linux-kernel - Re: Reading /proc/kcore causes a BUG()

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Message-Id: <20090904103156.a04179f3.akpm@linux-foundation.org>
Date:	Fri, 4 Sep 2009 10:31:56 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Nick Craig-Wood <nick@...ig-wood.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: Reading /proc/kcore causes a BUG()

On Fri, 4 Sep 2009 18:16:45 +0900 KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:

> On Fri, 4 Sep 2009 10:00:39 +0100
> Nick Craig-Wood <nick@...ig-wood.com> wrote:
> 
> > On Fri, Sep 04, 2009 at 09:06:42AM +0900, KAMEZAWA Hiroyuki wrote:
> > > On Thu, 3 Sep 2009 15:14:55 +0300
> > > Pekka Enberg <penberg@...helsinki.fi> wrote:
> > > > On Thu, Sep 3, 2009 at 2:34 PM, Nick Craig-Wood<nick@...ig-wood.com> wrote:
> > > > > Is a fix for this going to make 2.6.31?
> > > > >
> > > > > To replicate
> > > > >
> > > > > __cat /proc/kcore >/dev/null
> > > > >
> > > > > See also
> > > > >
> > > > > __http://bugzilla.kernel.org/show_bug.cgi?id=13850
> > [snip]
> > > > > I tried this on the latest git checkout (as of 2009-09-03 11:00 GMT)
> > > > > under Xen as a domU. __The bugzilla report states it happens on non xen
> > > > > machines also.

Is this a regression?  I've lost track..

> > > > > I know reading /proc/kcore isn't such a good idea, but badly written
> > > > > backup scripts are triggering this on our customer's servers :-(
> > > > 
> > > > AFAICT the bug was fixed but I can't seem to find the patches in
> > > > Linus' git either. Lets CC Andrew and Hiroyuki-san.
> > > 
> > > Ah, it's now tested under mmotm. please wait.
> > 
> > I tried mmotm but I couldn't get it to boot under Xen :-(
> > 
> > If you send me a patch against latest git I'm willing to test it (I
> > tried to extract the relevant patch from mmotm but failed dismally)
> > 
> > Thanks
> > 
> 
> If you already downloaded mmotm, use these patches.
> 
> vmalloc-unmap-vmalloc-area-after-hiding-it.patch
> kcore-fix-vread-vwrite-to-be-aware-of-holes.patch
> kcore-fix-vread-vwrite-to-be-aware-of-holes-update.patch
> kcore-proc-kcore-should-use-vread.patch
> 
> All I tested was x86-32/x86-64. then more tests are welcomed.

That's a lot of stuff for 2.6.31.  Is there some simple quickfix we can do?
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