linux-kernel - [tip:core/urgent] smpboot/threads, watchdog/core: Avoid runtime allocation

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Date:   Thu, 14 Sep 2017 03:45:29 -0700
From:   tip-bot for Thomas Gleixner <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
        peterz@...radead.org, cmetcalf@...lanox.com, bp@...en8.de,
        uobergfe@...hat.com, hpa@...or.com, tglx@...utronix.de,
        npiggin@...il.com, bigeasy@...utronix.de, dzickus@...hat.com,
        mingo@...nel.org, akpm@...ux-foundation.org
Subject: [tip:core/urgent] smpboot/threads, watchdog/core: Avoid runtime
 allocation

Commit-ID:  0d85923c7a81719567311ba0eae8ecb2efd4c8a0
Gitweb:     http://git.kernel.org/tip/0d85923c7a81719567311ba0eae8ecb2efd4c8a0
Author:     Thomas Gleixner <tglx@...utronix.de>
AuthorDate: Tue, 12 Sep 2017 21:37:09 +0200
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Thu, 14 Sep 2017 11:41:06 +0200

smpboot/threads, watchdog/core: Avoid runtime allocation

smpboot_update_cpumask_threads_percpu() allocates a temporary cpumask at
runtime. This is suboptimal because the call site needs more code size for
proper error handling than a statically allocated temporary mask requires
data size.

Add static temporary cpumask. The function is globaly serialized, so no
further protection required.

Remove the half baken error handling in the watchdog code and get rid of
the export as there are no in tree modular users of that function.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Reviewed-by: Don Zickus <dzickus@...hat.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Chris Metcalf <cmetcalf@...lanox.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Nicholas Piggin <npiggin@...il.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Sebastian Siewior <bigeasy@...utronix.de>
Cc: Ulrich Obergfell <uobergfe@...hat.com>
Link: http://lkml.kernel.org/r/20170912194147.297288838@linutronix.de
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 include/linux/smpboot.h |  4 ++--
 kernel/smpboot.c        | 22 +++++++---------------
 kernel/watchdog.c       | 21 +++++----------------
 3 files changed, 14 insertions(+), 33 deletions(-)

diff --git a/include/linux/smpboot.h b/include/linux/smpboot.h
index 12910cf..c149aa7 100644
--- a/include/linux/smpboot.h
+++ b/include/linux/smpboot.h
@@ -55,7 +55,7 @@ smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread)
 }
 
 void smpboot_unregister_percpu_thread(struct smp_hotplug_thread *plug_thread);
-int smpboot_update_cpumask_percpu_thread(struct smp_hotplug_thread *plug_thread,
-					 const struct cpumask *);
+void smpboot_update_cpumask_percpu_thread(struct smp_hotplug_thread *plug_thread,
+					  const struct cpumask *);
 
 #endif
diff --git a/kernel/smpboot.c b/kernel/smpboot.c
index 1d71c05..ed7507b 100644
--- a/kernel/smpboot.c
+++ b/kernel/smpboot.c
@@ -344,39 +344,31 @@ EXPORT_SYMBOL_GPL(smpboot_unregister_percpu_thread);
  * by the client, but only by calling this function.
  * This function can only be called on a registered smp_hotplug_thread.
  */
-int smpboot_update_cpumask_percpu_thread(struct smp_hotplug_thread *plug_thread,
-					 const struct cpumask *new)
+void smpboot_update_cpumask_percpu_thread(struct smp_hotplug_thread *plug_thread,
+					  const struct cpumask *new)
 {
 	struct cpumask *old = plug_thread->cpumask;
-	cpumask_var_t tmp;
+	static struct cpumask tmp;
 	unsigned int cpu;
 
-	if (!alloc_cpumask_var(&tmp, GFP_KERNEL))
-		return -ENOMEM;
-
 	get_online_cpus();
 	mutex_lock(&smpboot_threads_lock);
 
 	/* Park threads that were exclusively enabled on the old mask. */
-	cpumask_andnot(tmp, old, new);
-	for_each_cpu_and(cpu, tmp, cpu_online_mask)
+	cpumask_andnot(&tmp, old, new);
+	for_each_cpu_and(cpu, &tmp, cpu_online_mask)
 		smpboot_park_thread(plug_thread, cpu);
 
 	/* Unpark threads that are exclusively enabled on the new mask. */
-	cpumask_andnot(tmp, new, old);
-	for_each_cpu_and(cpu, tmp, cpu_online_mask)
+	cpumask_andnot(&tmp, new, old);
+	for_each_cpu_and(cpu, &tmp, cpu_online_mask)
 		smpboot_unpark_thread(plug_thread, cpu);
 
 	cpumask_copy(old, new);
 
 	mutex_unlock(&smpboot_threads_lock);
 	put_online_cpus();
-
-	free_cpumask_var(tmp);
-
-	return 0;
 }
-EXPORT_SYMBOL_GPL(smpboot_update_cpumask_percpu_thread);
 
 static DEFINE_PER_CPU(atomic_t, cpu_hotplug_state) = ATOMIC_INIT(CPU_POST_DEAD);
 
diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index cedf45a..8935a3a 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -787,31 +787,20 @@ out:
 	return err;
 }
 
-static int watchdog_update_cpus(void)
+static void watchdog_update_cpus(void)
 {
-	if (IS_ENABLED(CONFIG_SOFTLOCKUP_DETECTOR)) {
-		return smpboot_update_cpumask_percpu_thread(&watchdog_threads,
-							    &watchdog_cpumask);
+	if (IS_ENABLED(CONFIG_SOFTLOCKUP_DETECTOR) && watchdog_running) {
+		smpboot_update_cpumask_percpu_thread(&watchdog_threads,
+						     &watchdog_cpumask);
 		__lockup_detector_cleanup();
 	}
-	return 0;
 }
 
 static void proc_watchdog_cpumask_update(void)
 {
 	/* Remove impossible cpus to keep sysctl output clean. */
 	cpumask_and(&watchdog_cpumask, &watchdog_cpumask, cpu_possible_mask);
-
-	if (watchdog_running) {
-		/*
-		 * Failure would be due to being unable to allocate a
-		 * temporary cpumask, so we are likely not in a position to
-		 * do much else to make things better.
-		 */
-		if (watchdog_update_cpus() != 0)
-			pr_err("cpumask update failed\n");
-	}
-
+	watchdog_update_cpus();
 	watchdog_nmi_reconfigure();
 }