Re: fs/buffer.c: WARNING: alloc_page_buffers while mke2fs

[Shakeel Butt <shakeelb@google.com>]

On Tue, Mar 3, 2020 at 9:47 AM Yang Shi <shy828301@gmail.com> wrote:
>
> On Tue, Mar 3, 2020 at 2:53 AM Tetsuo Handa
> <penguin-kernel@i-love.sakura.ne.jp> 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.