linux-kernel - Re: powertop "pread cpu0 0xe8 : Bad file descriptor" fixed by CONFIG

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Date:	Mon, 8 Aug 2011 17:08:07 +0800
From:	Américo Wang <xiyou.wangcong@...il.com>
To:	Andy Isaacson <adi@...apodia.org>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: powertop "pread cpu0 0xe8 : Bad file descriptor" fixed by CONFIG_MSR

On Sun, Aug 7, 2011 at 6:52 AM, Andy Isaacson <adi@...apodia.org> wrote:
> I hadn't seen this issue discussed on the list, and I don't know of a
> powertop mailing list, so here's what stymied my use of powertop until I
> straced it.
>
> With CONFIG_MSR=n, powertop "1.97-2" (from Debian unstable) on 3.0.1
> (and presumably many other recent kernels) exits at startup with:
>
> pread cpu0 0xe8 : Bad file descriptor
>
> strace shows:
>
> open("/dev/cpu/0/msr", O_RDONLY) = -1 ENOENT (No such file or directory)
> pread(4294967295, 0x7fff4c8347c8, 8, 232) = -1 EBADF (Bad file descriptor)
>

Seems powertop forgot to check the return value of that open().
This is a bug of powertop, not kernel.
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