From: Josh Triplett <josh@joshtriplett.org>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: linux-kernel@vger.kernel.org, mingo@elte.hu,
laijs@cn.fujitsu.com, dipankar@in.ibm.com,
akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca,
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,
fweisbec@gmail.com, sbw@mit.edu, patches@linaro.org,
"Paul E. McKenney" <paul.mckenney@linaro.org>
Subject: Re: [PATCH tip/core/rcu 06/15] rcu: Make offline-CPU checking allow for indefinite delays
Date: Fri, 31 Aug 2012 11:12:37 -0700 [thread overview]
Message-ID: <20120831181237.GD4259@jtriplet-mobl1> (raw)
In-Reply-To: <1346352988-32444-6-git-send-email-paulmck@linux.vnet.ibm.com>
On Thu, Aug 30, 2012 at 11:56:19AM -0700, Paul E. McKenney wrote:
> From: "Paul E. McKenney" <paul.mckenney@linaro.org>
>
> The rcu_implicit_offline_qs() function implicitly assumed that execution
> would progress predictably when interrupts are disabled, which is of course
> not guaranteed when running on a hypervisor. Furthermore, this function
> is short, and is called from one place only in a short function.
>
> This commit therefore ensures that the timing is checked before
> checking the condition, which guarantees correct behavior even given
> indefinite delays. It also inlines rcu_implicit_offline_qs() into
> rcu_implicit_dynticks_qs().
>
> Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
> ---
> kernel/rcutree.c | 53 +++++++++++++++++++++--------------------------------
> 1 files changed, 21 insertions(+), 32 deletions(-)
>
> diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> index 96b8aff..9f44749 100644
> --- a/kernel/rcutree.c
> +++ b/kernel/rcutree.c
> @@ -317,35 +317,6 @@ static struct rcu_node *rcu_get_root(struct rcu_state *rsp)
> }
>
> /*
> - * If the specified CPU is offline, tell the caller that it is in
> - * a quiescent state. Otherwise, whack it with a reschedule IPI.
> - * Grace periods can end up waiting on an offline CPU when that
> - * CPU is in the process of coming online -- it will be added to the
> - * rcu_node bitmasks before it actually makes it online. The same thing
> - * can happen while a CPU is in the process of coming online. Because this
> - * race is quite rare, we check for it after detecting that the grace
> - * period has been delayed rather than checking each and every CPU
> - * each and every time we start a new grace period.
> - */
> -static int rcu_implicit_offline_qs(struct rcu_data *rdp)
> -{
> - /*
> - * If the CPU is offline for more than a jiffy, it is in a quiescent
> - * state. We can trust its state not to change because interrupts
> - * are disabled. The reason for the jiffy's worth of slack is to
> - * handle CPUs initializing on the way up and finding their way
> - * to the idle loop on the way down.
> - */
> - if (cpu_is_offline(rdp->cpu) &&
> - ULONG_CMP_LT(rdp->rsp->gp_start + 2, jiffies)) {
> - trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, "ofl");
> - rdp->offline_fqs++;
> - return 1;
> - }
> - return 0;
> -}
> -
> -/*
> * rcu_idle_enter_common - inform RCU that current CPU is moving towards idle
> *
> * If the new value of the ->dynticks_nesting counter now is zero,
> @@ -675,7 +646,7 @@ static int dyntick_save_progress_counter(struct rcu_data *rdp)
> * Return true if the specified CPU has passed through a quiescent
> * state by virtue of being in or having passed through an dynticks
> * idle state since the last call to dyntick_save_progress_counter()
> - * for this same CPU.
> + * for this same CPU, or by virtue of having been offline.
> */
> static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
> {
> @@ -699,8 +670,26 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
> return 1;
> }
>
> - /* Go check for the CPU being offline. */
> - return rcu_implicit_offline_qs(rdp);
> + /*
> + * Check for the CPU being offline, but only if the grace period
> + * is old enough. We don't need to worry about the CPU changing
> + * state: If we see it offline even once, it has been through a
> + * quiescent state.
> + *
> + * The reason for insisting that the grace period be at least
> + * one jiffy old is that CPUs that are not quite online and that
> + * have just gone offline can still execute RCU read-side critical
> + * sections.
> + */
> + if (ULONG_CMP_GE(rdp->rsp->gp_start + 2, jiffies))
> + return 0; /* Grace period is not old enough. */
> + barrier();
> + if (cpu_is_offline(rdp->cpu)) {
> + trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, "ofl");
> + rdp->offline_fqs++;
> + return 1;
> + }
> + return 0;
> }
>
> static int jiffies_till_stall_check(void)
> --
> 1.7.8
>
next prev parent reply other threads:[~2012-08-31 18:12 UTC|newest]
Thread overview: 86+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-08-30 18:56 [PATCH tip/core/rcu 0/15] Miscellaneous fixes Paul E. McKenney
2012-08-30 18:56 ` [PATCH tip/core/rcu 01/15] rcu: Add PROVE_RCU_DELAY to provoke difficult races Paul E. McKenney
2012-08-30 18:56 ` [PATCH tip/core/rcu 02/15] rcu: Pull TINY_RCU dyntick-idle tracing into non-idle region Paul E. McKenney
2012-08-31 16:53 ` Josh Triplett
2012-08-30 18:56 ` [PATCH tip/core/rcu 03/15] rcu: Properly initialize ->boost_tasks on CPU offline Paul E. McKenney
2012-08-31 17:56 ` Josh Triplett
2012-09-06 14:40 ` Peter Zijlstra
2012-09-06 20:58 ` Paul E. McKenney
2012-08-30 18:56 ` [PATCH tip/core/rcu 04/15] rcu: Permit RCU_NONIDLE() to be used from interrupt context Paul E. McKenney
2012-08-31 18:00 ` Josh Triplett
2012-09-04 22:33 ` Paul E. McKenney
2012-09-04 22:48 ` Josh Triplett
2012-09-04 22:51 ` Steven Rostedt
2012-09-04 23:08 ` Josh Triplett
2012-09-04 23:23 ` Steven Rostedt
2012-09-04 23:33 ` Josh Triplett
2012-09-04 23:43 ` Paul E. McKenney
2012-09-06 18:54 ` Josh Triplett
2012-09-06 19:54 ` Steven Rostedt
2012-09-07 6:09 ` Josh Triplett
2012-09-07 14:24 ` Paul E. McKenney
2012-09-07 14:47 ` Josh Triplett
2012-09-07 15:16 ` Steven Rostedt
2012-09-12 1:07 ` Paul E. McKenney
2012-09-12 14:13 ` Steven Rostedt
2012-09-12 15:03 ` Paul E. McKenney
2012-09-12 15:18 ` Steven Rostedt
2012-09-12 16:57 ` Paul E. McKenney
2012-09-04 23:46 ` Steven Rostedt
2012-09-05 0:42 ` Josh Triplett
2012-09-05 6:23 ` [PATCH] trace: Don't declare trace_*_rcuidle functions in modules Josh Triplett
2012-09-05 14:26 ` Mathieu Desnoyers
2012-09-05 16:36 ` Paul E. McKenney
2012-09-06 19:49 ` Steven Rostedt
2012-09-14 6:07 ` [tip:core/rcu] trace: Don' t " tip-bot for Josh Triplett
2012-09-04 23:14 ` [PATCH tip/core/rcu 04/15] rcu: Permit RCU_NONIDLE() to be used from interrupt context Paul E. McKenney
2012-08-30 18:56 ` [PATCH tip/core/rcu 05/15] rcu: Improve boost selection when moving tasks to root rcu_node Paul E. McKenney
2012-08-31 18:09 ` Josh Triplett
2012-08-30 18:56 ` [PATCH tip/core/rcu 06/15] rcu: Make offline-CPU checking allow for indefinite delays Paul E. McKenney
2012-08-31 18:12 ` Josh Triplett [this message]
2012-08-30 18:56 ` [PATCH tip/core/rcu 07/15] rcu: Fix obsolete rcu_initiate_boost() header comment Paul E. McKenney
2012-08-31 18:13 ` Josh Triplett
2012-08-30 18:56 ` [PATCH tip/core/rcu 08/15] rcu: Apply for_each_rcu_flavor() to increment_cpu_stall_ticks() Paul E. McKenney
2012-08-31 18:15 ` Josh Triplett
2012-09-04 22:44 ` Paul E. McKenney
2012-08-30 18:56 ` [PATCH tip/core/rcu 09/15] rcu: Avoid rcu_print_detail_task_stall_rnp() segfault Paul E. McKenney
2012-08-31 18:19 ` Josh Triplett
2012-09-04 22:46 ` Paul E. McKenney
2012-09-04 22:55 ` Josh Triplett
2012-08-30 18:56 ` [PATCH tip/core/rcu 10/15] rcu: Protect rcu_node accesses during CPU stall warnings Paul E. McKenney
2012-08-31 18:23 ` Josh Triplett
2012-09-04 22:51 ` Paul E. McKenney
2012-09-06 14:51 ` Peter Zijlstra
2012-09-06 21:01 ` Paul E. McKenney
2012-08-30 18:56 ` [PATCH tip/core/rcu 11/15] rcu: Avoid spurious RCU " Paul E. McKenney
2012-08-31 18:24 ` Josh Triplett
2012-09-06 14:56 ` Peter Zijlstra
2012-09-06 15:07 ` Steven Rostedt
2012-09-06 15:19 ` Peter Zijlstra
2012-09-06 21:03 ` Paul E. McKenney
2012-09-06 21:41 ` Steven Rostedt
2012-09-06 21:58 ` Paul E. McKenney
2012-09-06 22:05 ` Steven Rostedt
2012-09-06 22:22 ` Paul E. McKenney
2012-09-07 7:00 ` Peter Zijlstra
2012-09-07 14:42 ` Steven Rostedt
2012-08-30 18:56 ` [PATCH tip/core/rcu 12/15] rcu: Remove redundant memory barrier from __call_rcu() Paul E. McKenney
2012-08-31 18:30 ` Josh Triplett
2012-08-31 18:40 ` Josh Triplett
2012-08-30 18:56 ` [PATCH tip/core/rcu 13/15] rcu: Move TINY_PREEMPT_RCU away from raw_local_irq_save() Paul E. McKenney
2012-08-31 18:34 ` Josh Triplett
2012-09-04 23:03 ` Paul E. McKenney
2012-08-30 18:56 ` [PATCH tip/core/rcu 14/15] time: RCU permitted to stop idle entry via softirq Paul E. McKenney
2012-08-31 18:51 ` Josh Triplett
2012-09-06 15:12 ` Peter Zijlstra
2012-09-06 21:35 ` Paul E. McKenney
2012-09-06 21:57 ` Steven Rostedt
2012-09-06 22:11 ` Paul E. McKenney
2012-08-30 18:56 ` [PATCH tip/core/rcu 15/15] kmemleak: Replace list_for_each_continue_rcu with new interface Paul E. McKenney
2012-08-31 18:55 ` Josh Triplett
2012-09-04 23:41 ` Paul E. McKenney
2012-08-31 16:49 ` [PATCH tip/core/rcu 01/15] rcu: Add PROVE_RCU_DELAY to provoke difficult races Josh Triplett
2012-09-04 22:36 ` Paul E. McKenney
2012-09-06 14:38 ` Peter Zijlstra
2012-09-06 20:51 ` Paul E. McKenney
2012-09-07 6:54 ` Peter Zijlstra
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