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

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Date:   Fri, 11 Mar 2022 18:15:00 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Beau Belgrave <beaub@...ux.microsoft.com>
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, 11 Mar 2022 10:13:28 -0800
Beau Belgrave <beaub@...ux.microsoft.com> wrote:

> Is that true as well for the user process that has this mapped? Will the
> user process virtual memory that maps to this ever page it out? I
> believe that was the concern. My understanding is by reserving in
> kernel, even though it won't page out on that side, marks the user side
> entry to not let it page out.

My memory of the purpose of SetPageReserve() is a bit fuzzy, and there's
not much use of it in the kernel. Just a hand full. I'll try to investigate
it some more.

> 
> 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?

Again, my knowledge in this area is lacking. I'm looking more into it.

-- Steve