linux-kernel - [RFC PATCH v5 15/16] watchdog: Expose lockup_detector

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Date:   Tue,  4 May 2021 12:05:25 -0700
From:   Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...e.de>
Cc:     "H. Peter Anvin" <hpa@...or.com>, Ashok Raj <ashok.raj@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>,
        Nicholas Piggin <npiggin@...il.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Stephane Eranian <eranian@...gle.com>,
        Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Ricardo Neri <ricardo.neri@...el.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org,
        Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
        Andi Kleen <andi.kleen@...el.com>,
        linuxppc-dev@...ts.ozlabs.org
Subject: [RFC PATCH v5 15/16] watchdog: Expose lockup_detector_reconfigure()

When there are more than one implementation of the NMI watchdog, there may
be situations in which switching from one to another is needed. For
if the time-stamp counter becomes unstable, the HPET-based NMI watchdog
an no longer be used.

Switching to another hardlockup detector can be done cleanly by updating
the arch-specific stub and then reconfiguring the whole lockup detector.
Expose lockup_detector_reconfigure() to achieve this goal.

Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: Ashok Raj <ashok.raj@...el.com>
Cc: Andi Kleen <andi.kleen@...el.com>
Cc: Tony Luck <tony.luck@...el.com>
Cc: Nicholas Piggin <npiggin@...il.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Stephane Eranian <eranian@...gle.com>
Cc: Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
Cc: "Ravi V. Shankar" <ravi.v.shankar@...el.com>
Cc: x86@...nel.org
Cc: linuxppc-dev@...ts.ozlabs.org
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
---
Changes since v4:
 * Switching to the perf-based lockup detector under the hood is hacky.
   Instead, reconfigure the whole lockup detector.

Changes since v3:
 * None

Changes since v2:
 * Introduced this patch.

Changes since v1:
 * N/A
---
 include/linux/nmi.h | 2 ++
 kernel/watchdog.c   | 4 ++--
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/include/linux/nmi.h b/include/linux/nmi.h
index cf12380e51b3..73827a477288 100644
--- a/include/linux/nmi.h
+++ b/include/linux/nmi.h
@@ -16,6 +16,7 @@ void lockup_detector_init(void);
 void lockup_detector_soft_poweroff(void);
 void lockup_detector_cleanup(void);
 bool is_hardlockup(void);
+void lockup_detector_reconfigure(void);
 
 extern int watchdog_user_enabled;
 extern int nmi_watchdog_user_enabled;
@@ -37,6 +38,7 @@ extern int sysctl_hardlockup_all_cpu_backtrace;
 static inline void lockup_detector_init(void) { }
 static inline void lockup_detector_soft_poweroff(void) { }
 static inline void lockup_detector_cleanup(void) { }
+static inline void lockup_detector_reconfigure(void) { }
 #endif /* !CONFIG_LOCKUP_DETECTOR */
 
 #ifdef CONFIG_SOFTLOCKUP_DETECTOR
diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 4615064ee282..96f06938dc83 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -531,7 +531,7 @@ int lockup_detector_offline_cpu(unsigned int cpu)
 	return 0;
 }
 
-static void lockup_detector_reconfigure(void)
+void lockup_detector_reconfigure(void)
 {
 	cpus_read_lock();
 	watchdog_nmi_stop();
@@ -577,7 +577,7 @@ static __init void lockup_detector_setup(void)
 }
 
 #else /* CONFIG_SOFTLOCKUP_DETECTOR */
-static void lockup_detector_reconfigure(void)
+void lockup_detector_reconfigure(void)
 {
 	cpus_read_lock();
 	watchdog_nmi_stop();
-- 
2.17.1