Messages in this thread Patch in this message | | | Date | Fri, 27 Mar 2020 10:53:11 +0800 | From | Boqun Feng <> | Subject | Re: [tip:smp/hotplug] cpu/hotplug: Abort disabling secondary CPUs if wakeup is pending |
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Hi Thomas and Pavankumar,
I have a question about this patch, please see below:
On Wed, Jun 12, 2019 at 05:34:08AM -0700, tip-bot for Pavankumar Kondeti wrote: > Commit-ID: a66d955e910ab0e598d7a7450cbe6139f52befe7 > Gitweb: https://git.kernel.org/tip/a66d955e910ab0e598d7a7450cbe6139f52befe7 > Author: Pavankumar Kondeti <pkondeti@codeaurora.org> > AuthorDate: Mon, 3 Jun 2019 10:01:03 +0530 > Committer: Thomas Gleixner <tglx@linutronix.de> > CommitDate: Wed, 12 Jun 2019 11:03:05 +0200 > > cpu/hotplug: Abort disabling secondary CPUs if wakeup is pending > > When "deep" suspend is enabled, all CPUs except the primary CPU are frozen > via CPU hotplug one by one. After all secondary CPUs are unplugged the > wakeup pending condition is evaluated and if pending the suspend operation > is aborted and the secondary CPUs are brought up again. > > CPU hotplug is a slow operation, so it makes sense to check for wakeup > pending in the freezer loop before bringing down the next CPU. This > improves the system suspend abort latency significantly. >
From the commit message, it makes sense to add the pm_wakeup_pending() check if freeze_secondary_cpus() is used for system suspend. However, freeze_secondary_cpus() is also used in kexec path on arm64:
kernel_kexec(): machine_shutdown(): disable_nonboot_cpus(): freeze_secondary_cpus()
, so I wonder whether the pm_wakeup_pending() makes sense in this situation? Because IIUC, in this case we want to reboot the system regardlessly, the pm_wakeup_pending() checking seems to be inappropriate then.
I'm asking this because I'm debugging a kexec failure on ARM64 guest on Hyper-V, and I got the BUG_ON() triggered:
[ 108.378016] kexec_core: Starting new kernel [ 108.378018] Disabling non-boot CPUs ... [ 108.378019] Wakeup pending. Abort CPU freeze [ 108.378020] Non-boot CPUs are not disabled [ 108.378049] ------------[ cut here ]------------ [ 108.378050] kernel BUG at arch/arm64/kernel/machine_kexec.c:154!
Thanks!
Regards, Boqun
> [ tglx: Massaged changelog and improved printk message ] > > Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org> > Signed-off-by: Thomas Gleixner <tglx@linutronix.de> > Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net> > Cc: Len Brown <len.brown@intel.com> > Cc: Pavel Machek <pavel@ucw.cz> > Cc: Josh Poimboeuf <jpoimboe@redhat.com> > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> > Cc: iri Kosina <jkosina@suse.cz> > Cc: Mukesh Ojha <mojha@codeaurora.org> > Cc: linux-pm@vger.kernel.org > Link: https://lkml.kernel.org/r/1559536263-16472-1-git-send-email-pkondeti@codeaurora.org > > --- > kernel/cpu.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/kernel/cpu.c b/kernel/cpu.c > index be82cbc11a8a..0778249cd49d 100644 > --- a/kernel/cpu.c > +++ b/kernel/cpu.c > @@ -1221,6 +1221,13 @@ int freeze_secondary_cpus(int primary) > for_each_online_cpu(cpu) { > if (cpu == primary) > continue; > + > + if (pm_wakeup_pending()) { > + pr_info("Wakeup pending. Abort CPU freeze\n"); > + error = -EBUSY; > + break; > + } > + > trace_suspend_resume(TPS("CPU_OFF"), cpu, true); > error = _cpu_down(cpu, 1, CPUHP_OFFLINE); > trace_suspend_resume(TPS("CPU_OFF"), cpu, false);
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