From: Will Deacon <will.deacon@arm.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
linux-kernel@vger.kernel.org, rt@linuxtronix.de,
Mark Rutland <mark.rutland@arm.com>,
Russell King <linux@armlinux.org.uk>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 15/20] ARM/hw_breakpoint: Convert to hotplug state machine
Date: Fri, 18 Nov 2016 13:29:13 +0000 [thread overview]
Message-ID: <20161118132912.GM13470@arm.com> (raw)
In-Reply-To: <alpine.DEB.2.20.1611181401180.3615@nanos>
On Fri, Nov 18, 2016 at 02:11:58PM +0100, Thomas Gleixner wrote:
> On Fri, 18 Nov 2016, Will Deacon wrote:
> > On Thu, Nov 17, 2016 at 07:35:36PM +0100, Sebastian Andrzej Siewior wrote:
> > > @@ -1082,15 +1077,18 @@ static int __init arch_hw_breakpoint_init(void)
> > > register_undef_hook(&debug_reg_hook);
> > >
> > > /*
> > > - * Reset the breakpoint resources. We assume that a halting
> > > - * debugger will leave the world in a nice state for us.
> > > + * Register CPU notifier which resets the breakpoint resources. We
> > > + * assume that a halting debugger will leave the world in a nice state
> > > + * for us.
> > > */
> > > - on_each_cpu(reset_ctrl_regs, NULL, 1);
> > > + ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "arm/hw_breakpoint:online",
> > > + dbg_reset_online, NULL);
> >
> > I'm slightly unsure about this. The dbg_reset_online callback can execute
> > undefined instructions (unfortunately, there's no way to probe the presence
> > of some of the debug registers), so it absolutely has to run within the
> > register_undef_hook/unregister_undef_hook calls that are in this function.
> >
> > With this patch, I worry that the callback can be postponed to ONLINE time
> > for other CPUs, and then the kernel will panic.
>
> No. The flow is the following:
>
> register_undef_hook(&debug_reg_hook);
>
> ret = cpuhp_setup_state(.., dbg_reset_online, NULL);
> {
> for_each_online_cpu(cpu) {
> ret = call_on_cpu(cpu, dbg_reset_online);
> if (ret)
> return ret:
> }
> }
>
> unregister_undef_hook(&debug_reg_hook);
>
> The only difference to the current code is that the call is not invoked via
> a smp function call (on_each_cpu), it's pushed to the hotplug thread
> context of each cpu and executed there.
>
> But it's guaranteed that cpuhp_setup_state() will not return before the
> callback has been invoked on each online cpu.
Ok, that's good.
> If cpus are not yet online when that code is invoked, then it's the same
> behaviour as before. It will be invoked when the cpu comes online.
Just to check, but what stops a CPU from coming online between the call
to cpuhp_setup_state and the call to cpuhp_remove_state_nocalls in the
case of failure (debug_err_mask isn't empty)?
Will
next prev parent reply other threads:[~2016-11-18 13:30 UTC|newest]
Thread overview: 94+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-17 18:35 cpu hotplug: convert more drivers (batch #5) Sebastian Andrzej Siewior
2016-11-17 18:35 ` [PATCH 01/20] x86/mce/therm_throt: Convert to hotplug state machine Sebastian Andrzej Siewior
2016-11-21 15:46 ` [tip:smp/hotplug] " tip-bot for Sebastian Andrzej Siewior
2016-11-22 22:39 ` tip-bot for Sebastian Andrzej Siewior
2016-11-17 18:35 ` [PATCH 02/20] x86/cpuid: " Sebastian Andrzej Siewior
2016-11-21 15:47 ` [tip:smp/hotplug] " tip-bot for Sebastian Andrzej Siewior
2016-11-22 22:40 ` tip-bot for Sebastian Andrzej Siewior
2016-11-17 18:35 ` [PATCH 03/20] x86/msr: " Sebastian Andrzej Siewior
2016-11-21 15:48 ` [tip:smp/hotplug] " tip-bot for Sebastian Andrzej Siewior
2016-11-22 22:41 ` tip-bot for Sebastian Andrzej Siewior
2016-11-17 18:35 ` [PATCH 04/20] hwmon/coretemp: " Sebastian Andrzej Siewior
2016-11-20 22:30 ` [04/20] " Guenter Roeck
2016-11-21 22:35 ` Sebastian Andrzej Siewior
2016-11-21 15:56 ` [tip:smp/hotplug] " tip-bot for Sebastian Andrzej Siewior
2016-11-21 21:32 ` Guenter Roeck
2016-11-21 21:53 ` Thomas Gleixner
2016-11-17 18:35 ` [PATCH 05/20] hwmon/via-cputemp: Remove pointless CPU check on each CPU Sebastian Andrzej Siewior
2016-11-19 17:23 ` [05/20] " Guenter Roeck
2016-11-19 22:53 ` Sebastian Andrzej Siewior
2016-11-20 3:53 ` Guenter Roeck
2016-11-20 20:34 ` Sebastian Andrzej Siewior
2016-11-17 18:35 ` [PATCH 06/20] hwmon/via-cputemp: Convert to hotplug state machine Sebastian Andrzej Siewior
2016-11-18 15:09 ` [PATCH 06/20 v2] " Sebastian Andrzej Siewior
2016-11-23 15:29 ` [PATCH 06/20] " Guenter Roeck
2016-12-09 11:53 ` Thomas Gleixner
2016-12-09 18:17 ` Guenter Roeck
2016-12-09 18:27 ` Thomas Gleixner
2016-11-17 18:35 ` [PATCH 07/20] pci/xgene-msi: " Sebastian Andrzej Siewior
2016-11-21 15:48 ` [tip:smp/hotplug] PCI/xgene-msi: " tip-bot for Sebastian Andrzej Siewior
2016-11-22 22:42 ` tip-bot for Sebastian Andrzej Siewior
2016-11-17 18:35 ` [PATCH 08/20] powercap/intel_rapl: Add missing domain data update on hotplug Sebastian Andrzej Siewior
2016-11-21 15:49 ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2016-11-17 18:35 ` [PATCH 09/20] powercap/intel rapl: Convert to hotplug state machine Sebastian Andrzej Siewior
2016-11-21 15:49 ` [tip:smp/hotplug] " tip-bot for Sebastian Andrzej Siewior
2016-11-17 18:35 ` [PATCH 10/20] powercap/intel_rapl: Cleanup duplicated init code Sebastian Andrzej Siewior
2016-11-21 15:50 ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2016-11-17 18:35 ` [PATCH 11/20] watchdog/octeon: Convert to hotplug state machine Sebastian Andrzej Siewior
2016-11-21 15:50 ` [tip:smp/hotplug] " tip-bot for Sebastian Andrzej Siewior
2016-11-22 22:43 ` tip-bot for Sebastian Andrzej Siewior
2016-11-24 16:10 ` [11/20] " Guenter Roeck
2016-11-17 18:35 ` [PATCH 12/20] net/iucv: " Sebastian Andrzej Siewior
2016-11-21 15:51 ` [tip:smp/hotplug] " tip-bot for Sebastian Andrzej Siewior
2016-11-22 22:43 ` tip-bot for Sebastian Andrzej Siewior
2016-11-23 18:04 ` [PATCH 12/20] " Ursula Braun
2016-11-24 9:10 ` Sebastian Andrzej Siewior
2016-11-24 14:14 ` [PATCH 12/20 v2] " Sebastian Andrzej Siewior
2016-11-24 16:10 ` [PATCH] net/iucv: use explicit clean up labels in iucv_init() Sebastian Andrzej Siewior
2016-11-24 19:57 ` [tip:smp/hotplug] net/iucv: Use " tip-bot for Sebastian Andrzej Siewior
2016-11-28 16:24 ` [PATCH] net/iucv: use " David Miller
2016-11-28 16:31 ` Thomas Gleixner
2016-11-28 16:37 ` [tip:smp/hotplug] net/iucv: Use " tip-bot for Sebastian Andrzej Siewior
2016-11-17 18:35 ` [PATCH 13/20] sched/nohz: Convert to hotplug state machine Sebastian Andrzej Siewior
2016-11-21 15:51 ` [tip:smp/hotplug] " tip-bot for Sebastian Andrzej Siewior
2016-11-22 22:44 ` tip-bot for Sebastian Andrzej Siewior
2016-11-17 18:35 ` [PATCH 14/20] arm/bL_switcher: " Sebastian Andrzej Siewior
2016-11-21 15:52 ` [tip:smp/hotplug] " tip-bot for Sebastian Andrzej Siewior
2016-11-22 22:44 ` tip-bot for Sebastian Andrzej Siewior
2016-11-17 18:35 ` [PATCH 15/20] ARM/hw_breakpoint: " Sebastian Andrzej Siewior
2016-11-18 12:04 ` Will Deacon
2016-11-18 13:11 ` Thomas Gleixner
2016-11-18 13:29 ` Will Deacon [this message]
2016-11-18 13:42 ` Thomas Gleixner
2016-11-18 13:48 ` Will Deacon
2016-11-18 13:59 ` Thomas Gleixner
2016-11-18 14:11 ` Will Deacon
2016-11-21 15:52 ` [tip:smp/hotplug] " tip-bot for Sebastian Andrzej Siewior
2016-11-22 22:45 ` tip-bot for Sebastian Andrzej Siewior
2017-01-02 14:15 ` [PATCH 15/20] " Linus Walleij
2017-01-02 14:34 ` Linus Walleij
2017-01-02 15:00 ` Russell King - ARM Linux
2017-01-02 20:15 ` Linus Walleij
2017-01-03 9:33 ` Mark Rutland
2017-01-04 11:27 ` Sebastian Andrzej Siewior
2017-01-04 13:56 ` Mark Rutland
2017-01-04 14:32 ` Will Deacon
2017-01-05 15:57 ` Mark Rutland
2017-01-05 15:26 ` Linus Walleij
2017-01-05 17:14 ` Mark Rutland
2016-11-17 18:35 ` [PATCH 16/20] powerpc/sysfs: " Sebastian Andrzej Siewior
2016-11-21 15:53 ` [tip:smp/hotplug] " tip-bot for Sebastian Andrzej Siewior
2016-11-22 22:45 ` tip-bot for Sebastian Andrzej Siewior
2016-11-17 18:35 ` [PATCH 17/20] sparc/sysfs: " Sebastian Andrzej Siewior
2016-11-17 18:39 ` David Miller
2016-11-21 15:54 ` [tip:smp/hotplug] " tip-bot for Sebastian Andrzej Siewior
2016-11-22 22:46 ` tip-bot for Sebastian Andrzej Siewior
2016-11-17 18:35 ` [PATCH 18/20] x86/oprofile/nmi: Remove superfluous smp_function_call_single() Sebastian Andrzej Siewior
2016-11-21 15:54 ` [tip:smp/hotplug] " tip-bot for Anna-Maria Gleixner
2016-11-22 22:46 ` tip-bot for Anna-Maria Gleixner
2016-11-17 18:35 ` [PATCH 19/20] x86/oprofile/nmi: Convert to hotplug state machine Sebastian Andrzej Siewior
2016-11-21 15:55 ` [tip:smp/hotplug] " tip-bot for Sebastian Andrzej Siewior
2016-11-22 22:47 ` tip-bot for Sebastian Andrzej Siewior
2016-11-17 18:35 ` [PATCH 20/20] x86/pci/amd-bus: " Sebastian Andrzej Siewior
2016-11-21 15:55 ` [tip:smp/hotplug] " tip-bot for Sebastian Andrzej Siewior
2016-11-22 22:47 ` tip-bot for Sebastian Andrzej Siewior
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20161118132912.GM13470@arm.com \
--to=will.deacon@arm.com \
--cc=bigeasy@linutronix.de \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux@armlinux.org.uk \
--cc=mark.rutland@arm.com \
--cc=rt@linuxtronix.de \
--cc=tglx@linutronix.de \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).