linux-kernel - [ 076/187] acpi_pad: fix power

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Message-Id: <20120712191529.458486531@linuxfoundation.org>
Date:	Thu, 12 Jul 2012 15:33:52 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	Greg KH <gregkh@...uxfoundation.org>,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Stuart Hayes <Stuart_Hayes@...l.com>,
	Len Brown <len.brown@...el.com>
Subject: [ 076/187] acpi_pad: fix power_saving thread deadlock

From: Greg KH <gregkh@...uxfoundation.org>

3.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Stuart Hayes <Stuart_Hayes@...l.com>

commit 5f1601261050251a5ca293378b492a69d590dacb upstream.

The acpi_pad driver can get stuck in destroy_power_saving_task()
waiting for kthread_stop() to stop a power_saving thread.  The problem
is that the isolated_cpus_lock mutex is owned when
destroy_power_saving_task() calls kthread_stop(), which waits for a
power_saving thread to end, and the power_saving thread tries to
acquire the isolated_cpus_lock when it calls round_robin_cpu().  This
patch fixes the issue by making round_robin_cpu() use its own mutex.

https://bugzilla.kernel.org/show_bug.cgi?id=42981

Signed-off-by: Stuart Hayes <Stuart_Hayes@...l.com>
Signed-off-by: Len Brown <len.brown@...el.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/acpi/acpi_pad.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

--- a/drivers/acpi/acpi_pad.c
+++ b/drivers/acpi/acpi_pad.c
@@ -36,6 +36,7 @@
 #define ACPI_PROCESSOR_AGGREGATOR_DEVICE_NAME "Processor Aggregator"
 #define ACPI_PROCESSOR_AGGREGATOR_NOTIFY 0x80
 static DEFINE_MUTEX(isolated_cpus_lock);
+static DEFINE_MUTEX(round_robin_lock);
 
 static unsigned long power_saving_mwait_eax;
 
@@ -107,7 +108,7 @@ static void round_robin_cpu(unsigned int
 	if (!alloc_cpumask_var(&tmp, GFP_KERNEL))
 		return;
 
-	mutex_lock(&isolated_cpus_lock);
+	mutex_lock(&round_robin_lock);
 	cpumask_clear(tmp);
 	for_each_cpu(cpu, pad_busy_cpus)
 		cpumask_or(tmp, tmp, topology_thread_cpumask(cpu));
@@ -116,7 +117,7 @@ static void round_robin_cpu(unsigned int
 	if (cpumask_empty(tmp))
 		cpumask_andnot(tmp, cpu_online_mask, pad_busy_cpus);
 	if (cpumask_empty(tmp)) {
-		mutex_unlock(&isolated_cpus_lock);
+		mutex_unlock(&round_robin_lock);
 		return;
 	}
 	for_each_cpu(cpu, tmp) {
@@ -131,7 +132,7 @@ static void round_robin_cpu(unsigned int
 	tsk_in_cpu[tsk_index] = preferred_cpu;
 	cpumask_set_cpu(preferred_cpu, pad_busy_cpus);
 	cpu_weight[preferred_cpu]++;
-	mutex_unlock(&isolated_cpus_lock);
+	mutex_unlock(&round_robin_lock);
 
 	set_cpus_allowed_ptr(current, cpumask_of(preferred_cpu));
 }


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