linux-kernel - Re: Please add to stable: module: don't unlink the module until we've removed all exposure.

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Date:	Sun, 2 Jun 2013 23:46:33 -0400 (EDT)
From:	Joe Lawrence <joe.lawrence@...atus.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
cc:	Ben Greear <greearb@...delatech.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	stable@...el.org, Joe Lawrence <joe.lawrence@...atus.com>
Subject: Re: Please add to stable:  module: don't unlink the module until
 we've removed all exposure.

On Sun, 2 Jun 2013, Rusty Russell wrote:

> Ben Greear <greearb@...delatech.com> writes:
> 
> > It turns out, the bug I spent yesterday chasing in various 3.9 kernels is apparently
> > fixed by the commit in the title (c9c390bb5535380d40614571894ef0c00bc026ff).
> 
> Apparently being the operative word.
> 
> This commit avoids the entire "module insert failed due to sysfs race"
> path in the common case, it doesn't fix any actual problem.
> 
> I think the real commit you want is Linus' kobject fix
> a49b7e82cab0f9b41f483359be83f44fbb6b4979 "kobject: fix kset_find_obj()
> race with concurrent last kobject_put()".
> 
> Or is that already in stable?

Hi Rusty,

I had pointed Ben (offlist) to that bugzilla entry without realizing
there were other earlier related fixes in this space.  Re-viewing bz-
58011, it looks like it was opened against 3.8.12, while Ben and myself
had encountered module loading problems in versions 3.9 and
3.9.[1-3].  I can update the bugzilla entry to add a comment noting commit
a49b7e82 "kobject: fix kset_find_obj() race with concurrent last
kobject_put()".

That said, it doesn't appear that commit 944a1fa "module: don't unlink the
module until we've removed all exposure" has not made it into any stable  
kernel.  On my system, applying this on top of 3.9 resolved a module
unload/load race that would occasionally occur on boot (two video adapters
of the same make, the module unloads for whatever reason and I see "module
is already loaded" and "sysfs: cannot create duplicate filename
'/module/mgag200'" messages every 5-10% instances.)  I have logs if you
were interested in these warnings/crashes.

Hope this clarifies things.

Regards,

-- Joe
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