Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751546AbbFAShl (ORCPT ); Mon, 1 Jun 2015 14:37:41 -0400 Received: from e33.co.us.ibm.com ([32.97.110.151]:39737 "EHLO e33.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753833AbbFASh1 (ORCPT ); Mon, 1 Jun 2015 14:37:27 -0400 Date: Mon, 1 Jun 2015 11:37:21 -0700 From: "Paul E. McKenney" To: Alexander Gordeev Cc: linux-kernel@vger.kernel.org, Steven Rostedt Subject: Re: [PATCH v2 1/9] rcu: Panic if RCU tree can not accommodate all CPUs Message-ID: <20150601183720.GY5989@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1e5e5cf188c90193dc176caa5b6270606ae7af5b.1432889921.git.agordeev@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1e5e5cf188c90193dc176caa5b6270606ae7af5b.1432889921.git.agordeev@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 15060118-0009-0000-0000-00000B52F27A Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2724 Lines: 66 On Fri, May 29, 2015 at 11:53:37AM +0200, Alexander Gordeev wrote: > Currently a condition when RCU tree is unable to accommodate > the configured number of CPUs is not permitted and causes > a fall back to compile-time values. However, the code has no > means to exceed the RCU tree capacity neither at compile-time > nor in run-time. Therefore, if the condition is met in run- > time then it indicates a serios problem elsewhere and should > be handled with a panic. > > Cc: "Paul E. McKenney" > Cc: Steven Rostedt > Signed-off-by: Alexander Gordeev > --- > kernel/rcu/tree.c | 15 +++++++++------ > 1 file changed, 9 insertions(+), 6 deletions(-) > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index 2fce662..66a4230 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -4117,16 +4117,19 @@ static void __init rcu_init_geometry(void) > rcu_capacity[i] = rcu_capacity[i - 1] * RCU_FANOUT; > > /* > + * The tree must be able to accommodate the configured number of CPUs. > + * If this limit is exceeded than we have a serious problem elsewhere. > + * > * The boot-time rcu_fanout_leaf parameter is only permitted > * to increase the leaf-level fanout, not decrease it. Of course, > * the leaf-level fanout cannot exceed the number of bits in > - * the rcu_node masks. Finally, the tree must be able to accommodate > - * the configured number of CPUs. Complain and fall back to the > - * compile-time values if these limits are exceeded. > + * the rcu_node masks. Complain and fall back to the compile- > + * time values if these limits are exceeded. > */ > - if (rcu_fanout_leaf < RCU_FANOUT_LEAF || > - rcu_fanout_leaf > sizeof(unsigned long) * 8 || > - n > rcu_capacity[MAX_RCU_LVLS]) { > + if (n > rcu_capacity[MAX_RCU_LVLS]) > + panic("rcu_init_geometry: rcu_capacity[] is too small"); The way this is set up, if the boot parameter (illegally) sets rcu_fanout_lead smaller than RCU_FANOUT_LEAF, we might panic. It would be far better to first check for rcu_fanout_leaf being out of bounds, and only then have the possibility of panic(). That way, a typo in the rcu_fanout_leaf boot paremeter is ignored, but with a splat. Or am I missing something here? Thanx, Paul > + else if (rcu_fanout_leaf < RCU_FANOUT_LEAF || > + rcu_fanout_leaf > sizeof(unsigned long) * 8) { > WARN_ON(1); > return; > } > -- > 1.8.3.1 > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/