From c7999c6f3fed9e383d3131474588f282ae6d56b9 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Tue, 4 Aug 2015 19:22:49 +0200 Subject: [PATCH] perf: Fix PERF_EVENT_IOC_PERIOD migration race I ran the perf fuzzer, which triggered some WARN()s which are due to trying to stop/restart an event on the wrong CPU. Use the normal IPI pattern to ensure we run the code on the correct CPU. Signed-off-by: Peter Zijlstra (Intel) Cc: Vince Weaver Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Fixes: bad7192b842c ("perf: Fix PERF_EVENT_IOC_PERIOD to force-reset the period") Signed-off-by: Ingo Molnar --- kernel/events/core.c | 75 ++++++++++++++++++++++++++++++++------------ 1 file changed, 55 insertions(+), 20 deletions(-) diff --git a/kernel/events/core.c b/kernel/events/core.c index 072b8a686517..e6feb5114134 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -3958,28 +3958,21 @@ static void perf_event_for_each(struct perf_event *event, perf_event_for_each_child(sibling, func); } -static int perf_event_period(struct perf_event *event, u64 __user *arg) -{ - struct perf_event_context *ctx = event->ctx; - int ret = 0, active; +struct period_event { + struct perf_event *event; u64 value; +}; - if (!is_sampling_event(event)) - return -EINVAL; - - if (copy_from_user(&value, arg, sizeof(value))) - return -EFAULT; - - if (!value) - return -EINVAL; +static int __perf_event_period(void *info) +{ + struct period_event *pe = info; + struct perf_event *event = pe->event; + struct perf_event_context *ctx = event->ctx; + u64 value = pe->value; + bool active; - raw_spin_lock_irq(&ctx->lock); + raw_spin_lock(&ctx->lock); if (event->attr.freq) { - if (value > sysctl_perf_event_sample_rate) { - ret = -EINVAL; - goto unlock; - } - event->attr.sample_freq = value; } else { event->attr.sample_period = value; @@ -3998,11 +3991,53 @@ static int perf_event_period(struct perf_event *event, u64 __user *arg) event->pmu->start(event, PERF_EF_RELOAD); perf_pmu_enable(ctx->pmu); } + raw_spin_unlock(&ctx->lock); -unlock: + return 0; +} + +static int perf_event_period(struct perf_event *event, u64 __user *arg) +{ + struct period_event pe = { .event = event, }; + struct perf_event_context *ctx = event->ctx; + struct task_struct *task; + u64 value; + + if (!is_sampling_event(event)) + return -EINVAL; + + if (copy_from_user(&value, arg, sizeof(value))) + return -EFAULT; + + if (!value) + return -EINVAL; + + if (event->attr.freq && value > sysctl_perf_event_sample_rate) + return -EINVAL; + + task = ctx->task; + pe.value = value; + + if (!task) { + cpu_function_call(event->cpu, __perf_event_period, &pe); + return 0; + } + +retry: + if (!task_function_call(task, __perf_event_period, &pe)) + return 0; + + raw_spin_lock_irq(&ctx->lock); + if (ctx->is_active) { + raw_spin_unlock_irq(&ctx->lock); + task = ctx->task; + goto retry; + } + + __perf_event_period(&pe); raw_spin_unlock_irq(&ctx->lock); - return ret; + return 0; } static const struct file_operations perf_fops; -- 2.20.1