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authorLinus Torvalds <torvalds@macmini.osdl.org>2006-07-23 12:12:16 -0700
committerLinus Torvalds <torvalds@macmini.osdl.org>2006-07-23 12:12:16 -0700
commitaa95387774039096c11803c04011f1aa42d85758 (patch)
treeb8d3c845efedc2d67bcaff0038b4306fa375379c /kernel/cpu.c
parent2cd7cbdf4bd0d0fe58e4dc903e8b413412595504 (diff)
downloadlwn-aa95387774039096c11803c04011f1aa42d85758.tar.gz
lwn-aa95387774039096c11803c04011f1aa42d85758.zip
cpu hotplug: simplify and hopefully fix locking
The CPU hotplug locking was quite messy, with a recursive lock to handle the fact that both the actual up/down sequence wanted to protect itself from being re-entered, but the callbacks that it called also tended to want to protect themselves from CPU events. This splits the lock into two (one to serialize the whole hotplug sequence, the other to protect against the CPU present bitmaps changing). The latter still allows recursive usage because some subsystems (ondemand policy for cpufreq at least) had already gotten too used to the lax locking, but the locking mistakes are hopefully now less fundamental, and we now warn about recursive lock usage when we see it, in the hope that it can be fixed. Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'kernel/cpu.c')
-rw-r--r--kernel/cpu.c75
1 files changed, 34 insertions, 41 deletions
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 70fbf2e83766..f230f9ae01c2 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -16,56 +16,48 @@
#include <linux/mutex.h>
/* This protects CPUs going up and down... */
-static DEFINE_MUTEX(cpucontrol);
+static DEFINE_MUTEX(cpu_add_remove_lock);
+static DEFINE_MUTEX(cpu_bitmask_lock);
static __cpuinitdata BLOCKING_NOTIFIER_HEAD(cpu_chain);
#ifdef CONFIG_HOTPLUG_CPU
-static struct task_struct *lock_cpu_hotplug_owner;
-static int lock_cpu_hotplug_depth;
-static int __lock_cpu_hotplug(int interruptible)
-{
- int ret = 0;
-
- if (lock_cpu_hotplug_owner != current) {
- if (interruptible)
- ret = mutex_lock_interruptible(&cpucontrol);
- else
- mutex_lock(&cpucontrol);
- }
-
- /*
- * Set only if we succeed in locking
- */
- if (!ret) {
- lock_cpu_hotplug_depth++;
- lock_cpu_hotplug_owner = current;
- }
-
- return ret;
-}
+/* Crappy recursive lock-takers in cpufreq! Complain loudly about idiots */
+static struct task_struct *recursive;
+static int recursive_depth;
void lock_cpu_hotplug(void)
{
- __lock_cpu_hotplug(0);
+ struct task_struct *tsk = current;
+
+ if (tsk == recursive) {
+ static int warnings = 10;
+ if (warnings) {
+ printk(KERN_ERR "Lukewarm IQ detected in hotplug locking\n");
+ WARN_ON(1);
+ warnings--;
+ }
+ recursive_depth++;
+ return;
+ }
+ mutex_lock(&cpu_bitmask_lock);
+ recursive = tsk;
}
EXPORT_SYMBOL_GPL(lock_cpu_hotplug);
void unlock_cpu_hotplug(void)
{
- if (--lock_cpu_hotplug_depth == 0) {
- lock_cpu_hotplug_owner = NULL;
- mutex_unlock(&cpucontrol);
+ WARN_ON(recursive != current);
+ if (recursive_depth) {
+ recursive_depth--;
+ return;
}
+ mutex_unlock(&cpu_bitmask_lock);
+ recursive = NULL;
}
EXPORT_SYMBOL_GPL(unlock_cpu_hotplug);
-int lock_cpu_hotplug_interruptible(void)
-{
- return __lock_cpu_hotplug(1);
-}
-EXPORT_SYMBOL_GPL(lock_cpu_hotplug_interruptible);
#endif /* CONFIG_HOTPLUG_CPU */
/* Need to know about CPUs going up/down? */
@@ -122,9 +114,7 @@ int cpu_down(unsigned int cpu)
struct task_struct *p;
cpumask_t old_allowed, tmp;
- if ((err = lock_cpu_hotplug_interruptible()) != 0)
- return err;
-
+ mutex_lock(&cpu_add_remove_lock);
if (num_online_cpus() == 1) {
err = -EBUSY;
goto out;
@@ -150,7 +140,10 @@ int cpu_down(unsigned int cpu)
cpu_clear(cpu, tmp);
set_cpus_allowed(current, tmp);
+ mutex_lock(&cpu_bitmask_lock);
p = __stop_machine_run(take_cpu_down, NULL, cpu);
+ mutex_unlock(&cpu_bitmask_lock);
+
if (IS_ERR(p)) {
/* CPU didn't die: tell everyone. Can't complain. */
if (blocking_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED,
@@ -187,7 +180,7 @@ out_thread:
out_allowed:
set_cpus_allowed(current, old_allowed);
out:
- unlock_cpu_hotplug();
+ mutex_unlock(&cpu_add_remove_lock);
return err;
}
#endif /*CONFIG_HOTPLUG_CPU*/
@@ -197,9 +190,7 @@ int __devinit cpu_up(unsigned int cpu)
int ret;
void *hcpu = (void *)(long)cpu;
- if ((ret = lock_cpu_hotplug_interruptible()) != 0)
- return ret;
-
+ mutex_lock(&cpu_add_remove_lock);
if (cpu_online(cpu) || !cpu_present(cpu)) {
ret = -EINVAL;
goto out;
@@ -214,7 +205,9 @@ int __devinit cpu_up(unsigned int cpu)
}
/* Arch-specific enabling code. */
+ mutex_lock(&cpu_bitmask_lock);
ret = __cpu_up(cpu);
+ mutex_unlock(&cpu_bitmask_lock);
if (ret != 0)
goto out_notify;
BUG_ON(!cpu_online(cpu));
@@ -227,6 +220,6 @@ out_notify:
blocking_notifier_call_chain(&cpu_chain,
CPU_UP_CANCELED, hcpu);
out:
- unlock_cpu_hotplug();
+ mutex_unlock(&cpu_add_remove_lock);
return ret;
}