From: Heiko Carstens <heiko.carstens@de.ibm.com>
Date: Wed, 30 Apr 2008 11:38:36 +0000 (+0200)
Subject: [S390] smp: Fix locking order.
X-Git-Tag: v2.6.26-rc1~107^2~14
X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=0b18d318b80a7f350648ca8f7cc00a2f688104cb;p=linux-2.6

[S390] smp: Fix locking order.

On some smp sysfs store attributes get_online_cpus() may block on
cpu_hotplug.lock, but we hold already smp_cpu_state_mutex. Since the
locking order on cpu hotplug via arch_update_cpu_topology is inverse
this might lead to deadlocks.
So make sure locking order is always the same.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
---

diff --git a/arch/s390/kernel/smp.c b/arch/s390/kernel/smp.c
index 0dfa988c1b..6bb5c05064 100644
--- a/arch/s390/kernel/smp.c
+++ b/arch/s390/kernel/smp.c
@@ -890,8 +890,8 @@ static ssize_t cpu_configure_store(struct sys_device *dev, const char *buf,
 	if (val != 0 && val != 1)
 		return -EINVAL;
 
-	mutex_lock(&smp_cpu_state_mutex);
 	get_online_cpus();
+	mutex_lock(&smp_cpu_state_mutex);
 	rc = -EBUSY;
 	if (cpu_online(cpu))
 		goto out;
@@ -919,8 +919,8 @@ static ssize_t cpu_configure_store(struct sys_device *dev, const char *buf,
 		break;
 	}
 out:
-	put_online_cpus();
 	mutex_unlock(&smp_cpu_state_mutex);
+	put_online_cpus();
 	return rc ? rc : count;
 }
 static SYSDEV_ATTR(configure, 0644, cpu_configure_show, cpu_configure_store);
@@ -1095,8 +1095,8 @@ static ssize_t __ref rescan_store(struct sys_device *dev,
 	int cpu;
 	int rc;
 
-	mutex_lock(&smp_cpu_state_mutex);
 	get_online_cpus();
+	mutex_lock(&smp_cpu_state_mutex);
 	newcpus = cpu_present_map;
 	rc = smp_rescan_cpus();
 	if (rc)
@@ -1109,8 +1109,8 @@ static ssize_t __ref rescan_store(struct sys_device *dev,
 	}
 	rc = 0;
 out:
-	put_online_cpus();
 	mutex_unlock(&smp_cpu_state_mutex);
+	put_online_cpus();
 	if (!cpus_empty(newcpus))
 		topology_schedule_update();
 	return rc ? rc : count;
@@ -1139,16 +1139,16 @@ static ssize_t dispatching_store(struct sys_device *dev, const char *buf,
 	if (val != 0 && val != 1)
 		return -EINVAL;
 	rc = 0;
-	mutex_lock(&smp_cpu_state_mutex);
 	get_online_cpus();
+	mutex_lock(&smp_cpu_state_mutex);
 	if (cpu_management == val)
 		goto out;
 	rc = topology_set_cpu_management(val);
 	if (!rc)
 		cpu_management = val;
 out:
-	put_online_cpus();
 	mutex_unlock(&smp_cpu_state_mutex);
+	put_online_cpus();
 	return rc ? rc : count;
 }
 static SYSDEV_ATTR(dispatching, 0644, dispatching_show, dispatching_store);