Message-ID: <1332376277.12332.22.camel@lade.trondhjem.org>
Date:	Thu, 22 Mar 2012 00:31:17 +0000
From:	"Myklebust, Trond" <Trond.Myklebust@...app.com>
To:	Boaz Harrosh <bharrosh@...asas.com>
CC:	Greg KH <gregkh@...uxfoundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	"keyrings@...ux-nfs.org" <keyrings@...ux-nfs.org>,
	"linux-security-module@...r.kernel.org" 
	<linux-security-module@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	NFS list <linux-nfs@...r.kernel.org>,
	"Bhamare, Sachin" <sbhamare@...asas.com>,
	David Howells <dhowells@...hat.com>,
	Eric Paris <eparis@...hat.com>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	Kay Sievers <kay.sievers@...y.org>,
	James Morris <jmorris@...ei.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Greg Kroah-Hartman <gregkh@...e.de>
Subject: Re: [PATCHSET 0/4] kmod: Optional timeout on the wait in
 call_usermodehelper_exec

On Wed, 2012-03-21 at 17:18 -0700, Boaz Harrosh wrote:
> On 03/21/2012 08:35 AM, Greg KH wrote:
> > On Tue, Mar 20, 2012 at 04:18:49PM -0700, Boaz Harrosh wrote:
> >> Andrew Hi
> >>
> >> I'm picking on you because I don't have any one else to pick on.
> >> The 3 first patches here, are just good for today. Please see if
> >> you would like to take them? or tell me who should take them?
> >>
> >> The 4th patch is an RFC, which got me looking into this.
> >>
> >> My motivation is that I added yet another Kernel dependency on the
> >> call_usermodehelper() function and am not completely happy with the
> >> error case of having the user-mode program stuck forever. In such
> >> case I would like the Kernel part to timeout and properly error recover
> >> and clean up. So therefor the proposed 4th patch.
> > 
> > What is this new use of call_usermodhelper that you are doing this work
> > for?  Ideally, you never want to make this call, as it's slow and messy,
> > as you have found out.  Is there an in-kernel user that you have
> > recently added?
> > 
> > thanks,
> > 
> > greg k-h
> 
> I agree hence my comment in the 4th patch:
> 	"In the blasphemous occasions that a the Kernel must call a user-mode program"
> 
> I have added a new caller, to the nfs/objectlayoutdriver.ko that uses this
> facility for auto-login into osd-targets (iscsi-targets) when new are requested
> by the filesystem. This auto-login facility is mandated by the pnfs-objects
> standard because in a large cluster filesystems for which pnfs was invented, storage
> devices break and changed everyday, and a manual login by every client is not
> feasible.
> 
> You can see this patch as posted to the mailing list here:
> 	http://article.gmane.org/gmane.linux.nfs/48024/match=login
> 	[title: pnfs-obj: autologin: Add support for protocol autologin]
> 
> It works very well and was heavily tested, with all error scenarios, but
> the theoretical possibility that the user-mode program can be stuck forever
> bothers me and I would like to do something about it. With this patch the
> Kernel can recover cleanly and continue. I have actually tested this part
> and it works as expected.

Hi Boaz,

As an alternative suggestion: since you are always calling the
same /sbin/osd_login userspace program, wouldn't it be easier to add the
timeout smarts into that program? If you can't modify the osd_login
program itself, then it should still be trivial to wrap it with a script
that adds the 'timeout' command prefix.

Cheers
  Trond
-- 
Trond Myklebust
Linux NFS client maintainer

NetApp
Trond.Myklebust@...app.com
www.netapp.com

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