[PATCH] x86/mce: Make timer handling more robust

[Thomas Gleixner]

Erik reported that on a preproduction hardware a CMCI storm triggers the
BUG_ON in add_timer_on(). The reason is that the per CPU MCE timer is
started by the CMCI logic before the MCE cpu hotplug callback starts the
timer with add_timer_on(). So the timer is already queued which triggers
the BUG.

Using add_timer_on() is pretty pointless in this code because the timer is
strictlty per CPU, initialized as pinned and all operations which arm the
timer happen on the CPU to which the timer belongs.

Simplify the whole machinery by using mod_timer() instead of add_timer_on()
which avoids the problem because mod_timer() can handle already queued
timers. Use __start_timer() everywhere so the earliest armed expiry time is
preserved.

Reported-by: Erik Veijola <erik.veijola@xxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Tony Luck <tony.luck@xxxxxxxxx>
---
 arch/x86/kernel/cpu/mcheck/mce.c |   31 ++++++++++++-------------------
 1 file changed, 12 insertions(+), 19 deletions(-)

--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -1373,20 +1373,15 @@ static unsigned long mce_adjust_timer_de
 
 static unsigned long (*mce_adjust_timer)(unsigned long interval) = mce_adjust_timer_default;
 
-static void __restart_timer(struct timer_list *t, unsigned long interval)
+static void __start_timer(struct timer_list *t, unsigned long interval)
 {
 	unsigned long when = jiffies + interval;
 	unsigned long flags;
 
 	local_irq_save(flags);
 
-	if (timer_pending(t)) {
-		if (time_before(when, t->expires))
-			mod_timer(t, when);
-	} else {
-		t->expires = round_jiffies(when);
-		add_timer_on(t, smp_processor_id());
-	}
+	if (!timer_pending(t) || time_before(when, t->expires))
+		mod_timer(t, round_jiffies(when));
 
 	local_irq_restore(flags);
 }
@@ -1421,7 +1416,7 @@ static void mce_timer_fn(unsigned long d
 
 done:
 	__this_cpu_write(mce_next_interval, iv);
-	__restart_timer(t, iv);
+	__start_timer(t, iv);
 }
 
 /*
@@ -1432,7 +1427,7 @@ void mce_timer_kick(unsigned long interv
 	struct timer_list *t = this_cpu_ptr(&mce_timer);
 	unsigned long iv = __this_cpu_read(mce_next_interval);
 
-	__restart_timer(t, interval);
+	__start_timer(t, interval);
 
 	if (interval < iv)
 		__this_cpu_write(mce_next_interval, interval);
@@ -1779,17 +1774,15 @@ static void __mcheck_cpu_clear_vendor(st
 	}
 }
 
-static void mce_start_timer(unsigned int cpu, struct timer_list *t)
+static void mce_start_timer(struct timer_list *t)
 {
 	unsigned long iv = check_interval * HZ;
 
 	if (mca_cfg.ignore_ce || !iv)
 		return;
 
-	per_cpu(mce_next_interval, cpu) = iv;
-
-	t->expires = round_jiffies(jiffies + iv);
-	add_timer_on(t, cpu);
+	this_cpu_write(mce_next_interval, iv);
+	__start_timer(t, jiffies + iv);
 }
 
 static void __mcheck_cpu_setup_timer(void)
@@ -1806,7 +1799,7 @@ static void __mcheck_cpu_init_timer(void
 	unsigned int cpu = smp_processor_id();
 
 	setup_pinned_timer(t, mce_timer_fn, cpu);
-	mce_start_timer(cpu, t);
+	mce_start_timer(t);
 }
 
 /* Handle unconfigured int18 (should never happen) */
@@ -2566,7 +2559,7 @@ static int mce_cpu_dead(unsigned int cpu
 
 static int mce_cpu_online(unsigned int cpu)
 {
-	struct timer_list *t = &per_cpu(mce_timer, cpu);
+	struct timer_list *t = this_cpu_ptr(&mce_timer);
 	int ret;
 
 	mce_device_create(cpu);
@@ -2577,13 +2570,13 @@ static int mce_cpu_online(unsigned int c
 		return ret;
 	}
 	mce_reenable_cpu();
-	mce_start_timer(cpu, t);
+	mce_start_timer(t);
 	return 0;
 }
 
 static int mce_cpu_pre_down(unsigned int cpu)
 {
-	struct timer_list *t = &per_cpu(mce_timer, cpu);
+	struct timer_list *t = this_cpu_ptr(&mce_timer);
 
 	mce_disable_cpu();
 	del_timer_sync(t);