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Date:   Mon, 8 Jun 2020 08:51:20 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Vegard Nossum <vegard.nossum@oracle.com>
Cc:     Christoph Hellwig <hch@lst.de>, Kees Cook <keescook@chromium.org>,
        Iurii Zaikin <yzaikin@google.com>,
        Alexei Starovoitov <ast@kernel.org>,
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        linux-kernel@vger.kernel.org, Al Viro <viro@zeniv.linux.org.uk>,
        bpf@vger.kernel.org, Andrey Ignatov <rdna@fb.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)
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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?