| Message ID | 20240601233840.617458-1-surenb@google.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [1/1] lib/alloc_tag: fix RCU imbalance in pgalloc_tag_get() | expand |
On 6/2/24 1:38 AM, Suren Baghdasaryan wrote: > 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. > > Fixes: cc92eba1c88b ("mm: fix non-compound multi-order memory accounting in __free_pages") > Reported-by: kernel test robot <oliver.sang@intel.com> > Closes: https://lore.kernel.org/oe-lkp/202405271029.6d2f9c4c-lkp@intel.com > Signed-off-by: Suren Baghdasaryan <surenb@google.com> > Cc: Kent Overstreet <kent.overstreet@linux.dev> Acked-by: Vlastimil Babka <vbabka@suse.cz> > --- > include/linux/pgalloc_tag.h | 11 ++++++++--- > 1 file changed, 8 insertions(+), 3 deletions(-) > > diff --git a/include/linux/pgalloc_tag.h b/include/linux/pgalloc_tag.h > index 86ba5d33e43b..9cacadbd61f8 100644 > --- a/include/linux/pgalloc_tag.h > +++ b/include/linux/pgalloc_tag.h > @@ -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)); > } > > @@ -102,9 +105,11 @@ 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) > - 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; > > base-commit: 065d3634d60843b8e338d405b844cc7f2e5e1c66
diff --git a/include/linux/pgalloc_tag.h b/include/linux/pgalloc_tag.h index 86ba5d33e43b..9cacadbd61f8 100644 --- a/include/linux/pgalloc_tag.h +++ b/include/linux/pgalloc_tag.h @@ -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)); } @@ -102,9 +105,11 @@ 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) - 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;
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. Fixes: cc92eba1c88b ("mm: fix non-compound multi-order memory accounting in __free_pages") Reported-by: kernel test robot <oliver.sang@intel.com> Closes: https://lore.kernel.org/oe-lkp/202405271029.6d2f9c4c-lkp@intel.com Signed-off-by: Suren Baghdasaryan <surenb@google.com> Cc: Kent Overstreet <kent.overstreet@linux.dev> --- include/linux/pgalloc_tag.h | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) base-commit: 065d3634d60843b8e338d405b844cc7f2e5e1c66