From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
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, patches@linaro.org,
greearb@candelatech.com, edt@aei.ca,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: [PATCH tip/core/urgent 1/7] rcu: decrease rcu_report_exp_rnp coupling with scheduler
Date: Wed, 20 Jul 2011 11:26:17 -0700 [thread overview]
Message-ID: <1311186383-24819-1-git-send-email-paulmck@linux.vnet.ibm.com> (raw)
In-Reply-To: <20110720182512.GA22946@linux.vnet.ibm.com>
PREEMPT_RCU read-side critical sections blocking an expedited grace
period invoke rcu_report_exp_rnp(). When the last such critical section
has completed, rcu_report_exp_rnp() invokes the scheduler to wake up the
task that invoked synchronize_rcu_expedited() -- needlessly holding the
root rcu_node structure's lock while doing so, thus needlessly providing
a way for RCU and the scheduler to deadlock.
This commit therefore releases the root rcu_node structure's lock before
calling wake_up().
Reported-by: Ed Tomlinson <edt@aei.ca>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
kernel/rcutree_plugin.h | 6 ++++--
1 files changed, 4 insertions(+), 2 deletions(-)
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 75113cb..6abef3c 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -695,9 +695,12 @@ static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp)
raw_spin_lock_irqsave(&rnp->lock, flags);
for (;;) {
- if (!sync_rcu_preempt_exp_done(rnp))
+ if (!sync_rcu_preempt_exp_done(rnp)) {
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
break;
+ }
if (rnp->parent == NULL) {
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
wake_up(&sync_rcu_preempt_exp_wq);
break;
}
@@ -707,7 +710,6 @@ static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp)
raw_spin_lock(&rnp->lock); /* irqs already disabled */
rnp->expmask &= ~mask;
}
- raw_spin_unlock_irqrestore(&rnp->lock, flags);
}
/*
--
1.7.3.2
next prev parent reply other threads:[~2011-07-20 18:28 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-07-20 0:17 [PATCH rcu/urgent 0/6] Fixes for RCU/scheduler/irq-threads trainwreck Paul E. McKenney
2011-07-20 0:18 ` [PATCH tip/core/urgent 1/7] rcu: decrease rcu_report_exp_rnp coupling with scheduler Paul E. McKenney
2011-07-20 2:40 ` Peter Zijlstra
2011-07-20 4:54 ` Paul E. McKenney
2011-07-20 11:23 ` Ed Tomlinson
2011-07-20 11:31 ` Ed Tomlinson
2011-07-20 12:35 ` Peter Zijlstra
2011-07-20 13:23 ` Paul E. McKenney
2011-07-20 0:18 ` [PATCH tip/core/urgent 2/7] rcu: Fix RCU_BOOST race handling current->rcu_read_unlock_special Paul E. McKenney
2011-07-20 0:18 ` [PATCH tip/core/urgent 3/7] rcu: Streamline code produced by __rcu_read_unlock() Paul E. McKenney
2011-07-20 0:18 ` [PATCH tip/core/urgent 4/7] rcu: protect __rcu_read_unlock() against scheduler-using irq handlers Paul E. McKenney
2011-07-20 12:54 ` Peter Zijlstra
2011-07-20 13:25 ` Paul E. McKenney
2011-07-20 0:18 ` [PATCH tip/core/urgent 5/7] sched: Add irq_{enter,exit}() to scheduler_ipi() Paul E. McKenney
2011-07-20 0:18 ` [PATCH tip/core/urgent 6/7] softirq,rcu: Inform RCU of irq_exit() activity Paul E. McKenney
2011-07-20 0:18 ` [PATCH tip/core/urgent 7/7] signal: align __lock_task_sighand() irq disabling and RCU Paul E. McKenney
2011-07-20 1:10 ` [PATCH rcu/urgent 0/6] Fixes for RCU/scheduler/irq-threads trainwreck Ben Greear
2011-07-20 1:30 ` Ed Tomlinson
2011-07-20 2:07 ` Ed Tomlinson
2011-07-20 4:44 ` Paul E. McKenney
2011-07-20 5:03 ` Linus Torvalds
2011-07-20 13:34 ` Paul E. McKenney
2011-07-20 17:02 ` Ben Greear
2011-07-20 17:15 ` Paul E. McKenney
2011-07-20 18:44 ` Ingo Molnar
2011-07-20 18:52 ` Peter Zijlstra
2011-07-20 19:01 ` Paul E. McKenney
2011-07-20 19:25 ` Peter Zijlstra
2011-07-20 20:06 ` Paul E. McKenney
2011-07-20 19:02 ` Linus Torvalds
2011-07-20 19:29 ` Paul E. McKenney
2011-07-20 19:39 ` Ingo Molnar
2011-07-20 19:57 ` Ingo Molnar
2011-07-20 20:33 ` Paul E. McKenney
2011-07-20 20:54 ` Ben Greear
2011-07-20 21:12 ` Paul E. McKenney
2011-07-21 3:25 ` Ben Greear
2011-07-21 16:04 ` Paul E. McKenney
2011-07-20 21:04 ` [GIT PULL] RCU fixes for v3.0 Ingo Molnar
2011-07-20 21:55 ` Ed Tomlinson
2011-07-20 22:06 ` Paul E. McKenney
2011-07-20 20:08 ` [PATCH rcu/urgent 0/6] Fixes for RCU/scheduler/irq-threads trainwreck Paul E. McKenney
2011-07-20 21:05 ` Peter Zijlstra
2011-07-20 21:39 ` Paul E. McKenney
2011-07-20 10:49 ` Ed Tomlinson
2011-07-20 18:25 ` [PATCH rcu/urgent 0/7 v2] " Paul E. McKenney
2011-07-20 18:26 ` Paul E. McKenney [this message]
2011-07-20 18:26 ` [PATCH tip/core/urgent 2/7] rcu: Fix RCU_BOOST race handling current->rcu_read_unlock_special Paul E. McKenney
2011-07-20 18:26 ` [PATCH tip/core/urgent 3/7] rcu: Streamline code produced by __rcu_read_unlock() Paul E. McKenney
2011-07-20 22:44 ` Linus Torvalds
2011-07-21 5:09 ` Paul E. McKenney
2011-07-20 18:26 ` [PATCH tip/core/urgent 4/7] rcu: protect __rcu_read_unlock() against scheduler-using irq handlers Paul E. McKenney
2011-07-20 18:26 ` [PATCH tip/core/urgent 5/7] sched: Add irq_{enter,exit}() to scheduler_ipi() Paul E. McKenney
2011-07-20 18:26 ` [PATCH tip/core/urgent 6/7] softirq,rcu: Inform RCU of irq_exit() activity Paul E. McKenney
2011-07-20 18:26 ` [PATCH tip/core/urgent 7/7] signal: align __lock_task_sighand() irq disabling and RCU Paul E. McKenney
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