On Tue, Mar 3, 2020 at 11:42 AM Yang Shi <shy828301@xxxxxxxxx> wrote:
>
> On Tue, Mar 3, 2020 at 10:15 AM Shakeel Butt <shakeelb@xxxxxxxxxx> wrote:
> >
> > On Tue, Mar 3, 2020 at 9:47 AM Yang Shi <shy828301@xxxxxxxxx> wrote:
> > >
> > > On Tue, Mar 3, 2020 at 2:53 AM Tetsuo Handa
> > > <penguin-kernel@xxxxxxxxxxxxxxxxxxx> wrote:
> > > >
> > > > Hello, Naresh.
> > > >
> > > > > [ 98.003346] WARNING: CPU: 2 PID: 340 at
> > > > > include/linux/sched/mm.h:323 alloc_page_buffers+0x210/0x288
> > > >
> > > > This is
> > > >
> > > > /**
> > > > * memalloc_use_memcg - Starts the remote memcg charging scope.
> > > > * @memcg: memcg to charge.
> > > > *
> > > > * This function marks the beginning of the remote memcg charging scope. All the
> > > > * __GFP_ACCOUNT allocations till the end of the scope will be charged to the
> > > > * given memcg.
> > > > *
> > > > * NOTE: This function is not nesting safe.
> > > > */
> > > > static inline void memalloc_use_memcg(struct mem_cgroup *memcg)
> > > > {
> > > > WARN_ON_ONCE(current->active_memcg);
> > > > current->active_memcg = memcg;
> > > > }
> > > >
> > > > which is about memcg. Redirecting to linux-mm.
> > >
> > > Isn't this triggered by ("loop: use worker per cgroup instead of
> > > kworker") in linux-next, which converted loop driver to use worker per
> > > cgroup, so it may have multiple workers work at the mean time?
> > >
> > > So they may share the same "current", then it may cause kind of nested
> > > call to memalloc_use_memcg().
> > >
> > > Could you please try the below debug patch? This is not the proper
> > > fix, but it may help us narrow down the problem.
> > >
> > > diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
> > > index c49257a..1cc1cdc 100644
> > > --- a/include/linux/sched/mm.h
> > > +++ b/include/linux/sched/mm.h
> > > @@ -320,6 +320,10 @@ static inline void
> > > memalloc_nocma_restore(unsigned int flags)
> > > */
> > > static inline void memalloc_use_memcg(struct mem_cgroup *memcg)
> > > {
> > > + if ((current->flags & PF_KTHREAD) &&
> > > + current->active_memcg)
> > > + return;
> > > +
> > > WARN_ON_ONCE(current->active_memcg);
> > > current->active_memcg = memcg;
> > > }
> > >
> >
> > Maybe it's time to make memalloc_use_memcg() nesting safe.
>
> Need handle the below case:
>
> CPU A CPU B
> memalloc_use_memcg
> memalloc_use_memcg
> memalloc_unuse_memcg
> memalloc_unuse_memcg
>
>
> They may manipulate the same task->active_memcg, so CPU B may still
> see wrong memcg, and the last call to memalloc_unuse_memcg() on CPU B
> may not restore active_memcg to NULL. And, some code depends on
> correct active_memcg.
Sorry for asking a simple question. What does it mean that more than
one kworkers share the same 'current'?
