On 5/26/21 4:43 PM, Andrew Morton wrote:

On Wed, 26 May 2021 15:36:02 -0400 Waiman Long [off-list ref] wrote:

quoted

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.

Thanks.  I'll queue this as a fix against your "mm/memcg: optimize user
context object stock access".

Thanks for that.

Cheers,
Longman