From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Pranith Kumar <bobby.prani@gmail.com>
Cc: Josh Triplett <josh@joshtriplett.org>,
Steven Rostedt <rostedt@goodmis.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Lai Jiangshan <laijs@cn.fujitsu.com>,
"open list:READ-COPY UPDATE..." <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 10/16] rcu: Check for RCU_FLAG_GP_INIT bit in gp_flags for spurious wakeup
Date: Wed, 23 Jul 2014 05:23:35 -0700 [thread overview]
Message-ID: <20140723122335.GK11241@linux.vnet.ibm.com> (raw)
In-Reply-To: <1406092194-13004-11-git-send-email-bobby.prani@gmail.com>
On Wed, Jul 23, 2014 at 01:09:47AM -0400, Pranith Kumar wrote:
> rcu_gp_init() is called once the gp_kthread wakes up on the condition that
> the init bit is set in the gp_flags. For a spurious wakeup we need to check that
> it is actually set. This commit ensures that the RCU_GP_FLAG_INIT bit is set in
> gp_flags.
>
> Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
The trick here is that the other bits have no meaning if we are not yet
in a grace period. If any get spuriously set, for example, by a race
between force_quiescent_state() and the end of a grace period, we really
do want to clear them all.
So sorry, but no.
Thanx, Paul
> ---
> kernel/rcu/tree.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 8d598a2..f8847d9 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -1600,7 +1600,7 @@ static int rcu_gp_init(struct rcu_state *rsp)
> rcu_bind_gp_kthread();
> raw_spin_lock_irq(&rnp->lock);
> smp_mb__after_unlock_lock();
> - if (!ACCESS_ONCE(rsp->gp_flags)) {
> + if (!(ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_INIT)) {
> /* Spurious wakeup, tell caller to go back to sleep. */
> raw_spin_unlock_irq(&rnp->lock);
> return 0;
> --
> 2.0.0.rc2
>
next prev parent reply other threads:[~2014-07-23 12:23 UTC|newest]
Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-07-23 5:09 [PATCH 00/16] rcu: Some minor fixes and cleanups Pranith Kumar
2014-07-23 5:09 ` [PATCH 01/16] rcu: Use rcu_num_nodes instead of NUM_RCU_NODES Pranith Kumar
2014-07-23 5:09 ` [PATCH 02/16] rcu: Check return value for cpumask allocation Pranith Kumar
2014-07-23 12:06 ` Paul E. McKenney
2014-07-23 12:49 ` Pranith Kumar
2014-07-23 17:14 ` Pranith Kumar
2014-07-23 18:01 ` Paul E. McKenney
2014-07-23 5:09 ` [PATCH 03/16] rcu: Fix comment for gp_state field values Pranith Kumar
2014-07-23 5:09 ` [PATCH 04/16] rcu: Remove redundant check for an online CPU Pranith Kumar
2014-07-23 12:09 ` Paul E. McKenney
2014-07-23 13:23 ` Pranith Kumar
2014-07-23 13:41 ` Paul E. McKenney
2014-07-23 14:01 ` Pranith Kumar
2014-07-23 14:14 ` Paul E. McKenney
2014-07-23 15:07 ` Pranith Kumar
2014-07-23 15:21 ` Pranith Kumar
2014-07-23 5:09 ` [PATCH 05/16] rcu: Add noreturn attribute to boost kthread Pranith Kumar
2014-07-23 5:09 ` [PATCH 06/16] rcu: Clear gp_flags only when actually starting new gp Pranith Kumar
2014-07-23 12:13 ` Paul E. McKenney
2014-07-23 5:09 ` [PATCH 07/16] rcu: Save and restore irq flags in rcu_gp_cleanup() Pranith Kumar
2014-07-23 12:16 ` Paul E. McKenney
2014-07-23 5:09 ` [PATCH 08/16] rcu: Clean up rcu_spawn_one_boost_kthread() Pranith Kumar
2014-07-23 5:09 ` [PATCH 09/16] rcu: Remove redundant check for online cpu Pranith Kumar
2014-07-23 12:21 ` Paul E. McKenney
2014-07-23 12:59 ` Pranith Kumar
2014-07-23 13:50 ` Paul E. McKenney
2014-07-23 14:12 ` Pranith Kumar
2014-07-23 14:23 ` Paul E. McKenney
2014-07-23 15:11 ` Pranith Kumar
2014-07-23 15:30 ` Paul E. McKenney
2014-07-23 15:44 ` Pranith Kumar
2014-07-23 19:15 ` Paul E. McKenney
2014-07-23 20:01 ` Pranith Kumar
2014-07-23 20:16 ` Pranith Kumar
2014-07-23 20:23 ` Paul E. McKenney
2014-07-23 5:09 ` [PATCH 10/16] rcu: Check for RCU_FLAG_GP_INIT bit in gp_flags for spurious wakeup Pranith Kumar
2014-07-23 12:23 ` Paul E. McKenney [this message]
2014-07-23 5:09 ` [PATCH 11/16] rcu: Check for spurious wakeup using return value Pranith Kumar
2014-07-23 12:26 ` Paul E. McKenney
2014-07-24 2:36 ` Pranith Kumar
2014-07-24 3:43 ` Paul E. McKenney
2014-07-24 4:03 ` Pranith Kumar
2014-07-24 18:12 ` Paul E. McKenney
2014-07-24 19:59 ` Pranith Kumar
2014-07-24 20:27 ` Paul E. McKenney
2014-07-23 5:09 ` [PATCH 12/16] rcu: Rename rcu_spawn_gp_kthread() to rcu_spawn_kthreads() Pranith Kumar
2014-07-23 5:09 ` [PATCH 13/16] rcu: Spawn nocb kthreads from rcu_prepare_kthreads() Pranith Kumar
2014-07-23 5:09 ` [PATCH 14/16] rcu: Remove redundant checks for rcu_scheduler_fully_active Pranith Kumar
2014-07-23 12:27 ` Paul E. McKenney
2014-07-23 5:09 ` [PATCH 15/16] rcu: Check for a nocb cpu before trying to spawn nocb threads Pranith Kumar
2014-07-23 12:28 ` Paul E. McKenney
2014-07-23 13:14 ` Pranith Kumar
2014-07-23 13:42 ` Paul E. McKenney
2014-07-23 5:09 ` [PATCH 16/16] rcu: kvm.sh: Fix error when you pass --cpus argument Pranith Kumar
2014-07-23 12:31 ` Paul E. McKenney
2014-07-23 14:45 ` [PATCH 00/16] rcu: Some minor fixes and cleanups Paul E. McKenney
2014-08-27 1:10 ` Pranith Kumar
2014-08-27 3:20 ` Paul E. McKenney
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