lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
Open Source and information security mailing list archives
| ||
|
Message-ID: <20140721181612.GJ8690@linux.vnet.ibm.com> Date: Mon, 21 Jul 2014 11:16:12 -0700 From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> To: Frederic Weisbecker <fweisbec@...il.com> Cc: LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...nel.org>, Peter Zijlstra <peterz@...radead.org>, Steven Rostedt <rostedt@...dmis.org>, Thomas Gleixner <tglx@...utronix.de>, Viresh Kumar <viresh.kumar@...aro.org> Subject: Re: [PATCH 03/10] rcu: Kick full dynticks CPU on extended grace period with a void IRQ On Sat, Jul 19, 2014 at 02:44:14AM +0200, Frederic Weisbecker wrote: > When a full dynticks CPU stays for too long in the kernel, it may fail > to report quiescent states due to it missing ticks and therefore it can > delay the completion of grace periods. > > A way to solve this is to send an IPI to the incriminated CPU such that > it can check rcu_needs_cpu() and reschedule some ticks accordingly to > poll again on quiescent states reports. > > This is what we try to achieve while calling rcu_kick_nohz_cpu() but it > has no effect because we trigger a scheduler IPI which is actually a > no-op when not used for scheduler internal purpose, ie: it doesn't call > irq_exit() when not used for remote wakeup or other specifics. > > No need to tweak the scheduler IPI further though. Lets keep it clean > of external noise and use an empty IPI instead. We hereby get sure that > we will call irq_exit() on the target without much overhead nor added > noise on scheduler fast path. > > Cc: Ingo Molnar <mingo@...nel.org> > Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com> > Cc: Peter Zijlstra <peterz@...radead.org> > Cc: Steven Rostedt <rostedt@...dmis.org> > Cc: Thomas Gleixner <tglx@...utronix.de> > Cc: Viresh Kumar <viresh.kumar@...aro.org> > Signed-off-by: Frederic Weisbecker <fweisbec@...il.com> Reviewed-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com> > --- > kernel/rcu/tree_plugin.h | 8 +++++--- > 1 file changed, 5 insertions(+), 3 deletions(-) > > diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h > index cbc2c45..395c14d 100644 > --- a/kernel/rcu/tree_plugin.h > +++ b/kernel/rcu/tree_plugin.h > @@ -2401,14 +2401,16 @@ static bool init_nocb_callback_list(struct rcu_data *rdp) > * off. RCU will be paying attention to this CPU because it is in the > * kernel, but the CPU cannot be guaranteed to be executing the RCU state > * machine because the scheduling-clock tick has been disabled. Therefore, > - * if an adaptive-ticks CPU is failing to respond to the current grace > - * period and has not be idle from an RCU perspective, kick it. > + * if an full dynticks CPU is failing to respond to the current grace > + * period and has not be idle from an RCU perspective, kick it with a > + * void IRQ so that it can check that RCU needs its tick from rcu_needs_cpu() > + * on irq exit. > */ > static void rcu_kick_nohz_cpu(int cpu) > { > #ifdef CONFIG_NO_HZ_FULL > if (tick_nohz_full_cpu(cpu)) > - smp_send_reschedule(cpu); > + irq_work_void_on(cpu); > #endif /* #ifdef CONFIG_NO_HZ_FULL */ > } > > -- > 1.8.3.1 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@...r.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists