linux-kernel - Re: PROBLEM: 3.0-rc kernels unbootable since -rc3

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Date:	Thu, 7 Jul 2011 12:58:45 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	julie Sullivan <kernelmail.jms@...il.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, josh@...htriplett.org,
	niv@...ibm.com, tglx@...utronix.de, peterz@...radead.org,
	rostedt@...dmis.org, Valdis.Kletnieks@...edu, dhowells@...hat.com,
	eric.dumazet@...il.com, darren@...art.com, patches@...aro.org,
	torvalds@...ux-foundation.org
Subject: Re: PROBLEM: 3.0-rc kernels unbootable since -rc3

On Thu, Jul 07, 2011 at 08:47:13PM +0100, julie Sullivan wrote:
> On Wednesday 06 July 2011 22:23:48 Paul E. McKenney wrote:
> > On Wed, Jul 06, 2011 at 10:10:16PM +0100, julie Sullivan wrote:
> > > None of my kernels after 3.0-rc3 will boot on my Dell XPS-M1730
> > > (x86-64 2-core) test box running
> > > Ubuntu (Kubuntu) 11.04 (i.e. the first unbootable one was -rc4).
> > > The machine freezes immediately after selecting the kernel from the
> > > bootloader menu, leaving
> > > me with a blank blue screen so I can't give you any log messages.
> > > 
> > > It bisects to the following commit:
> > > 
> > > commit a46e0899eec7a3069bcadd45dfba7bf67c6ed016
> > > Author: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > > Date:   Wed Jun 15 15:47:09 2011 -0700
> > > 
> > >     rcu: use softirq instead of kthreads except when RCU_BOOST=y
> > >     
> > >     This patch #ifdefs RCU kthreads out of the kernel unless RCU_BOOST=y,
> > >     thus eliminating context-switch overhead if RCU priority boosting has
> > >     not been configured.
> > >     
> > >     Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> 
> > 
> > Hello, Julie,
> > 
> > One approach would be to cherry-pick the following commits:
> >
> > f8b7fc6b514f34a51875dd48dff70d4d17a54f38 rcu: Move RCU_BOOST #ifdefs to header f
> > a46e0899eec7a3069bcadd45dfba7bf67c6ed016 rcu: use softirq instead of kthreads ex
> > 09223371deac67d08ca0b70bd18787920284c967 rcu: Use softirq to address performance
> > 9a432736904d386cda28b987b38ba14dae960ecc rcu: Simplify curing of load woes
> 
> > 
> > Another approach would be to move ahead to v3.0-rc4 or later.
> > 
> > 							Thanx, Paul
> 
> Hi Paul
> Thanks for your prompt reply, sorry for the delay in mine (real life intervened :-)
> I tried reverting those 4 commits on v3.0-rc4 and can confirm that it _does_ give me a bootable 3.0-rc4 kernel.
> I'll do some more testing. If you would like me to try anything specific just let me know :-)

What happens if you revert only these two?

f8b7fc6b514f34a51875dd48dff70d4d17a54f38 rcu: Move RCU_BOOST #ifdefs to header f
a46e0899eec7a3069bcadd45dfba7bf67c6ed016 rcu: use softirq instead of kthreads ex

If that works, perhaps we should try to break down a46e0899ee into
smaller pieces to see what is causing the trouble.

								Thanx, Paul
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