linux-kernel - [tip:core/urgent] watchdog/hardlockup: Clean up hotplug locking mess

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Date:   Thu, 14 Sep 2017 03:50:56 -0700
From:   tip-bot for Thomas Gleixner <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     uobergfe@...hat.com, akpm@...ux-foundation.org,
        peterz@...radead.org, mingo@...nel.org, tglx@...utronix.de,
        npiggin@...il.com, torvalds@...ux-foundation.org,
        dzickus@...hat.com, linux-kernel@...r.kernel.org,
        bigeasy@...utronix.de, cmetcalf@...lanox.com, bp@...en8.de,
        benh@...nel.crashing.org, mpe@...erman.id.au, hpa@...or.com
Subject: [tip:core/urgent] watchdog/hardlockup: Clean up hotplug locking
 mess

Commit-ID:  ab5fe3ff38ff9653490910cc71dbbedc95a86e41
Gitweb:     http://git.kernel.org/tip/ab5fe3ff38ff9653490910cc71dbbedc95a86e41
Author:     Thomas Gleixner <tglx@...utronix.de>
AuthorDate: Tue, 12 Sep 2017 21:37:23 +0200
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Thu, 14 Sep 2017 11:41:09 +0200

watchdog/hardlockup: Clean up hotplug locking mess

All watchdog thread related functions are delegated to the smpboot thread
infrastructure, which handles serialization against CPU hotplug correctly.

The sysctl interface is completely decoupled from anything which requires
CPU hotplug protection.

No need to protect the sysctl writes against cpu hotplug anymore. Remove it
and add the now required protection to the powerpc arch_nmi_watchdog
implementation.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Reviewed-by: Don Zickus <dzickus@...hat.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Chris Metcalf <cmetcalf@...lanox.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Michael Ellerman <mpe@...erman.id.au>
Cc: Nicholas Piggin <npiggin@...il.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Sebastian Siewior <bigeasy@...utronix.de>
Cc: Ulrich Obergfell <uobergfe@...hat.com>
Cc: linuxppc-dev@...ts.ozlabs.org
Link: http://lkml.kernel.org/r/20170912194148.418497420@linutronix.de
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/powerpc/kernel/watchdog.c | 2 ++
 kernel/watchdog.c              | 6 ------
 2 files changed, 2 insertions(+), 6 deletions(-)

diff --git a/arch/powerpc/kernel/watchdog.c b/arch/powerpc/kernel/watchdog.c
index 291af79..dfb0677 100644
--- a/arch/powerpc/kernel/watchdog.c
+++ b/arch/powerpc/kernel/watchdog.c
@@ -359,6 +359,7 @@ void watchdog_nmi_reconfigure(bool run)
 {
 	int cpu;
 
+	cpus_read_lock();
 	if (!run) {
 		for_each_cpu(cpu, &wd_cpus_enabled)
 			stop_wd_on_cpu(cpu);
@@ -367,6 +368,7 @@ void watchdog_nmi_reconfigure(bool run)
 		for_each_cpu_and(cpu, cpu_online_mask, &watchdog_cpumask)
 			start_wd_on_cpu(cpu);
 	}
+	cpus_read_unlock();
 }
 
 /*
diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 5eb1196..f6ef163 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -664,7 +664,6 @@ static int proc_watchdog_common(int which, struct ctl_table *table, int write,
 {
 	int err, old, *param = table->data;
 
-	cpu_hotplug_disable();
 	mutex_lock(&watchdog_mutex);
 
 	if (!write) {
@@ -681,7 +680,6 @@ static int proc_watchdog_common(int which, struct ctl_table *table, int write,
 			proc_watchdog_update();
 	}
 	mutex_unlock(&watchdog_mutex);
-	cpu_hotplug_enable();
 	return err;
 }
 
@@ -725,7 +723,6 @@ int proc_watchdog_thresh(struct ctl_table *table, int write,
 {
 	int err, old;
 
-	cpu_hotplug_disable();
 	mutex_lock(&watchdog_mutex);
 
 	old = READ_ONCE(watchdog_thresh);
@@ -735,7 +732,6 @@ int proc_watchdog_thresh(struct ctl_table *table, int write,
 		proc_watchdog_update();
 
 	mutex_unlock(&watchdog_mutex);
-	cpu_hotplug_enable();
 	return err;
 }
 
@@ -750,7 +746,6 @@ int proc_watchdog_cpumask(struct ctl_table *table, int write,
 {
 	int err;
 
-	cpu_hotplug_disable();
 	mutex_lock(&watchdog_mutex);
 
 	err = proc_do_large_bitmap(table, write, buffer, lenp, ppos);
@@ -758,7 +753,6 @@ int proc_watchdog_cpumask(struct ctl_table *table, int write,
 		proc_watchdog_update();
 
 	mutex_unlock(&watchdog_mutex);
-	cpu_hotplug_enable();
 	return err;
 }
 #endif /* CONFIG_SYSCTL */