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

[<gregkh@linuxfoundation.org>]

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 <stable@vger.kernel.org> know about it.


>From a00eeede507c975087b7b8df8cf2c9f88ba285de Mon Sep 17 00:00:00 2001
From: Matt Redfearn <matt.redfearn@imgtec.com>
Date: Fri, 4 Nov 2016 09:28:56 +0000
Subject: MIPS: SMP: Use a completion event to signal CPU up

From: Matt Redfearn <matt.redfearn@imgtec.com>

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 <matt.redfearn@imgtec.com>
Cc: Maciej W. Rozycki <macro@imgtec.com>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Qais Yousef <qsyousef@gmail.com>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: Paul Burton <paul.burton@imgtec.com>
Cc: Marcin Nowakowski <marcin.nowakowski@imgtec.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/14502/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/mips/kernel/process.c |    4 +---
 arch/mips/kernel/smp.c     |   15 +++++++++------
 2 files changed, 10 insertions(+), 9 deletions(-)

--- a/arch/mips/kernel/process.c
+++ b/arch/mips/kernel/process.c
@@ -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
 
--- a/arch/mips/kernel/smp.c
+++ b/arch/mips/kernel/smp.c
@@ -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 matt.redfearn@imgtec.com 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