Commit a273559e authored Jun 01, 2024 by Suren Baghdasaryan Committed by Andrew Morton Jun 15, 2024

lib/alloc_tag: fix RCU imbalance in pgalloc_tag_get()

put_page_tag_ref() should be called only when get_page_tag_ref() returns a
valid reference because only in that case get_page_tag_ref() enters RCU
read section while put_page_tag_ref() will call rcu_read_unlock() even if
the provided reference is NULL.  Fix pgalloc_tag_get() which does not
follow this rule causing RCU imbalance.  Add a warning in
put_page_tag_ref() to catch any future mistakes.

Link: https://lkml.kernel.org/r/20240601233840.617458-1-surenb@google.com


Fixes: cc92eba1 ("mm: fix non-compound multi-order memory accounting in __free_pages")
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202405271029.6d2f9c4c-lkp@intel.com


Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: Kees Cook <keescook@chromium.org>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

parent c944bf60

include/linux/pgalloc_tag.h

+8 −3

Original line number	Diff line number	Diff line
		@@ -37,6 +37,9 @@ static inline union codetag_ref get_page_tag_ref(struct page page)

		static inline void put_page_tag_ref(union codetag_ref *ref)
		{
		if (WARN_ON(!ref))
		return;

		page_ext_put(page_ext_from_codetag_ref(ref));
		}

		@@ -102,10 +105,12 @@ static inline struct alloc_tag pgalloc_tag_get(struct page page)
		union codetag_ref *ref = get_page_tag_ref(page);

		alloc_tag_sub_check(ref);
		if (ref && ref->ct)
		if (ref) {
		if (ref->ct)
		tag = ct_to_alloc_tag(ref->ct);
		put_page_tag_ref(ref);
		}
		}

		return tag;
		}