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

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Message-ID: <20101104033148.GB5210@cr0.nay.redhat.com>
Date:	Thu, 4 Nov 2010 11:31:48 +0800
From:	Américo Wang <xiyou.wangcong@...il.com>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	Américo Wang <xiyou.wangcong@...il.com>,
	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 10:53:41AM +0800, Wu Fengguang wrote:
>On Thu, Nov 04, 2010 at 10:52:51AM +0800, Américo Wang wrote:
>> 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.
>
>Confirmed. Now my full kernel build is complete and the above are the
>only warnings I see. So it should be easy to add the -Wpointer-arith
>check.
>

Well, after I tried to compile with it, I got lots of warnings.
Most of them that I checked is something like:

 (void *) CONST_PTR + OFFSET

in macros. In order to fix this, we need to:

 (void *) ((char *) CONST_PTR + OFFSET)

So, we have to make some efforts to kill all the warnings. :-/
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