linux-kernel - Re: frequent lockups in 3.18rc4

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Message-ID: <20141202191143.GN25340@linux.vnet.ibm.com>
Date:	Tue, 2 Dec 2014 11:11:43 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Dâniel Fraga <fragabr@...il.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: frequent lockups in 3.18rc4

On Tue, Dec 02, 2014 at 04:47:31PM -0200, Dâniel Fraga wrote:
> On Tue, 2 Dec 2014 10:42:02 -0800
> "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> wrote:
> 
> > I was actually suggesting something a bit different.  Instead of bisecting
> > by release, bisect by code.  The procedure is as follows:
> > 
> > 1.	I figure out some reliable way of making RCU allow preemption to
> > 	be disabled for some RCU read-side critical sections, but not for
> > 	others.  I send you the patch, which has rcu_read_lock_test()
> > 	as well as rcu_read_lock().
> > 
> > 2.	You build a kernel without my Kconfig hack, with my patch from
> > 	#1 above, and build a kernel with CONFIG_PREEMPT=y (which of
> > 	course implies CONFIG_TREE_PREEMPT_RCU=y, given that you are
> > 	building without my Kconfig hack).
> > 
> > 3.	You make a list of all the rcu_read_lock() uses in the kernel
> > 	(or ask me to provide it).  You change the rcu_read_lock()
> > 	calls in the first half of this list to rcu_read_lock_test().
> > 
> > 	If the kernel locks up as easily with this change as it did
> > 	in a stock CONFIG_PREEMPT=y CONFIG_TREE_PREEMPT_RCU=y kernel,
> > 	change half of the remaining rcu_read_lock() calls to
> > 	rcu_read_lock_test().  If the kernel is much more resistant
> > 	to lockup, change half of the rcu_read_lock_test() calls
> > 	back to rcu_read_lock().
> 
> 	Ok Paul, I want to do everything I can to help you debug this.
> 
> 	So can you provide me the list you mentioned at point 3 (or
> tell me how can I get it)? If you guide me through this, I can do
> whatever you need. Thanks!

OK.  I need to know exactly what version of the Linux kernel you are
using.  3.18-rc7?  (I am not too worried about exactly which version
you are using as long as I know which version it is.)

							Thanx, Paul

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