Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757272Ab3GEKZh (ORCPT ); Fri, 5 Jul 2013 06:25:37 -0400 Received: from www.linutronix.de ([62.245.132.108]:44270 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751222Ab3GEKZg (ORCPT ); Fri, 5 Jul 2013 06:25:36 -0400 Date: Fri, 5 Jul 2013 12:25:34 +0200 (CEST) From: Thomas Gleixner To: David Vrabel cc: Ingo Molnar , "H. Peter Anvin" , LKML , konrad.wilk@oracle.com, john.stultz@linaro.org, xen-devel@lists.xen.org, Artem Savkov Subject: Re: [tip:timers/core] hrtimers: Support resuming with two or more CPUs online (but stopped) In-Reply-To: <51D69ACF.9020001@citrix.com> Message-ID: References: <1372329348-20841-2-git-send-email-david.vrabel@citrix.com> <20130705093003.GA4033@cpv436-motbuntu> <51D69ACF.9020001@citrix.com> User-Agent: Alpine 2.02 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001,URIBL_BLOCKED=0.001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 7987 Lines: 175 On Fri, 5 Jul 2013, David Vrabel wrote: You failed to CC Artem :( > On 05/07/13 10:30, Artem Savkov wrote: > > This commit brings up a warning about a potential deadlock in > > smp_call_function_many() discussed previously: > > https://lkml.org/lkml/2013/4/18/546 > > Can we just avoid the wait in clock_was_set()? Something like this? > > 8<------------------------------------------------------ > hrtimers: do not wait for other CPUs in clock_was_set() > > Calling on_each_cpu() and waiting in a softirq causes a WARNing about > a potential deadlock. > > Because hrtimers are per-CPU, it is sufficient to ensure that all > other CPUs' timers are reprogrammed as soon as possible and before the > next softirq on that CPU. There is no need to wait for this to be > complete on all CPUs. > > on_each_cpu() works by IPIing all CPUs which will ensure > retrigger_next_event() will be called as earlier as possible and > before the next softirq. > > Signed-off-by: David Vrabel > --- > kernel/hrtimer.c | 2 +- > 1 files changed, 1 insertions(+), 1 deletions(-) > > diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c > index e86827e..fd5d391 100644 > --- a/kernel/hrtimer.c > +++ b/kernel/hrtimer.c > @@ -766,7 +766,7 @@ void clock_was_set(void) > { > #ifdef CONFIG_HIGH_RES_TIMERS > /* Retrigger the CPU local events everywhere */ > - on_each_cpu(retrigger_next_event, NULL, 1); > + on_each_cpu(retrigger_next_event, NULL, 0); > #endif > timerfd_clock_was_set(); > } > -- > 1.7.2.5 > > > > > > [ 4363.082047] PM: Restoring platform NVS memory > > [ 4363.082471] ------------[ cut here ]------------ > > [ 4363.083800] WARNING: CPU: 0 PID: 3977 at kernel/smp.c:385 smp_call_function_many+0xbd/0x2c0() > > [ 4363.085789] Modules linked in: > > [ 4363.086542] CPU: 0 PID: 3977 Comm: pm-suspend Tainted: G W 3.10.0-next-20130705 #126 > > [ 4363.088634] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2007 > > [ 4363.090402] 0000000000000181 ffff88001f403d98 ffffffff81d2e2b7 ffffffff821cdb2e > > [ 4363.092366] 0000000000000000 ffff88001f403dd8 ffffffff810a278c ffff88001f403dd8 > > [ 4363.094215] 0000000000000000 0000000000000000 0000000000000000 ffffffff82561898 > > [ 4363.096094] Call Trace: > > [ 4363.096656] [] dump_stack+0x59/0x82 > > [ 4363.098259] [] warn_slowpath_common+0x8c/0xc0 > > [ 4363.099762] [] warn_slowpath_null+0x1a/0x20 > > [ 4363.100925] [] smp_call_function_many+0xbd/0x2c0 > > [ 4363.101937] [] ? trace_hardirqs_on+0xd/0x10 > > [ 4363.102870] [] ? hrtimer_wakeup+0x30/0x30 > > [ 4363.103737] [] smp_call_function+0x3b/0x50 > > [ 4363.104609] [] ? hrtimer_wakeup+0x30/0x30 > > [ 4363.105455] [] on_each_cpu+0x3b/0x120 > > [ 4363.106249] [] clock_was_set+0x1c/0x30 > > [ 4363.107168] [] run_hrtimer_softirq+0x2c/0x40 > > [ 4363.108055] [] __do_softirq+0x216/0x450 > > [ 4363.108865] [] irq_exit+0x77/0xb0 > > [ 4363.109618] [] smp_apic_timer_interrupt+0x4a/0x60 > > [ 4363.110569] [] apic_timer_interrupt+0x72/0x80 > > [ 4363.111467] [] ? mark_held_locks+0x134/0x160 > > [ 4363.112481] [] ? arch_suspend_enable_irqs+0x2f/0x40 > > [ 4363.113457] [] ? arch_suspend_enable_irqs+0xe/0x40 > > [ 4363.113910] [] suspend_enter+0x1d1/0x270 > > [ 4363.114320] [] suspend_devices_and_enter+0x1a4/0x390 > > [ 4363.114887] [] enter_state+0xf4/0x150 > > [ 4363.115288] [] pm_suspend+0x1b/0x70 > > [ 4363.115662] [] state_store+0xeb/0xf0 > > [ 4363.116055] [] kobj_attr_store+0x17/0x20 > > [ 4363.116468] [] sysfs_write_file+0xb3/0x100 > > [ 4363.116890] [] vfs_write+0xda/0x170 > > [ 4363.117274] [] SyS_write+0x62/0xa0 > > [ 4363.117645] [] ? trace_hardirqs_on_thunk+0x3a/0x3f > > [ 4363.118118] [] system_call_fastpath+0x16/0x1b > > [ 4363.118558] ---[ end trace 87cc49a77badea1e ]--- > > [ 4363.119093] Enabling non-boot CPUs ... > > > > > > On Fri, Jun 28, 2013 at 02:18:37PM -0700, tip-bot for David Vrabel wrote: > >> Commit-ID: 7c4c3a0f18ba57ea2a2985034532303d2929902a > >> Gitweb: http://git.kernel.org/tip/7c4c3a0f18ba57ea2a2985034532303d2929902a > >> Author: David Vrabel > >> AuthorDate: Thu, 27 Jun 2013 11:35:44 +0100 > >> Committer: Thomas Gleixner > >> CommitDate: Fri, 28 Jun 2013 23:15:06 +0200 > >> > >> hrtimers: Support resuming with two or more CPUs online (but stopped) > >> > >> hrtimers_resume() only reprograms the timers for the current CPU as it > >> assumes that all other CPUs are offline at this point in the resume > >> process. If other CPUs are online then their timers will not be > >> corrected and they may fire at the wrong time. > >> > >> When running as a Xen guest, this assumption is not true. Non-boot > >> CPUs are only stopped with IRQs disabled instead of offlining them. > >> This is a performance optimization as disabling the CPUs would add an > >> unacceptable amount of additional downtime during a live migration (> > >> 200 ms for a 4 VCPU guest). > >> > >> hrtimers_resume() cannot call on_each_cpu(retrigger_next_event,...) > >> as the other CPUs will be stopped with IRQs disabled. Instead, defer > >> the call to the next softirq. > >> > >> [ tglx: Separated the xen change out ] > >> > >> Signed-off-by: David Vrabel > >> Cc: Konrad Rzeszutek Wilk > >> Cc: John Stultz > >> Cc: > >> Link: http://lkml.kernel.org/r/1372329348-20841-2-git-send-email-david.vrabel@citrix.com > >> Signed-off-by: Thomas Gleixner > >> --- > >> kernel/hrtimer.c | 15 ++++++++++++--- > >> 1 file changed, 12 insertions(+), 3 deletions(-) > >> > >> diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c > >> index fd4b13b..e86827e 100644 > >> --- a/kernel/hrtimer.c > >> +++ b/kernel/hrtimer.c > >> @@ -773,15 +773,24 @@ void clock_was_set(void) > >> > >> /* > >> * During resume we might have to reprogram the high resolution timer > >> - * interrupt (on the local CPU): > >> + * interrupt on all online CPUs. However, all other CPUs will be > >> + * stopped with IRQs interrupts disabled so the clock_was_set() call > >> + * must be deferred to the softirq. > >> + * > >> + * The one-shot timer has already been programmed to fire immediately > >> + * (see tick_resume_oneshot()) and this interrupt will trigger the > >> + * softirq to run early enough to correctly reprogram the timers on > >> + * all CPUs. > >> */ > >> void hrtimers_resume(void) > >> { > >> + struct hrtimer_cpu_base *cpu_base = &__get_cpu_var(hrtimer_bases); > >> + > >> WARN_ONCE(!irqs_disabled(), > >> KERN_INFO "hrtimers_resume() called with IRQs enabled!"); > >> > >> - retrigger_next_event(NULL); > >> - timerfd_clock_was_set(); > >> + cpu_base->clock_was_set = 1; > >> + __raise_softirq_irqoff(HRTIMER_SOFTIRQ); > >> } > >> > >> static inline void timer_stats_hrtimer_set_start_info(struct hrtimer *timer) > >> -- > >> 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/ > >> > > > > -- 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/