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tick: broadcast: Prevent livelock from event handler 

With the removal of the hrtimer softirq the switch to highres/nohz
mode happens in the tick interrupt. That leads to a livelock when the
per cpu event handler is directly called from the broadcast handler
under broadcast lock because broadcast lock needs to be taken for the
highres/nohz switch as well.

Solve this by calling the cpu local handler outside the broadcast_lock
held region.

Fixes: c6eb3f70d4 "hrtimer: Get rid of hrtimer softirq"
Reported-and-tested-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Thomas Gleixner 2015-05-05 10:00:13 +02:00
parent 30fbd59057
commit 2951d5c031
1 changed files with 26 additions and 29 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

55
kernel/time/tick-broadcast.c
View File

@ -255,18 +255,18 @@ int tick_receive_broadcast(void)
/*
* Broadcast the event to the cpus, which are set in the mask (mangled).
*/
static void tick_do_broadcast(struct cpumask *mask)
static bool tick_do_broadcast(struct cpumask *mask)
{
int cpu = smp_processor_id();
struct tick_device *td;
bool local = false;
/*
* Check, if the current cpu is in the mask
*/
if (cpumask_test_cpu(cpu, mask)) {
cpumask_clear_cpu(cpu, mask);
td = &per_cpu(tick_cpu_device, cpu);
td->evtdev->event_handler(td->evtdev);
local = true;
}
if (!cpumask_empty(mask)) {
@ -279,16 +279,17 @@ static void tick_do_broadcast(struct cpumask *mask)
td = &per_cpu(tick_cpu_device, cpumask_first(mask));
td->evtdev->broadcast(mask);
}
return local;
}
/*
* Periodic broadcast:
* - invoke the broadcast handlers
*/
static void tick_do_periodic_broadcast(void)
static bool tick_do_periodic_broadcast(void)
{
cpumask_and(tmpmask, cpu_online_mask, tick_broadcast_mask);
tick_do_broadcast(tmpmask);
return tick_do_broadcast(tmpmask);
}
/*
@ -296,34 +297,26 @@ static void tick_do_periodic_broadcast(void)
*/
static void tick_handle_periodic_broadcast(struct clock_event_device *dev)
{
ktime_t next;
struct tick_device *td = this_cpu_ptr(&tick_cpu_device);
bool bc_local;
raw_spin_lock(&tick_broadcast_lock);
bc_local = tick_do_periodic_broadcast();
tick_do_periodic_broadcast();
if (dev->state == CLOCK_EVT_STATE_ONESHOT) {
ktime_t next = ktime_add(dev->next_event, tick_period);
/*
* The device is in periodic mode. No reprogramming necessary:
*/
if (dev->state == CLOCK_EVT_STATE_PERIODIC)
goto unlock;
/*
* Setup the next period for devices, which do not have
* periodic mode. We read dev->next_event first and add to it
* when the event already expired. clockevents_program_event()
* sets dev->next_event only when the event is really
* programmed to the device.
*/
for (next = dev->next_event; ;) {
next = ktime_add(next, tick_period);
if (!clockevents_program_event(dev, next, false))
goto unlock;
tick_do_periodic_broadcast();
clockevents_program_event(dev, next, true);
}
unlock:
raw_spin_unlock(&tick_broadcast_lock);
/*
* We run the handler of the local cpu after dropping
* tick_broadcast_lock because the handler might deadlock when
* trying to switch to oneshot mode.
*/
if (bc_local)
td->evtdev->event_handler(td->evtdev);
}
/**
@ -622,9 +615,13 @@ again:
cpumask_and(tmpmask, tmpmask, cpu_online_mask);
/*
* Wakeup the cpus which have an expired event.
* Wakeup the cpus which have an expired event and handle the
* broadcast event of the local cpu.
*/
tick_do_broadcast(tmpmask);
if (tick_do_broadcast(tmpmask)) {
td = this_cpu_ptr(&tick_cpu_device);
td->evtdev->event_handler(td->evtdev);
}
/*
* Two reasons for reprogram: