The patch titled
Subject: lib/alloc_tag: fix RCU imbalance in pgalloc_tag_get()
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
lib-alloc_tag-fix-rcu-imbalance-in-pgalloc_tag_get.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/lib-alloc_tag-fix-rcu-imbalance-in-pgalloc_tag_get.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Subject: lib/alloc_tag: fix RCU imbalance in pgalloc_tag_get()
Date: Sat, 1 Jun 2024 16:38:40 -0700
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@xxxxxxxxxx
Fixes: cc92eba1c88b ("mm: fix non-compound multi-order memory accounting in __free_pages")
Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
Closes: https://lore.kernel.org/oe-lkp/202405271029.6d2f9c4c-lkp@xxxxxxxxx
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Kent Overstreet <kent.overstreet@xxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/pgalloc_tag.h | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)
--- a/include/linux/pgalloc_tag.h~lib-alloc_tag-fix-rcu-imbalance-in-pgalloc_tag_get
+++ a/include/linux/pgalloc_tag.h
@@ -37,6 +37,9 @@ static inline union codetag_ref *get_pag
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));
}
@@ -102,9 +105,11 @@ static inline struct alloc_tag *pgalloc_
union codetag_ref *ref = get_page_tag_ref(page);
alloc_tag_sub_check(ref);
- if (ref && ref->ct)
- tag = ct_to_alloc_tag(ref->ct);
- put_page_tag_ref(ref);
+ if (ref) {
+ if (ref->ct)
+ tag = ct_to_alloc_tag(ref->ct);
+ put_page_tag_ref(ref);
+ }
}
return tag;
_
Patches currently in -mm which might be from surenb@xxxxxxxxxx are
mm-fix-xyz_noprof-functions-calling-profiled-functions.patch
lib-alloc_tag-fix-rcu-imbalance-in-pgalloc_tag_get.patch
