanup in merge reloc roots()

If the root we got has zero root refs in its root item, we are resetting the root's ->reloc root without using barriers like we do everywhere else. Sashiko complained about this while reviewing another patch, and it's correct (see the Link tag below).

Also, we should not clear BTRFS ROOT DEAD RELOC TREE from the root unless the root points to the reloc root we have.

Fix this by using clear reloc root(), which issues the memory barrier after setting the root's ->reloc root to NULL and before clearing the bit BTRFS ROOT DEAD RELOC TREE from the root.