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Date: Mon, 1 Dec 2014 15:08:13 -0800
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: =?iso-8859-1?Q?D=E2niel?= Fraga <fragabr@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: frequent lockups in 3.18rc4
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On Mon, Dec 01, 2014 at 06:28:31PM -0200, Dâniel Fraga wrote:
> On Mon, 1 Dec 2014 11:14:31 -0800
> "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote:
> 
> > If it would help to have !CONFIG_TREE_PREEMPT_RCU with CONFIG_PREEMPT=y,
> > please let me know and I will create a patch that forces this.
> > (Not mainline material, but if it helps with debug...)
> 
> 	Hi Paul. Please, I'd like the patch, because without
> preemption, I'm unable to trigger this bug.

Well, this turned out to be way simpler than I expected.  Passes
light rcutorture testing.  Sometimes you get lucky...

							Thanx, Paul


diff --git a/init/Kconfig b/init/Kconfig
index 903505e66d1d..2cf71fcd514f 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -469,7 +469,7 @@ choice
 
 config TREE_RCU
 	bool "Tree-based hierarchical RCU"
-	depends on !PREEMPT && SMP
+	depends on SMP
 	select IRQ_WORK
 	help
 	  This option selects the RCU implementation that is