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Patch "MIPS: SMP: Use a completion event to signal CPU up" has been added to the 4.9-stable tree

PATCH [email protected] 1 participant 1 message Nov 10, 2017

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This is a note to let you know that I've just added the patch titled

MIPS: SMP: Use a completion event to signal CPU up

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
mips-smp-use-a-completion-event-to-signal-cpu-up.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

Quoted 1 line

From a00eeede507c975087b7b8df8cf2c9f88ba285de Mon Sep 17 00:00:00 2001

From: Matt Redfearn <[email protected]>
Date: Fri, 4 Nov 2016 09:28:56 +0000
Subject: MIPS: SMP: Use a completion event to signal CPU up

From: Matt Redfearn <[email protected]>

commit a00eeede507c975087b7b8df8cf2c9f88ba285de upstream.

If a secondary CPU failed to start, for any reason, the CPU requesting the secondary to start would get stuck in the loop waiting for the secondary to be present in the cpu_callin_map.

Rather than that, use a completion event to signal that the secondary CPU has started and is waiting to synchronise counters.

Since the CPU presence will no longer be marked in cpu_callin_map, remove the redundant test from arch_cpu_idle_dead().

Signed-off-by Matt Redfearn <[email protected]>
Cc Maciej W. Rozycki <[email protected]>
Cc Jiri Slaby <[email protected]>
Cc Paul Gortmaker <[email protected]>
Cc Chris Metcalf <[email protected]>
Cc Thomas Gleixner <[email protected]>
Cc Qais Yousef <[email protected]>
Cc James Hogan <[email protected]>
Cc Paul Burton <[email protected]>
Cc Marcin Nowakowski <[email protected]>
Cc Andrew Morton <[email protected]>
Cc [email protected]
Cc [email protected]

Patchwork: https://patchwork.linux-mips.org/patch/14502/

Signed-off-by Ralf Baechle <[email protected]>
Signed-off-by Greg Kroah-Hartman <[email protected]>
---
 arch/mips/kernel/process.c |    4 +---
 arch/mips/kernel/smp.c     |   15 +++++++++------
 2 files changed, 10 insertions(+), 9 deletions(-)
arch/mips/kernel/process.c +1 -3
@@ -50,9 +50,7 @@
 #ifdef CONFIG_HOTPLUG_CPU
 void arch_cpu_idle_dead(void)
 {
-	/* What the heck is this check doing ? */
-	if (!cpumask_test_cpu(smp_processor_id(), &cpu_callin_map))
-		play_dead();
+	play_dead();
 }
 #endif
arch/mips/kernel/smp.c +9 -6
@@ -68,6 +68,8 @@ EXPORT_SYMBOL(cpu_sibling_map);
 cpumask_t cpu_core_map[NR_CPUS] __read_mostly;
 EXPORT_SYMBOL(cpu_core_map);
 
+static DECLARE_COMPLETION(cpu_running);
+
 /*
  * A logcal cpu mask containing only one VPE per core to
  * reduce the number of IPIs on large MT systems.

@@ -369,7 +371,7 @@ asmlinkage void start_secondary(void)
 	cpumask_set_cpu(cpu, &cpu_coherent_mask);
 	notify_cpu_starting(cpu);
 
-	cpumask_set_cpu(cpu, &cpu_callin_map);
+	complete(&cpu_running);
 	synchronise_count_slave(cpu);
 
 	set_cpu_online(cpu, true);

@@ -430,7 +432,6 @@ void smp_prepare_boot_cpu(void)
 {
 	set_cpu_possible(0, true);
 	set_cpu_online(0, true);
-	cpumask_set_cpu(0, &cpu_callin_map);
 }
 
 int __cpu_up(unsigned int cpu, struct task_struct *tidle)

@@ -438,11 +439,13 @@ int __cpu_up(unsigned int cpu, struct ta
 	mp_ops->boot_secondary(cpu, tidle);
 
 	/*
-	 * Trust is futile.  We should really have timeouts ...
+	 * We must check for timeout here, as the CPU will not be marked
+	 * online until the counters are synchronised.
 	 */
-	while (!cpumask_test_cpu(cpu, &cpu_callin_map)) {
-		udelay(100);
-		schedule();
+	if (!wait_for_completion_timeout(&cpu_running,
+					 msecs_to_jiffies(1000))) {
+		pr_crit("CPU%u: failed to start\n", cpu);
+		return -EIO;
 	}
 
 	synchronise_count_master(cpu);

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/mips-smp-fix-deadlock-online-race.patch queue-4.9/mips-smp-use-a-completion-event-to-signal-cpu-up.patch