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

[Yang Shi <shy828301@gmail.com>]

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;
 }

>
> Please include exact backtrace extracted from scripts/faddr2line .
>
>