The patch titled
Subject: mm/memcontrol.c: fix potential uninitialized variable warning
has been added to the -mm tree. Its filename is
mm-memcg-optimize-user-context-object-stock-access-fix.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/mm-memcg-optimize-user-context-object-stock-access-fix.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/mm-memcg-optimize-user-context-object-stock-access-fix.patch
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------------------------------------------------------
From: Waiman Long <longman@xxxxxxxxxx>
Subject: mm/memcontrol.c: fix potential uninitialized variable warning
If the -Wno-maybe-uninitialized gcc option is not specified, compilation
of memcontrol.c may generate the following warnings:
mm/memcontrol.c: In function `refill_obj_stock':
./arch/x86/include/asm/irqflags.h:127:17: warning: `flags' may be used uninitialized in this function [-Wmaybe-uninitialized]
return !(flags & X86_EFLAGS_IF);
~~~~~~~^~~~~~~~~~~~~~~~
mm/memcontrol.c:3216:16: note: `flags' was declared here
unsigned long flags;
^~~~~
In file included from mm/memcontrol.c:29:
mm/memcontrol.c: In function `uncharge_page':
./include/linux/memcontrol.h:797:2: warning: `objcg' may be used uninitialized in this function [-Wmaybe-uninitialized]
percpu_ref_put(&objcg->refcnt);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Fix that by properly initializing *pflags in get_obj_stock() and
introducing a use_objcg bool variable in uncharge_page() to avoid
potentially accessing the struct page data twice.
Link: https://lkml.kernel.org/r/20210526193602.8742-1-longman@xxxxxxxxxx
Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
Cc: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memcontrol.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
--- a/mm/memcontrol.c~mm-memcg-optimize-user-context-object-stock-access-fix
+++ a/mm/memcontrol.c
@@ -2115,6 +2115,7 @@ static inline struct obj_stock *get_obj_
struct memcg_stock_pcp *stock;
if (likely(in_task())) {
+ *pflags = 0UL;
preempt_disable();
stock = this_cpu_ptr(&memcg_stock);
return &stock->task_obj;
@@ -6832,6 +6833,7 @@ static void uncharge_page(struct page *p
unsigned long nr_pages;
struct mem_cgroup *memcg;
struct obj_cgroup *objcg;
+ bool use_objcg = PageMemcgKmem(page);
VM_BUG_ON_PAGE(PageLRU(page), page);
@@ -6840,7 +6842,7 @@ static void uncharge_page(struct page *p
* page memcg or objcg at this point, we have fully
* exclusive access to the page.
*/
- if (PageMemcgKmem(page)) {
+ if (use_objcg) {
objcg = __page_objcg(page);
/*
* This get matches the put at the end of the function and
@@ -6868,7 +6870,7 @@ static void uncharge_page(struct page *p
nr_pages = compound_nr(page);
- if (PageMemcgKmem(page)) {
+ if (use_objcg) {
ug->nr_memory += nr_pages;
ug->nr_kmem += nr_pages;
_
Patches currently in -mm which might be from longman@xxxxxxxxxx are
mm-memcg-move-mod_objcg_state-to-memcontrolc.patch
mm-memcg-cache-vmstat-data-in-percpu-memcg_stock_pcp.patch
mm-memcg-improve-refill_obj_stock-performance.patch
mm-memcg-optimize-user-context-object-stock-access.patch
mm-memcg-optimize-user-context-object-stock-access-fix.patch
mm-memcg-slab-properly-set-up-gfp-flags-for-objcg-pointer-array.patch
mm-memcg-slab-create-a-new-set-of-kmalloc-cg-n-caches.patch
mm-memcg-slab-create-a-new-set-of-kmalloc-cg-n-caches-v5.patch
mm-memcg-slab-disable-cache-merging-for-kmalloc_normal-caches.patch
