Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756089AbZISH7T (ORCPT ); Sat, 19 Sep 2009 03:59:19 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755642AbZISH7R (ORCPT ); Sat, 19 Sep 2009 03:59:17 -0400 Received: from hera.kernel.org ([140.211.167.34]:53846 "EHLO hera.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755211AbZISH7I (ORCPT ); Sat, 19 Sep 2009 03:59:08 -0400 Date: Sat, 19 Sep 2009 07:58:51 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: <12532926201851-git-send-email-> References: <12532926201851-git-send-email-> To: linux-tip-commits@vger.kernel.org Subject: [tip:core/urgent] rcu: Apply results of code inspection of kernel/rcutree_plugin.h Message-ID: Git-Commit-ID: e7d8842ed34a7fe19d1ed90f84c211fb056ac523 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]); Sat, 19 Sep 2009 07:58:52 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5811 Lines: 150 Commit-ID: e7d8842ed34a7fe19d1ed90f84c211fb056ac523 Gitweb: http://git.kernel.org/tip/e7d8842ed34a7fe19d1ed90f84c211fb056ac523 Author: Paul E. McKenney AuthorDate: Fri, 18 Sep 2009 09:50:18 -0700 Committer: Ingo Molnar CommitDate: Sat, 19 Sep 2009 08:53:21 +0200 rcu: Apply results of code inspection of kernel/rcutree_plugin.h o Drop the calls to cpu_quiet() from the online/offline code. These are unnecessary, since force_quiescent_state() will clean up, and removing them simplifies the code a bit. o Add a warning to check that we don't enqueue the same blocked task twice onto the ->blocked_tasks[] lists. o Rework the phase computation in rcu_preempt_note_context_switch() to be more readable, as suggested by Josh Triplett. o Disable irqs to close a race between the scheduling clock interrupt and rcu_preempt_note_context_switch() WRT the ->rcu_read_unlock_special field. o Add comments to rnp->lock acquisition and release within rcu_read_unlock_special() noting that irqs are already disabled. 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: <12532926201851-git-send-email-> Signed-off-by: Ingo Molnar --- kernel/rcutree.c | 27 +++++---------------------- kernel/rcutree_plugin.h | 10 ++++++---- 2 files changed, 11 insertions(+), 26 deletions(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index e8624eb..ae4a553 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -767,10 +767,10 @@ cpu_quiet_msk(unsigned long mask, struct rcu_state *rsp, struct rcu_node *rnp, /* * Record a quiescent state for the specified CPU, which must either be - * the current CPU or an offline CPU. The lastcomp argument is used to - * make sure we are still in the grace period of interest. We don't want - * to end the current grace period based on quiescent states detected in - * an earlier grace period! + * the current CPU. The lastcomp argument is used to make sure we are + * still in the grace period of interest. We don't want to end the current + * grace period based on quiescent states detected in an earlier grace + * period! */ static void cpu_quiet(int cpu, struct rcu_state *rsp, struct rcu_data *rdp, long lastcomp) @@ -805,7 +805,6 @@ cpu_quiet(int cpu, struct rcu_state *rsp, struct rcu_data *rdp, long lastcomp) * This GP can't end until cpu checks in, so all of our * callbacks can be processed during the next GP. */ - rdp = rsp->rda[smp_processor_id()]; rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL]; cpu_quiet_msk(mask, rsp, rnp, flags); /* releases rnp->lock */ @@ -881,9 +880,6 @@ static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp) spin_unlock(&rsp->onofflock); /* irqs remain disabled. */ - /* Being offline is a quiescent state, so go record it. */ - cpu_quiet(cpu, rsp, rdp, lastcomp); - /* * Move callbacks from the outgoing CPU to the running CPU. * Note that the outgoing CPU is now quiscent, so it is now @@ -1448,20 +1444,7 @@ rcu_init_percpu_data(int cpu, struct rcu_state *rsp, int preemptable) rnp = rnp->parent; } while (rnp != NULL && !(rnp->qsmaskinit & mask)); - spin_unlock(&rsp->onofflock); /* irqs remain disabled. */ - - /* - * A new grace period might start here. If so, we will be part of - * it, and its gpnum will be greater than ours, so we will - * participate. It is also possible for the gpnum to have been - * incremented before this function was called, and the bitmasks - * to not be filled out until now, in which case we will also - * participate due to our gpnum being behind. - */ - - /* Since it is coming online, the CPU is in a quiescent state. */ - cpu_quiet(cpu, rsp, rdp, lastcomp); - local_irq_restore(flags); + spin_unlock_irqrestore(&rsp->onofflock, flags); } static void __cpuinit rcu_online_cpu(int cpu) diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 5f94619..cd6047c 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -117,9 +117,9 @@ static void rcu_preempt_note_context_switch(int cpu) * on line! */ WARN_ON_ONCE((rdp->grpmask & rnp->qsmaskinit) == 0); - phase = !(rnp->qsmask & rdp->grpmask) ^ (rnp->gpnum & 0x1); + WARN_ON_ONCE(!list_empty(&t->rcu_node_entry)); + phase = (rnp->gpnum + !(rnp->qsmask & rdp->grpmask)) & 0x1; list_add(&t->rcu_node_entry, &rnp->blocked_tasks[phase]); - smp_mb(); /* Ensure later ctxt swtch seen after above. */ spin_unlock_irqrestore(&rnp->lock, flags); } @@ -133,7 +133,9 @@ static void rcu_preempt_note_context_switch(int cpu) * means that we continue to block the current grace period. */ rcu_preempt_qs(cpu); + local_irq_save(flags); t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS; + local_irq_restore(flags); } /* @@ -189,10 +191,10 @@ static void rcu_read_unlock_special(struct task_struct *t) */ for (;;) { rnp = t->rcu_blocked_node; - spin_lock(&rnp->lock); + spin_lock(&rnp->lock); /* irqs already disabled. */ if (rnp == t->rcu_blocked_node) break; - spin_unlock(&rnp->lock); + spin_unlock(&rnp->lock); /* irqs remain disabled. */ } empty = list_empty(&rnp->blocked_tasks[rnp->gpnum & 0x1]); list_del_init(&t->rcu_node_entry); -- 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/