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From: Thomas Gleixner <tglx@linutronix.de>
To: Michael Ellerman <mpe@ellerman.id.au>
Cc: LKML <linux-kernel@vger.kernel.org>,
	Ingo Molnar <mingo@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Borislav Petkov <bp@alien8.de>,
	Andrew Morton <akpm@linux-foundation.org>,
	Sebastian Siewior <bigeasy@linutronix.de>,
	Nicholas Piggin <npiggin@gmail.com>,
	Don Zickus <dzickus@redhat.com>,
	Chris Metcalf <cmetcalf@mellanox.com>,
	Ulrich Obergfell <uobergfe@redhat.com>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	linuxppc-dev@lists.ozlabs.org
Subject: Re: [patch V2 22/29] lockup_detector: Make watchdog_nmi_reconfigure() two stage
Date: Tue, 3 Oct 2017 08:50:59 +0200 (CEST)
Message-ID: <alpine.DEB.2.20.1710030848210.2281@nanos> (raw)
In-Reply-To: <87d165dqew.fsf@concordia.ellerman.id.au>

On Tue, 3 Oct 2017, Michael Ellerman wrote:
> Hi Thomas,
> Unfortunately this is hitting the WARN_ON in start_wd_cpu() on powerpc
> because we're calling it multiple times for the boot CPU.
> 
> The first call is via:
> 
>   start_wd_on_cpu+0x80/0x2f0
>   watchdog_nmi_reconfigure+0x124/0x170
>   softlockup_reconfigure_threads+0x110/0x130
>   lockup_detector_init+0xbc/0xe0
>   kernel_init_freeable+0x18c/0x37c
>   kernel_init+0x2c/0x160
>   ret_from_kernel_thread+0x5c/0xbc
> 
> And then again via the CPU hotplug registration:
> 
>   start_wd_on_cpu+0x80/0x2f0
>   cpuhp_invoke_callback+0x194/0x620
>   cpuhp_thread_fun+0x7c/0x1b0
>   smpboot_thread_fn+0x290/0x2a0
>   kthread+0x168/0x1b0
>   ret_from_kernel_thread+0x5c/0xbc
> 
> 
> The first call is new because previously watchdog_nmi_reconfigure()
> wasn't called from softlockup_reconfigure_threads().

Hmm, don't you have the same problem with CPU hotplug or do you just get
lucky because the hotplug callback in your code is ordered vs. the
softlockup thread hotplug callback in a way that this does not hit?

> I'm not sure what the easiest fix is. One option would be to just drop
> the WARN_ON, it's just there for paranoia AFAICS.

The straight forward way is to make use of the new probe function. Patch
below.

Thanks,

	tglx

8<------------------
--- a/arch/powerpc/kernel/watchdog.c
+++ b/arch/powerpc/kernel/watchdog.c
@@ -375,20 +375,18 @@ void watchdog_nmi_start(void)
 /*
  * This runs after lockup_detector_init() which sets up watchdog_cpumask.
  */
-static int __init powerpc_watchdog_init(void)
+int __init watchdog_nmi_probe(void)
 {
 	int err;
 
-	watchdog_calc_timeouts();
-
-	err = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "powerpc/watchdog:online",
-				start_wd_on_cpu, stop_wd_on_cpu);
+	err = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
+					"powerpc/watchdog:online",
+					start_wd_on_cpu, stop_wd_on_cpu);
 	if (err < 0)
 		pr_warn("Watchdog could not be initialized");
 
 	return 0;
 }
-arch_initcall(powerpc_watchdog_init);
 
 static void handle_backtrace_ipi(struct pt_regs *regs)
 {
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -608,7 +608,6 @@ static inline int watchdog_park_threads(
 static inline void watchdog_unpark_threads(void) { }
 static inline int watchdog_enable_all_cpus(void) { return 0; }
 static inline void watchdog_disable_all_cpus(void) { }
-static inline void softlockup_init_threads(void) { }
 static void softlockup_reconfigure_threads(void)
 {
 	cpus_read_lock();
@@ -617,6 +616,10 @@ static void softlockup_reconfigure_threa
 	watchdog_nmi_start();
 	cpus_read_unlock();
 }
+static inline void softlockup_init_threads(void)
+{
+	softlockup_reconfigure_threads();
+}
 #endif /* !CONFIG_SOFTLOCKUP_DETECTOR */
 
 static void __lockup_detector_cleanup(void)

  reply index

Thread overview: 77+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-09-12 19:36 [patch V2 00/29] lockup_detector: Cure hotplug deadlocks and replace duct tape Thomas Gleixner
2017-09-12 19:36 ` [patch V2 01/29] hardlockup_detector: Provide interface to stop/restart perf events Thomas Gleixner
2017-09-14 10:40   ` [tip:core/urgent] watchdog/hardlockup: " tip-bot for Peter Zijlstra
2017-09-12 19:36 ` [patch V2 02/29] perf/x86/intel: Sanitize PMU HT bug workaround Thomas Gleixner
2017-09-14 10:40   ` [tip:core/urgent] perf/x86/intel, watchdog/core: " tip-bot for Peter Zijlstra
2017-09-12 19:36 ` [patch V2 03/29] lockup_detector: Provide interface to stop from poweroff() Thomas Gleixner
2017-09-14 10:40   ` [tip:core/urgent] watchdog/core: " tip-bot for Thomas Gleixner
2017-09-12 19:36 ` [patch V2 04/29] parisc: Use lockup_detector_stop() Thomas Gleixner
2017-09-14  8:59   ` Helge Deller
2017-09-14 13:46     ` Don Zickus
2017-09-14 10:41   ` [tip:core/urgent] parisc, watchdog/core: " tip-bot for Thomas Gleixner
2017-09-12 19:36 ` [patch V2 05/29] lockup_detector: Remove broken suspend/resume interfaces Thomas Gleixner
2017-09-14 10:41   ` [tip:core/urgent] watchdog/core: " tip-bot for Thomas Gleixner
2017-09-12 19:37 ` [patch V2 06/29] lockup_detector: Rework cpu hotplug locking Thomas Gleixner
2017-09-14 10:41   ` [tip:core/urgent] watchdog/core: Rework CPU " tip-bot for Thomas Gleixner
2017-09-12 19:37 ` [patch V2 07/29] lockup_detector: Rename watchdog_proc_mutex Thomas Gleixner
2017-09-14 10:42   ` [tip:core/urgent] watchdog/core: " tip-bot for Thomas Gleixner
2017-09-12 19:37 ` [patch V2 08/29] lockup_detector: Mark hardlockup_detector_disable() __init Thomas Gleixner
2017-09-14 10:42   ` [tip:core/urgent] watchdog/core: " tip-bot for Thomas Gleixner
2017-09-12 19:37 ` [patch V2 09/29] lockup_detector/perf: Remove broken self disable on failure Thomas Gleixner
2017-09-14 10:43   ` [tip:core/urgent] watchdog/hardlockup/perf: " tip-bot for Thomas Gleixner
2017-09-12 19:37 ` [patch V2 10/29] lockup_detector/perf: Prevent cpu hotplug deadlock Thomas Gleixner
2017-09-14 10:43   ` [tip:core/urgent] watchdog/hardlockup/perf: Prevent CPU " tip-bot for Thomas Gleixner
2017-09-12 19:37 ` [patch V2 11/29] lockup_detector: Remove park_in_progress obfuscation Thomas Gleixner
2017-09-12 19:37 ` [patch V2 12/29] lockup_detector: Cleanup stub functions Thomas Gleixner
2017-09-14 10:44   ` [tip:core/urgent] watchdog/core: Clean up " tip-bot for Thomas Gleixner
2017-09-12 19:37 ` [patch V2 13/29] lockup_detector: Cleanup the ifdef maze Thomas Gleixner
2017-09-14 10:44   ` [tip:core/urgent] watchdog/core: Clean up the #ifdef maze tip-bot for Thomas Gleixner
2017-09-12 19:37 ` [patch V2 14/29] lockup_detector: Split out cpumask write function Thomas Gleixner
2017-09-14 10:45   ` [tip:core/urgent] watchdog/core: " tip-bot for Thomas Gleixner
2017-09-12 19:37 ` [patch V2 15/29] smpboot/threads: Avoid runtime allocation Thomas Gleixner
2017-09-14 10:45   ` [tip:core/urgent] smpboot/threads, watchdog/core: " tip-bot for Thomas Gleixner
2017-09-12 19:37 ` [patch V2 16/29] lockup_detector: Create new thread handling infrastructure Thomas Gleixner
2017-09-14 10:45   ` [tip:core/urgent] watchdog/core: " tip-bot for Thomas Gleixner
2017-09-12 19:37 ` [patch V2 17/29] lockup_detector: Get rid of the thread teardown/setup dance Thomas Gleixner
2017-09-14 10:46   ` [tip:core/urgent] watchdog/core: " tip-bot for Thomas Gleixner
2017-09-12 19:37 ` [patch V2 18/29] lockup_detector: Further simplify sysctl handling Thomas Gleixner
2017-09-14 10:46   ` [tip:core/urgent] watchdog/core: " tip-bot for Thomas Gleixner
2017-09-12 19:37 ` [patch V2 19/29] lockup_detector: Cleanup header mess Thomas Gleixner
2017-09-14 10:47   ` [tip:core/urgent] watchdog/core: Clean up " tip-bot for Thomas Gleixner
2017-09-12 19:37 ` [patch V2 20/29] lockup_detector/sysctl: Get rid of the ifdeffery Thomas Gleixner
2017-09-14 10:47   ` [tip:core/urgent] watchdog/sysctl: Get rid of the #ifdeffery tip-bot for Thomas Gleixner
2017-09-12 19:37 ` [patch V2 21/29] lockup_detector: Cleanup sysctl variable name space Thomas Gleixner
2017-09-14 10:47   ` [tip:core/urgent] watchdog/sysctl: Clean up " tip-bot for Thomas Gleixner
2017-09-12 19:37 ` [patch V2 22/29] lockup_detector: Make watchdog_nmi_reconfigure() two stage Thomas Gleixner
2017-09-14 10:48   ` [tip:core/urgent] watchdog/core, powerpc: " tip-bot for Thomas Gleixner
2017-10-03  0:29   ` [patch V2 22/29] lockup_detector: " Michael Ellerman
2017-10-03  6:50     ` Thomas Gleixner [this message]
2017-10-03  7:04       ` Thomas Gleixner
2017-10-03 10:01         ` Nicholas Piggin
2017-10-03 10:56           ` Thomas Gleixner
2017-10-03 11:36       ` Michael Ellerman
2017-10-03 12:13         ` Thomas Gleixner
2017-10-03 13:20           ` Thomas Gleixner
2017-10-03 19:27             ` Thomas Gleixner
2017-10-04  5:53               ` Michael Ellerman
2017-10-05 16:17               ` Don Zickus
2017-09-12 19:37 ` [patch V2 23/29] lockup_detector: Get rid of the racy update loop Thomas Gleixner
2017-09-14 10:48   ` [tip:core/urgent] watchdog/core: " tip-bot for Thomas Gleixner
2017-09-12 19:37 ` [patch V2 24/29] lockup_detector/perf: Implement init time perf validation Thomas Gleixner
2017-09-14 10:48   ` [tip:core/urgent] watchdog/hardlockup/perf: " tip-bot for Thomas Gleixner
2017-09-12 19:37 ` [patch V2 25/29] lockup_detector: Implement init time detection of perf Thomas Gleixner
2017-09-13 18:02   ` Don Zickus
2017-09-13 18:05     ` Thomas Gleixner
2017-09-14  5:27       ` Ingo Molnar
2017-09-14 10:49   ` [tip:core/urgent] watchdog/hardlockup/perf: " tip-bot for Thomas Gleixner
2017-09-12 19:37 ` [patch V2 26/29] lockup_detector/perf: Implement CPU enable replacement Thomas Gleixner
2017-09-14 10:49   ` [tip:core/urgent] watchdog/hardlockup/perf: " tip-bot for Thomas Gleixner
2017-09-12 19:37 ` [patch V2 27/29] lockup_detector: Use new perf CPU enable mechanism Thomas Gleixner
2017-09-14 10:50   ` [tip:core/urgent] watchdog/hardlockup/perf: " tip-bot for Thomas Gleixner
2017-09-12 19:37 ` [patch V2 28/29] lockup_detector/perf: Simplify deferred event destroy Thomas Gleixner
2017-09-14 10:50   ` [tip:core/urgent] watchdog/hardlockup/perf: " tip-bot for Thomas Gleixner
2017-09-12 19:37 ` [patch V2 29/29] lockup_detector: Cleanup hotplug locking mess Thomas Gleixner
2017-09-14 10:50   ` [tip:core/urgent] watchdog/hardlockup: Clean up " tip-bot for Thomas Gleixner
2017-09-13 18:06 ` [patch V2 00/29] lockup_detector: Cure hotplug deadlocks and replace duct tape Don Zickus
2017-09-14  5:27   ` Ingo Molnar
2017-09-14  8:11   ` Thomas Gleixner

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