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.
