netdev - Re: Top 10 kernel oopses for the week ending January 5th, 2008

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Message-ID: <18314.48266.220382.180206@notabene.brown>
Date:	Mon, 14 Jan 2008 12:36:10 +1100
From:	Neil Brown <neilb@...e.de>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Kevin Winchester <kjwinchester@...il.com>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	NetDev <netdev@...r.kernel.org>, gregkh@...e.de
Subject: Re: Top 10 kernel oopses for the week ending January 5th, 2008

On Thursday January 10, viro@...IV.linux.org.uk wrote:
> On Thu, Jan 10, 2008 at 03:13:48PM +1100, Neil Brown wrote:
> > > What guarantees that it doesn't happen before we get to callback?  AFAICS,
> > > nothing whatsoever...
> > 
> > Yes, that's bad isn't it :-)
> > 
> > I think I should be using sysfs_schedule_callback here.  That makes the 
> > required 'get' and 'put' calls.... but it can fail with -ENOMEM.  I
> > wonder what I do if -ENOMEM???  Maybe I'll just continue to roll my
> > one :-( 
> 
> How about this instead (completely untested)
> 
> 	* split failure exits
> 	* switch to kick_rdev_from_array()
> 	* fold unbind_rdev_from_array() into it (no other callers anymore)
> 	* take export_rdev() into failure case in bind_rdev_to_array()
> 	* in kick_rdev_from_array() do what export_rdev() does sans
> kobject_put() and do that before schedule_work().  Take kobject_put() into
> delayed_delete().

While there are probably some good ideas in there, I think fixing this
particular bug is much simpler.  Just take a reference to the object
before scheduling the worker, and drop it when the worker has done
its work.

I have a closer look at the idea of no required export_rdev after a
failed bind_rdev_to_array.  On the surface it does seem to make the
code nicer.

Thanks,
NeilBrown
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