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

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Date:	Thu, 4 Nov 2010 11:43:49 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Américo Wang <xiyou.wangcong@...il.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 11:31:48AM +0800, Américo Wang wrote:
> 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. :-/

Sorry I didn't run allyesconfig/allmodconfig as suggested by Tetsuo.
So expect more warnings..

Thanks,
Fengguang
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