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authorThomas Gleixner <tglx@linutronix.de>2009-08-28 20:25:24 +0200
committerThomas Gleixner <tglx@linutronix.de>2009-08-28 20:25:24 +0200
commit7285dd7fd375763bfb8ab1ac9cf3f1206f503c16 (patch)
tree42f809ab3616cc3d93d655acccfc2d54e9f6d0e4
parent90cba64a5f672a239f43ec5cb9a11b806887331e (diff)
downloadop-kernel-dev-7285dd7fd375763bfb8ab1ac9cf3f1206f503c16.zip
op-kernel-dev-7285dd7fd375763bfb8ab1ac9cf3f1206f503c16.tar.gz
clocksource: Resolve cpu hotplug dead lock with TSC unstable
Martin Schwidefsky analyzed it: To register a clocksource the clocksource_mutex is acquired and if necessary timekeeping_notify is called to install the clocksource as the timekeeper clock. timekeeping_notify uses stop_machine which needs to take cpu_add_remove_lock mutex. Starting a new cpu is done with the cpu_add_remove_lock mutex held. native_cpu_up checks the tsc of the new cpu and if the tsc is no good clocksource_change_rating is called. Which needs the clocksource_mutex and the deadlock is complete. The solution is to replace the TSC via the clocksource watchdog mechanism. Mark the TSC as unstable and schedule the watchdog work so it gets removed in the watchdog thread context. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> LKML-Reference: <new-submission> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: John Stultz <johnstul@us.ibm.com>
-rw-r--r--arch/x86/kernel/tsc.c8
-rw-r--r--include/linux/clocksource.h1
-rw-r--r--kernel/time/clocksource.c33
3 files changed, 36 insertions, 6 deletions
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 9684254..fc3672a 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -767,12 +767,14 @@ void mark_tsc_unstable(char *reason)
{
if (!tsc_unstable) {
tsc_unstable = 1;
- printk("Marking TSC unstable due to %s\n", reason);
+ printk(KERN_INFO "Marking TSC unstable due to %s\n", reason);
/* Change only the rating, when not registered */
if (clocksource_tsc.mult)
- clocksource_change_rating(&clocksource_tsc, 0);
- else
+ clocksource_mark_unstable(&clocksource_tsc);
+ else {
+ clocksource_tsc.flags |= CLOCK_SOURCE_UNSTABLE;
clocksource_tsc.rating = 0;
+ }
}
}
diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h
index 9ea40ff..83d2fbd 100644
--- a/include/linux/clocksource.h
+++ b/include/linux/clocksource.h
@@ -277,6 +277,7 @@ extern struct clocksource* clocksource_get_next(void);
extern void clocksource_change_rating(struct clocksource *cs, int rating);
extern void clocksource_resume(void);
extern struct clocksource * __init __weak clocksource_default_clock(void);
+extern void clocksource_mark_unstable(struct clocksource *cs);
#ifdef CONFIG_GENERIC_TIME_VSYSCALL
extern void update_vsyscall(struct timespec *ts, struct clocksource *c);
diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index e0c86ad..a0af4ff 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -149,15 +149,42 @@ static void clocksource_watchdog_work(struct work_struct *work)
kthread_run(clocksource_watchdog_kthread, NULL, "kwatchdog");
}
-static void clocksource_unstable(struct clocksource *cs, int64_t delta)
+static void __clocksource_unstable(struct clocksource *cs)
{
- printk(KERN_WARNING "Clocksource %s unstable (delta = %Ld ns)\n",
- cs->name, delta);
cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
cs->flags |= CLOCK_SOURCE_UNSTABLE;
schedule_work(&watchdog_work);
}
+static void clocksource_unstable(struct clocksource *cs, int64_t delta)
+{
+ printk(KERN_WARNING "Clocksource %s unstable (delta = %Ld ns)\n",
+ cs->name, delta);
+ __clocksource_unstable(cs);
+}
+
+/**
+ * clocksource_mark_unstable - mark clocksource unstable via watchdog
+ * @cs: clocksource to be marked unstable
+ *
+ * This function is called instead of clocksource_change_rating from
+ * cpu hotplug code to avoid a deadlock between the clocksource mutex
+ * and the cpu hotplug mutex. It defers the update of the clocksource
+ * to the watchdog thread.
+ */
+void clocksource_mark_unstable(struct clocksource *cs)
+{
+ unsigned long flags;
+
+ spin_lock_irqsave(&watchdog_lock, flags);
+ if (!(cs->flags & CLOCK_SOURCE_UNSTABLE)) {
+ if (list_empty(&cs->wd_list))
+ list_add(&cs->wd_list, &watchdog_list);
+ __clocksource_unstable(cs);
+ }
+ spin_unlock_irqrestore(&watchdog_lock, flags);
+}
+
static void clocksource_watchdog(unsigned long data)
{
struct clocksource *cs;
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