linux-kernel - Re: WARNING: CPU: 1 PID: 52 at mm/page_alloc.c:4826 __alloc_pages_nodemask (Re: [PATCH 5/5] sysctl: pass kernel pointers to ->proc

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Message-ID: <20200608065120.GA17859@lst.de>
Date:   Mon, 8 Jun 2020 08:51:20 +0200
From:   Christoph Hellwig <hch@....de>
To:     Vegard Nossum <vegard.nossum@...cle.com>
Cc:     Christoph Hellwig <hch@....de>, Kees Cook <keescook@...omium.org>,
        Iurii Zaikin <yzaikin@...gle.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        linux-kernel@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>,
        bpf@...r.kernel.org, Andrey Ignatov <rdna@...com>
Subject: Re: WARNING: CPU: 1 PID: 52 at mm/page_alloc.c:4826
 __alloc_pages_nodemask (Re: [PATCH 5/5] sysctl: pass kernel
 pointers to ->proc_handler)

On Thu, Jun 04, 2020 at 10:22:21PM +0200, Vegard Nossum wrote:
> It's easy to reproduce by just doing
>
>     read(open("/proc/sys/vm/swappiness", O_RDONLY), 0, 512UL * 1024 * 1024 
> * 1024);
>
> or so. Reverting the commit fixes the issue for me.

Yes, doing giant allocations will fail and trace.  We have to options
here that both seems sensible:

 - trunate sysctrl calls to some sensible length
 - (optionally) use vmalloc

Is this a real application or just a test case trying to do the
stupidmost possible thing?