linux-kernel - Re: [next] arm64: allmodconfig: kernel BUG at include/linux/page-flags.h:509

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Date:   Fri, 11 Mar 2022 15:47:15 -0800
From:   Beau Belgrave <beaub@...ux.microsoft.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Anders Roxell <anders.roxell@...aro.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux-Next Mailing List <linux-next@...r.kernel.org>,
        linux-trace-devel@...r.kernel.org
Subject: Re: [next] arm64: allmodconfig: kernel BUG at
 include/linux/page-flags.h:509

On Fri, Mar 11, 2022 at 06:36:07PM -0500, Steven Rostedt wrote:
> On Fri, 11 Mar 2022 15:28:09 -0800
> Beau Belgrave <beaub@...ux.microsoft.com> wrote:
> 
> > OK, you know more than I, so hopefully we can land on if we really need
> > it or not. For now I've left it in.
> > 
> > > > 
> > > > The other thing is that this patch applied to 5.10.X on ARM64 does not
> > > > appear to hit this. Is it some weird interaction with something else or
> > > > was 5.10.X just getting lucky?  
> > > 
> > > Perhaps it's because you allocated the page with kzalloc and not just
> > > getting a page directly?
> 
> I sent a version that removes it, but I think we can add it back.
> 
> > >   
> > 
> > Yeah, I think so too. I was able to repro locally and validate that using
> > alloc_pages directly fixes this by setting DEBUG_VM_PGFLAGS=y.
> > 
> > I've posted a patch for this:
> > https://lore.kernel.org/linux-trace-devel/20220311223028.1865-1-beaub@linux.microsoft.com/
> 
> Just saw it (I screwed up my procmail settings getting rid of some more
> spam, and ended up sending all my email to a ":" folder :-p)
> 
> If you want, I can send another version of my patch that doesn't remove the
> reserve. But I like my patch as it sets the MAX_EVENTS based on a order and
> not the other way around.

I never pass up free work (or drinks), I would prefer to keep the reserve
in there. Worst case it's redundant, best case it protects us from a
crash in a user process down the road.

Thanks,
-Beau