Subject: Re: Error returns not handled correctly
	by	sysfs.c:subsys_attr_store()
From: Andrew Patterson <andrew.patterson@hp.com>
To: Tejun Heo <teheo@suse.de>
Cc: Greg KH <greg@kroah.com>, Andrew Morton <akpm@linux-foundation.org>,
       linux-kernel@vger.kernel.org, linux-hotplug@vger.kernel.org
In-Reply-To: <474D1BD4.2050805@suse.de>
References: <1195683419.16019.225.camel@grinch>
	 <20071126203116.0c93cdb9.akpm@linux-foundation.org>
	 <20071127053321.GA975@kroah.com>  <474D1BD4.2050805@suse.de>
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Date: Wed, 28 Nov 2007 12:31:40 -0700
Message-Id: <1196278300.5431.9.camel@grinch>
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On Wed, 2007-11-28 at 16:42 +0900, Tejun Heo wrote:
> Greg KH wrote:
> > On Mon, Nov 26, 2007 at 08:31:16PM -0800, Andrew Morton wrote:
> >> On Wed, 21 Nov 2007 15:16:59 -0700 Andrew Patterson <andrew.patterson@hp.com> wrote:
> >>
> >>> The buf in fs/sysfs.c:subsys_attr_store() does not seem to be updated
> >>> correctly when returning a negative value (indicating that an error
> >>> condition has occurred) is returned.  If a negative value is returned,
> >>> the next subsequent call to subsys_attr_store will have the contents of
> >>> buf appended to the previous call.
> >> subsys_attr_store() gets deleted by
> >> http://www.kernel.org/pub/linux/kernel/people/gregkh/gregkh-2.6/gregkh-01-driver/kset-kill-subsys-attr.patch
> >>
> >> So maybe we will soon accidentally fix whatever-this-is?  Or maybe we will
> >> faithfully maintain it.
> > 
> > Yes, subsys attributes go away, but this is showing a bug in the sysfs
> > core with attributes, not in the "middle" layers of attributes.
> > 
> > I bounced the original bug report to Tejun, who has been changing the
> > logic around this area to see if he sees anything that might be
> > different now.
> > 
> > Tejun?
> 
> Weird, the problem is not reproducible here.
> 
> # echo a > allow_restart
> -bash: echo: write error: Invalid argument
> [  437.518024] buf_ptr = 0xffff810005e20000, buf = x
> [  437.518027] , count = 2
> # echo b > allow_restart
> -bash: echo: write error: Invalid argument
> [  438.972973] buf_ptr = 0xffff81001be6f000, buf = y
> [  438.972976] , count = 2
> # echo c > allow_restart
> -bash: echo: write error: Invalid argument
> [  440.539747] buf_ptr = 0xffff81001d4ba000, buf = z
> [  440.539750] , count = 2
> 
> Which is expected.  On each open, sysfs_buffer is allocated with kzalloc
> and the buffer is freed on close, so I don't see how it can happen.
> Behavior for multiple write can be considered peculiar in that ppos is
> essentially ignored and each write is passed just like brand new write
> to ->store method but this too is the expected behavior.
> 
> # (echo a; echo b; echo c) > allow_restart
> [  765.257132] buf_ptr = 0xffff81001be4f000, buf = a
> [  765.257135] , count = 2
> [  765.285474] buf_ptr = 0xffff81001be4f000, buf = b
> [  765.285484] , count = 2
> [  765.314002] buf_ptr = 0xffff81001be4f000, buf = c
> [  765.314004] , count = 2
> -bash: echo: write error: Invalid argument
> -bash: echo: write error: Invalid argument
> -bash: echo: write error: Invalid argument
> 
> Andrew Petterson, can you please build 2.6.24-rc3 from clean source tree
> and retry?
> 

I tried with clean 2.6.24-rc3 and get the same bad behavior.  This is on
an ia64 box, so maybe that is an issue. I can try on an x86 box as well.
Oh, one other thing.  I tried a "uname -r" to make sure I had the
correct kernel booted and got:

# uname -r
2.6.24-rc3
x
y
z
#

Andrew
-- 
Andrew Patterson
Hewlett-Packard

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