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perf: Fix mux_interval hrtimer wreckage
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Thomas stumbled over the hrtimer_forward_now() in
perf_event_mux_interval_ms_store() and noticed its broken-ness.

You cannot just change the expiry time of an active timer, it will
destroy the red-black tree order and cause havoc.

Change it to (re)start the timer instead, (re)starting a timer will
dequeue and enqueue a timer and therefore preserve rb-tree order.

Since we cannot enqueue remotely, wrap the thing in
cpu_function_call(), this however mandates that we restrict ourselves
to online cpus. Also serialize the entire setting so we don't get
multiple concurrent threads trying to update to different values.

Also fix a problem in perf_mux_hrtimer_restart(), checking against
hrtimer_active() can actually loose us the timer when timer->state ==
HRTIMER_STATE_CALLBACK and the callback has already decided NORESTART.

Furthermore it doesn't make any sense to test
hrtimer_callback_running() when we already tested hrtimer_active(),
but with the above change, we explicitly must call it when
callback_running.

Lastly, rename a few functions:

  s/perf_cpu_hrtimer_/perf_mux_hrtimer_/ -- because I could not find
                                            the mux timer function

  s/\<hr\>/timer/ -- because that's the normal way of calling things.

Fixes: 62b8563 ("perf: Add sysfs entry to adjust multiplexing interval per PMU")
Reported-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20150415095011.863052571@infradead.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Peter Zijlstra authored and Thomas Gleixner committed Apr 22, 2015
1 parent 77a4d1a commit 272325c
Showing 1 changed file with 36 additions and 27 deletions.
63 changes: 36 additions & 27 deletions kernel/events/core.c
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Original file line number Diff line number Diff line change
Expand Up @@ -51,9 +51,11 @@

static struct workqueue_struct *perf_wq;

typedef int (*remote_function_f)(void *);

struct remote_function_call {
struct task_struct *p;
int (*func)(void *info);
remote_function_f func;
void *info;
int ret;
};
Expand Down Expand Up @@ -86,7 +88,7 @@ static void remote_function(void *data)
* -EAGAIN - when the process moved away
*/
static int
task_function_call(struct task_struct *p, int (*func) (void *info), void *info)
task_function_call(struct task_struct *p, remote_function_f func, void *info)
{
struct remote_function_call data = {
.p = p,
Expand All @@ -110,7 +112,7 @@ task_function_call(struct task_struct *p, int (*func) (void *info), void *info)
*
* returns: @func return value or -ENXIO when the cpu is offline
*/
static int cpu_function_call(int cpu, int (*func) (void *info), void *info)
static int cpu_function_call(int cpu, remote_function_f func, void *info)
{
struct remote_function_call data = {
.p = NULL,
Expand Down Expand Up @@ -747,7 +749,7 @@ perf_cgroup_mark_enabled(struct perf_event *event,
/*
* function must be called with interrupts disbled
*/
static enum hrtimer_restart perf_cpu_hrtimer_handler(struct hrtimer *hr)
static enum hrtimer_restart perf_mux_hrtimer_handler(struct hrtimer *hr)
{
struct perf_cpu_context *cpuctx;
enum hrtimer_restart ret = HRTIMER_NORESTART;
Expand All @@ -771,7 +773,7 @@ static enum hrtimer_restart perf_cpu_hrtimer_handler(struct hrtimer *hr)
}

/* CPU is going down */
void perf_cpu_hrtimer_cancel(int cpu)
void perf_mux_hrtimer_cancel(int cpu)
{
struct perf_cpu_context *cpuctx;
struct pmu *pmu;
Expand All @@ -798,11 +800,11 @@ void perf_cpu_hrtimer_cancel(int cpu)
local_irq_restore(flags);
}

static void __perf_cpu_hrtimer_init(struct perf_cpu_context *cpuctx, int cpu)
static void __perf_mux_hrtimer_init(struct perf_cpu_context *cpuctx, int cpu)
{
struct hrtimer *hr = &cpuctx->hrtimer;
struct hrtimer *timer = &cpuctx->hrtimer;
struct pmu *pmu = cpuctx->ctx.pmu;
int timer;
u64 interval;

/* no multiplexing needed for SW PMU */
if (pmu->task_ctx_nr == perf_sw_context)
Expand All @@ -812,29 +814,30 @@ static void __perf_cpu_hrtimer_init(struct perf_cpu_context *cpuctx, int cpu)
* check default is sane, if not set then force to
* default interval (1/tick)
*/
timer = pmu->hrtimer_interval_ms;
if (timer < 1)
timer = pmu->hrtimer_interval_ms = PERF_CPU_HRTIMER;
interval = pmu->hrtimer_interval_ms;
if (interval < 1)
interval = pmu->hrtimer_interval_ms = PERF_CPU_HRTIMER;

cpuctx->hrtimer_interval = ns_to_ktime(NSEC_PER_MSEC * timer);
cpuctx->hrtimer_interval = ns_to_ktime(NSEC_PER_MSEC * interval);

hrtimer_init(hr, CLOCK_MONOTONIC, HRTIMER_MODE_REL_PINNED);
hr->function = perf_cpu_hrtimer_handler;
hrtimer_init(timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_PINNED);
timer->function = perf_mux_hrtimer_handler;
}

static void perf_cpu_hrtimer_restart(struct perf_cpu_context *cpuctx)
static int perf_mux_hrtimer_restart(struct perf_cpu_context *cpuctx)
{
struct hrtimer *hr = &cpuctx->hrtimer;
struct hrtimer *timer = &cpuctx->hrtimer;
struct pmu *pmu = cpuctx->ctx.pmu;

/* not for SW PMU */
if (pmu->task_ctx_nr == perf_sw_context)
return;
return 0;

if (hrtimer_active(hr))
return;
if (hrtimer_is_queued(timer))
return 0;

hrtimer_start(hr, cpuctx->hrtimer_interval, HRTIMER_MODE_REL_PINNED);
hrtimer_start(timer, cpuctx->hrtimer_interval, HRTIMER_MODE_REL_PINNED);
return 0;
}

void perf_pmu_disable(struct pmu *pmu)
Expand Down Expand Up @@ -1913,7 +1916,7 @@ group_sched_in(struct perf_event *group_event,

if (event_sched_in(group_event, cpuctx, ctx)) {
pmu->cancel_txn(pmu);
perf_cpu_hrtimer_restart(cpuctx);
perf_mux_hrtimer_restart(cpuctx);
return -EAGAIN;
}

Expand Down Expand Up @@ -1960,7 +1963,7 @@ group_sched_in(struct perf_event *group_event,

pmu->cancel_txn(pmu);

perf_cpu_hrtimer_restart(cpuctx);
perf_mux_hrtimer_restart(cpuctx);

return -EAGAIN;
}
Expand Down Expand Up @@ -2233,7 +2236,7 @@ static int __perf_event_enable(void *info)
*/
if (leader != event) {
group_sched_out(leader, cpuctx, ctx);
perf_cpu_hrtimer_restart(cpuctx);
perf_mux_hrtimer_restart(cpuctx);
}
if (leader->attr.pinned) {
update_group_times(leader);
Expand Down Expand Up @@ -7143,6 +7146,8 @@ perf_event_mux_interval_ms_show(struct device *dev,
return snprintf(page, PAGE_SIZE-1, "%d\n", pmu->hrtimer_interval_ms);
}

static DEFINE_MUTEX(mux_interval_mutex);

static ssize_t
perf_event_mux_interval_ms_store(struct device *dev,
struct device_attribute *attr,
Expand All @@ -7162,17 +7167,21 @@ perf_event_mux_interval_ms_store(struct device *dev,
if (timer == pmu->hrtimer_interval_ms)
return count;

mutex_lock(&mux_interval_mutex);
pmu->hrtimer_interval_ms = timer;

/* update all cpuctx for this PMU */
for_each_possible_cpu(cpu) {
get_online_cpus();
for_each_online_cpu(cpu) {
struct perf_cpu_context *cpuctx;
cpuctx = per_cpu_ptr(pmu->pmu_cpu_context, cpu);
cpuctx->hrtimer_interval = ns_to_ktime(NSEC_PER_MSEC * timer);

if (hrtimer_active(&cpuctx->hrtimer))
hrtimer_forward_now(&cpuctx->hrtimer, cpuctx->hrtimer_interval);
cpu_function_call(cpu,
(remote_function_f)perf_mux_hrtimer_restart, cpuctx);
}
put_online_cpus();
mutex_unlock(&mux_interval_mutex);

return count;
}
Expand Down Expand Up @@ -7277,7 +7286,7 @@ int perf_pmu_register(struct pmu *pmu, const char *name, int type)
lockdep_set_class(&cpuctx->ctx.lock, &cpuctx_lock);
cpuctx->ctx.pmu = pmu;

__perf_cpu_hrtimer_init(cpuctx, cpu);
__perf_mux_hrtimer_init(cpuctx, cpu);

cpuctx->unique_pmu = pmu;
}
Expand Down

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