From a63fbed776c7124ce9f606234267c3c095b2680e Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Wed, 24 May 2017 10:15:34 +0200 Subject: [PATCH] perf/tracing/cpuhotplug: Fix locking order perf, tracing, kprobes and jump_labels have a gazillion of ways to create dependency lock chains. Some of those involve nested invocations of get_online_cpus(). The conversion of the hotplug locking to a percpu rwsem requires to avoid such nested calls. sys_perf_event_open() protects most of the syscall logic against cpu hotplug. This causes nested calls and lock inversions versus ftrace and kprobes in various interesting ways. It's impossible to move the hotplug locking to the outer end of all call chains in the involved facilities, so the hotplug protection in sys_perf_event_open() needs to be solved differently. Introduce 'pmus_mutex' which protects a perf private online cpumask. This mutex is taken when the mask is updated in the cpu hotplug callbacks and can be taken in sys_perf_event_open() to protect the swhash setup/teardown code and when the final judgement about a valid event has to be made. [ tglx: Produced changelog and fixed the swhash interaction ] Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Thomas Gleixner Acked-by: Ingo Molnar Cc: Paul E. McKenney Cc: Sebastian Siewior Cc: Steven Rostedt Cc: Mathieu Desnoyers Cc: Masami Hiramatsu Link: http://lkml.kernel.org/r/20170524081548.930941109@linutronix.de --- include/linux/perf_event.h | 2 + kernel/events/core.c | 106 ++++++++++++++++++++++++++----------- 2 files changed, 78 insertions(+), 30 deletions(-) diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h index 24a635887f28..7d6aa29094b2 100644 --- a/include/linux/perf_event.h +++ b/include/linux/perf_event.h @@ -801,6 +801,8 @@ struct perf_cpu_context { struct list_head sched_cb_entry; int sched_cb_usage; + + int online; }; struct perf_output_handle { diff --git a/kernel/events/core.c b/kernel/events/core.c index 6e75a5c9412d..b97cda4d1777 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -389,6 +389,7 @@ static atomic_t nr_switch_events __read_mostly; static LIST_HEAD(pmus); static DEFINE_MUTEX(pmus_lock); static struct srcu_struct pmus_srcu; +static cpumask_var_t perf_online_mask; /* * perf event paranoia level: @@ -3812,14 +3813,6 @@ find_get_context(struct pmu *pmu, struct task_struct *task, if (perf_paranoid_cpu() && !capable(CAP_SYS_ADMIN)) return ERR_PTR(-EACCES); - /* - * We could be clever and allow to attach a event to an - * offline CPU and activate it when the CPU comes up, but - * that's for later. - */ - if (!cpu_online(cpu)) - return ERR_PTR(-ENODEV); - cpuctx = per_cpu_ptr(pmu->pmu_cpu_context, cpu); ctx = &cpuctx->ctx; get_ctx(ctx); @@ -7703,7 +7696,8 @@ static int swevent_hlist_get_cpu(int cpu) int err = 0; mutex_lock(&swhash->hlist_mutex); - if (!swevent_hlist_deref(swhash) && cpu_online(cpu)) { + if (!swevent_hlist_deref(swhash) && + cpumask_test_cpu(cpu, perf_online_mask)) { struct swevent_hlist *hlist; hlist = kzalloc(sizeof(*hlist), GFP_KERNEL); @@ -7724,7 +7718,7 @@ static int swevent_hlist_get(void) { int err, cpu, failed_cpu; - get_online_cpus(); + mutex_lock(&pmus_lock); for_each_possible_cpu(cpu) { err = swevent_hlist_get_cpu(cpu); if (err) { @@ -7732,8 +7726,7 @@ static int swevent_hlist_get(void) goto fail; } } - put_online_cpus(); - + mutex_unlock(&pmus_lock); return 0; fail: for_each_possible_cpu(cpu) { @@ -7741,8 +7734,7 @@ fail: break; swevent_hlist_put_cpu(cpu); } - - put_online_cpus(); + mutex_unlock(&pmus_lock); return err; } @@ -8920,7 +8912,7 @@ perf_event_mux_interval_ms_store(struct device *dev, pmu->hrtimer_interval_ms = timer; /* update all cpuctx for this PMU */ - get_online_cpus(); + cpus_read_lock(); for_each_online_cpu(cpu) { struct perf_cpu_context *cpuctx; cpuctx = per_cpu_ptr(pmu->pmu_cpu_context, cpu); @@ -8929,7 +8921,7 @@ perf_event_mux_interval_ms_store(struct device *dev, cpu_function_call(cpu, (remote_function_f)perf_mux_hrtimer_restart, cpuctx); } - put_online_cpus(); + cpus_read_unlock(); mutex_unlock(&mux_interval_mutex); return count; @@ -9059,6 +9051,7 @@ skip_type: lockdep_set_class(&cpuctx->ctx.mutex, &cpuctx_mutex); lockdep_set_class(&cpuctx->ctx.lock, &cpuctx_lock); cpuctx->ctx.pmu = pmu; + cpuctx->online = cpumask_test_cpu(cpu, perf_online_mask); __perf_mux_hrtimer_init(cpuctx, cpu); } @@ -9882,12 +9875,10 @@ SYSCALL_DEFINE5(perf_event_open, goto err_task; } - get_online_cpus(); - if (task) { err = mutex_lock_interruptible(&task->signal->cred_guard_mutex); if (err) - goto err_cpus; + goto err_cred; /* * Reuse ptrace permission checks for now. @@ -10073,6 +10064,23 @@ SYSCALL_DEFINE5(perf_event_open, goto err_locked; } + if (!task) { + /* + * Check if the @cpu we're creating an event for is online. + * + * We use the perf_cpu_context::ctx::mutex to serialize against + * the hotplug notifiers. See perf_event_{init,exit}_cpu(). + */ + struct perf_cpu_context *cpuctx = + container_of(ctx, struct perf_cpu_context, ctx); + + if (!cpuctx->online) { + err = -ENODEV; + goto err_locked; + } + } + + /* * Must be under the same ctx::mutex as perf_install_in_context(), * because we need to serialize with concurrent event creation. @@ -10162,8 +10170,6 @@ SYSCALL_DEFINE5(perf_event_open, put_task_struct(task); } - put_online_cpus(); - mutex_lock(¤t->perf_event_mutex); list_add_tail(&event->owner_entry, ¤t->perf_event_list); mutex_unlock(¤t->perf_event_mutex); @@ -10197,8 +10203,6 @@ err_alloc: err_cred: if (task) mutex_unlock(&task->signal->cred_guard_mutex); -err_cpus: - put_online_cpus(); err_task: if (task) put_task_struct(task); @@ -10253,6 +10257,21 @@ perf_event_create_kernel_counter(struct perf_event_attr *attr, int cpu, goto err_unlock; } + if (!task) { + /* + * Check if the @cpu we're creating an event for is online. + * + * We use the perf_cpu_context::ctx::mutex to serialize against + * the hotplug notifiers. See perf_event_{init,exit}_cpu(). + */ + struct perf_cpu_context *cpuctx = + container_of(ctx, struct perf_cpu_context, ctx); + if (!cpuctx->online) { + err = -ENODEV; + goto err_unlock; + } + } + if (!exclusive_event_installable(event, ctx)) { err = -EBUSY; goto err_unlock; @@ -10920,6 +10939,8 @@ static void __init perf_event_init_all_cpus(void) struct swevent_htable *swhash; int cpu; + zalloc_cpumask_var(&perf_online_mask, GFP_KERNEL); + for_each_possible_cpu(cpu) { swhash = &per_cpu(swevent_htable, cpu); mutex_init(&swhash->hlist_mutex); @@ -10935,7 +10956,7 @@ static void __init perf_event_init_all_cpus(void) } } -int perf_event_init_cpu(unsigned int cpu) +void perf_swevent_init_cpu(unsigned int cpu) { struct swevent_htable *swhash = &per_cpu(swevent_htable, cpu); @@ -10948,7 +10969,6 @@ int perf_event_init_cpu(unsigned int cpu) rcu_assign_pointer(swhash->swevent_hlist, hlist); } mutex_unlock(&swhash->hlist_mutex); - return 0; } #if defined CONFIG_HOTPLUG_CPU || defined CONFIG_KEXEC_CORE @@ -10966,19 +10986,22 @@ static void __perf_event_exit_context(void *__info) static void perf_event_exit_cpu_context(int cpu) { + struct perf_cpu_context *cpuctx; struct perf_event_context *ctx; struct pmu *pmu; - int idx; - idx = srcu_read_lock(&pmus_srcu); - list_for_each_entry_rcu(pmu, &pmus, entry) { - ctx = &per_cpu_ptr(pmu->pmu_cpu_context, cpu)->ctx; + mutex_lock(&pmus_lock); + list_for_each_entry(pmu, &pmus, entry) { + cpuctx = per_cpu_ptr(pmu->pmu_cpu_context, cpu); + ctx = &cpuctx->ctx; mutex_lock(&ctx->mutex); smp_call_function_single(cpu, __perf_event_exit_context, ctx, 1); + cpuctx->online = 0; mutex_unlock(&ctx->mutex); } - srcu_read_unlock(&pmus_srcu, idx); + cpumask_clear_cpu(cpu, perf_online_mask); + mutex_unlock(&pmus_lock); } #else @@ -10986,6 +11009,29 @@ static void perf_event_exit_cpu_context(int cpu) { } #endif +int perf_event_init_cpu(unsigned int cpu) +{ + struct perf_cpu_context *cpuctx; + struct perf_event_context *ctx; + struct pmu *pmu; + + perf_swevent_init_cpu(cpu); + + mutex_lock(&pmus_lock); + cpumask_set_cpu(cpu, perf_online_mask); + list_for_each_entry(pmu, &pmus, entry) { + cpuctx = per_cpu_ptr(pmu->pmu_cpu_context, cpu); + ctx = &cpuctx->ctx; + + mutex_lock(&ctx->mutex); + cpuctx->online = 1; + mutex_unlock(&ctx->mutex); + } + mutex_unlock(&pmus_lock); + + return 0; +} + int perf_event_exit_cpu(unsigned int cpu) { perf_event_exit_cpu_context(cpu);