linux-kernel - [PATCH 2/3] stop_machine: add timeout for child thread deployment

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Date:	Tue, 29 Apr 2008 10:31:43 +0900
From:	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
To:	Rusty Russell <rusty@...tcorp.com.au>, linux-kernel@...r.kernel.org
Subject: [PATCH 2/3] stop_machine: add timeout for child thread deployment

If stopmachine() invoked while one of onlined cpu is locked up
by some reason, stopmachine cannot finish its work because the
locked cpu cannot stop.

This patch allows stopmachine to return -EBUSY if any of
kstopmachine's child threads cannot start running on its target
cpu.

Signed-off-by: Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
---
 kernel/stop_machine.c |   40 +++++++++++++++++++++++++++++++++++++++-
 1 files changed, 39 insertions(+), 1 deletions(-)

Index: GIT-torvalds/kernel/stop_machine.c
===================================================================
--- GIT-torvalds.orig/kernel/stop_machine.c	2008-04-29 00:29:20.000000000 +0900
+++ GIT-torvalds/kernel/stop_machine.c	2008-04-29 00:31:55.000000000 +0900
@@ -29,6 +29,9 @@
 static enum stopmachine_state stopmachine_state;
 static unsigned int stopmachine_num_threads;
 static atomic_t stopmachine_thread_ack;
+static atomic_t stopmachine_busy_exit;
+
+static unsigned long stopmachine_timeout = 5; /* secs, arbitrary */
 
 static int stopmachine(void *cpu)
 {
@@ -42,6 +45,7 @@
 	if (stopmachine_state == STOPMACHINE_EXIT)
 		goto exit;
 
+	/* If target cpu is on fire, this call can stuck */
 	set_cpus_allowed_ptr(current, &cpumask_of_cpu((int)(long)cpu));
 
 	/* Ack: we arrived */
@@ -83,6 +87,12 @@
 	if (prepared)
 		preempt_enable();
 
+	if (atomic_read(&stopmachine_busy_exit)) {
+		atomic_dec(&stopmachine_busy_exit);
+		printk(KERN_INFO "stopmachine: cpu#%d is not busy now.\n",
+			(int)(long)cpu);
+	}
+
 	return 0;
 }
 
@@ -99,6 +109,15 @@
 static int stop_machine(void)
 {
 	int i, ret = 0;
+	unsigned long limit;
+
+	if (atomic_read(&stopmachine_busy_exit)) {
+		/*
+		 * previous try was timeout, and still there is a unreachable
+		 * cpu and abandoned child.
+		 */
+		return -EBUSY;
+	}
 
 	atomic_set(&stopmachine_thread_ack, 0);
 	stopmachine_num_threads = 0;
@@ -113,10 +132,15 @@
 		stopmachine_num_threads++;
 	}
 
+	limit = jiffies + msecs_to_jiffies(stopmachine_timeout * MSEC_PER_SEC);
+
 	/* Wait for them all to come to life on the target. */
 	stopmachine_state = STOPMACHINE_DEPLOY;
 	while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads)
-		yield();
+		if (time_is_after_jiffies(limit))
+			yield();
+		else
+			goto deploy_timeout;
 
 	/* Now they are all started, make them hold the CPUs, ready. */
 	preempt_disable();
@@ -129,6 +153,20 @@
 
 	return 0;
 
+deploy_timeout:
+	printk(KERN_CRIT "stopmachine: Failed to stop machine in time(%lds). "
+		"Are there any CPUs on file?\n", stopmachine_timeout);
+
+	/* defer exit check to the beginning of next try. */
+	atomic_set(&stopmachine_busy_exit, stopmachine_num_threads);
+
+	printk(KERN_INFO "stopmachine: cpu#%d is initiator of failed stop.\n",
+			raw_smp_processor_id());
+	smp_wmb();
+	stopmachine_state = STOPMACHINE_EXIT;
+
+	return -EBUSY;
+
 exit_threads:
 	/* Wait for them all to exit, since stop is canceled */
 	stopmachine_set_state(STOPMACHINE_EXIT);
--
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