Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755891Ab1BWBkB (ORCPT ); Tue, 22 Feb 2011 20:40:01 -0500 Received: from e39.co.us.ibm.com ([32.97.110.160]:35130 "EHLO e39.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755856Ab1BWBkA (ORCPT ); Tue, 22 Feb 2011 20:40:00 -0500 From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: mingo@elte.hu, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca, josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com, eric.dumazet@gmail.com, darren@dvhart.com, "Paul E. McKenney" Subject: [PATCH RFC tip/core/rcu 05/11] rcu: add comment saying why DEBUG_OBJECTS_RCU_HEAD depends on PREEMPT. Date: Tue, 22 Feb 2011 17:39:34 -0800 Message-Id: <1298425183-21265-5-git-send-email-paulmck@linux.vnet.ibm.com> X-Mailer: git-send-email 1.7.3.2 In-Reply-To: <20110223013917.GA20996@linux.vnet.ibm.com> References: <20110223013917.GA20996@linux.vnet.ibm.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1351 Lines: 33 The build will break if you change the Kconfig to allow DEBUG_OBJECTS_RCU_HEAD and !PREEMPT, so document the reasoning near where the breakage would occur. Signed-off-by: Paul E. McKenney --- kernel/rcupdate.c | 5 +++++ 1 files changed, 5 insertions(+), 0 deletions(-) diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c index afd21d1..f3240e9 100644 --- a/kernel/rcupdate.c +++ b/kernel/rcupdate.c @@ -214,6 +214,11 @@ static int rcuhead_fixup_free(void *addr, enum debug_obj_state state) * Ensure that queued callbacks are all executed. * If we detect that we are nested in a RCU read-side critical * section, we should simply fail, otherwise we would deadlock. + * Note that the machinery to reliably determine whether + * or not we are in an RCU read-side critical section + * exists only in the preemptible RCU implementations + * (TINY_PREEMPT_RCU and TREE_PREEMPT_RCU), which is why + * DEBUG_OBJECTS_RCU_HEAD is disallowed if !PREEMPT. */ if (rcu_preempt_depth() != 0 || preempt_count() != 0 || irqs_disabled()) { -- 1.7.3.2 -- 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/