Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758173AbZIOHS2 (ORCPT ); Tue, 15 Sep 2009 03:18:28 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758165AbZIOHSV (ORCPT ); Tue, 15 Sep 2009 03:18:21 -0400 Received: from hera.kernel.org ([140.211.167.34]:49502 "EHLO hera.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758156AbZIOHSN (ORCPT ); Tue, 15 Sep 2009 03:18:13 -0400 Date: Tue, 15 Sep 2009 07:17:44 GMT From: "tip-bot for Paul E. McKenney" Cc: linux-kernel@vger.kernel.org, paulmck@linux.vnet.ibm.com, hpa@zytor.com, mingo@redhat.com, tglx@linutronix.de, mingo@elte.hu Reply-To: mingo@redhat.com, hpa@zytor.com, paulmck@linux.vnet.ibm.com, linux-kernel@vger.kernel.org, tglx@linutronix.de, mingo@elte.hu In-Reply-To: <12528585111986-git-send-email-> References: <12528585111986-git-send-email-> To: linux-tip-commits@vger.kernel.org Subject: [tip:core/urgent] rcu: Add debug checks to TREE_PREEMPT_RCU for premature grace periods Message-ID: Git-Commit-ID: 429e6f07df20175fa59927df415c41c5e1d82d91 X-Mailer: tip-git-log-daemon MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.0 (hera.kernel.org [127.0.0.1]); Tue, 15 Sep 2009 07:17:44 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4470 Lines: 117 Commit-ID: 429e6f07df20175fa59927df415c41c5e1d82d91 Gitweb: http://git.kernel.org/tip/429e6f07df20175fa59927df415c41c5e1d82d91 Author: Paul E. McKenney AuthorDate: Sun, 13 Sep 2009 09:15:09 -0700 Committer: Ingo Molnar CommitDate: Tue, 15 Sep 2009 08:43:58 +0200 rcu: Add debug checks to TREE_PREEMPT_RCU for premature grace periods Check to make sure that there are no blocked tasks for the previous grace period while initializing for the next grace period, verify that rcu_preempt_qs() is given the correct CPU number and is never called for an offline CPU. Signed-off-by: Paul E. McKenney Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: akpm@linux-foundation.org Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu LKML-Reference: <12528585111986-git-send-email-> Signed-off-by: Ingo Molnar --- kernel/rcutree.c | 2 ++ kernel/rcutree_plugin.h | 25 +++++++++++++++++++++++++ 2 files changed, 27 insertions(+), 0 deletions(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index da301e2..e9a4ae9 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -632,6 +632,7 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags) /* Special-case the common single-level case. */ if (NUM_RCU_NODES == 1) { rnp->qsmask = rnp->qsmaskinit; + rcu_preempt_check_blocked_tasks(rnp); rnp->gpnum = rsp->gpnum; rsp->signaled = RCU_SIGNAL_INIT; /* force_quiescent_state OK. */ spin_unlock_irqrestore(&rnp->lock, flags); @@ -665,6 +666,7 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags) for (rnp_cur = &rsp->node[0]; rnp_cur < rnp_end; rnp_cur++) { spin_lock(&rnp_cur->lock); /* irqs already disabled. */ rnp_cur->qsmask = rnp_cur->qsmaskinit; + rcu_preempt_check_blocked_tasks(rnp); rnp->gpnum = rsp->gpnum; spin_unlock(&rnp_cur->lock); /* irqs already disabled. */ } diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 4778936..b8e4b03 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -86,6 +86,7 @@ static void rcu_preempt_qs(int cpu) if (t->rcu_read_lock_nesting && (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) { + WARN_ON_ONCE(cpu != smp_processor_id()); /* Possibly blocking in an RCU read-side critical section. */ rdp = rcu_preempt_state.rda[cpu]; @@ -103,7 +104,11 @@ static void rcu_preempt_qs(int cpu) * state for the current grace period), then as long * as that task remains queued, the current grace period * cannot end. + * + * But first, note that the current CPU must still be + * on line! */ + WARN_ON_ONCE((rdp->grpmask & rnp->qsmaskinit) == 0); phase = !(rnp->qsmask & rdp->grpmask) ^ (rnp->gpnum & 0x1); list_add(&t->rcu_node_entry, &rnp->blocked_tasks[phase]); smp_mb(); /* Ensure later ctxt swtch seen after above. */ @@ -259,6 +264,18 @@ static void rcu_print_task_stall(struct rcu_node *rnp) #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */ /* + * Check that the list of blocked tasks for the newly completed grace + * period is in fact empty. It is a serious bug to complete a grace + * period that still has RCU readers blocked! This function must be + * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock + * must be held by the caller. + */ +static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) +{ + WARN_ON_ONCE(!list_empty(&rnp->blocked_tasks[rnp->gpnum & 0x1])); +} + +/* * Check for preempted RCU readers for the specified rcu_node structure. * If the caller needs a reliable answer, it must hold the rcu_node's * >lock. @@ -451,6 +468,14 @@ static void rcu_print_task_stall(struct rcu_node *rnp) #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */ /* + * Because there is no preemptable RCU, there can be no readers blocked, + * so there is no need to check for blocked tasks. + */ +static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) +{ +} + +/* * Because preemptable RCU does not exist, there are never any preempted * RCU readers. */ -- 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/