linux-kernel - Re: [2.6.37-rc1] /proc/vmstat failure.

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Message-ID: <20101104025251.GA5210@cr0.nay.redhat.com>
Date:	Thu, 4 Nov 2010 10:52:51 +0800
From:	Américo Wang <xiyou.wangcong@...il.com>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	"mrubin@...gle.com" <mrubin@...gle.com>,
	"david@...morbit.com" <david@...morbit.com>,
	"axboe@...nel.dk" <axboe@...nel.dk>,
	"kosaki.motohiro@...fujitsu.com" <kosaki.motohiro@...fujitsu.com>,
	"nickpiggin@...oo.com.au" <nickpiggin@...oo.com.au>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [2.6.37-rc1] /proc/vmstat failure.

On Thu, Nov 04, 2010 at 10:20:52AM +0800, Wu Fengguang wrote:
>On Thu, Nov 04, 2010 at 05:54:48AM +0800, Tetsuo Handa wrote:
>> Wu Fengguang wrote:
>> > On Wed, Nov 03, 2010 at 07:11:11PM +0800, Tetsuo Handa wrote:
>> > > Hello.
>> > > 
>> > > "cat /proc/vmstat" triggered below failure.
>> > > 
>> > > BUG: unable to handle kernel paging request at 07c06d16
>> > > IP: [<c050c336>] strnlen+0x6/0x20
>> > 
>> > It seems that m->private is of type (void *) while the original v is
>> > (unsigned long *). Can be fixed by the following patch.
>> 
>> Fixed by this patch. Thank you.
>
>Great, thanks!
>
>> By the way, GCC treats "(void *) + offset" as "(char *) + offset"
>> but it is GCC specific extention. Maybe we should avoid such usage
>> in order to avoid build failure for other compilers.
>
>"(void *) + offset" seems to be used quite often.
>
>I tried enable this gcc option, only to see huge amount of warnings.
>
>       -Wpointer-arith
>           Warn about anything that depends on the "size of" a
>           function type or of "void".  GNU C assigns these types a
>           size of 1, for convenience in calculations with "void *"
>           pointers and pointers to functions.
>

Yup! I think it is good to have this.

>/cc/linux-next/scripts/mod/file2alias.c:88: warning: pointer of type ‘void *’ used in arithmetic
...
>/cc/linux-next/scripts/mod/modpost.c:1565: warning: pointer of type ‘void *’ used in arithmetic
>

No problem, this is from kbuild and most of them that I checked are actually fine,
we can send patches to remove these warnings.
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