1 files changed, 91 insertions, 20 deletions

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 517d827f4982..671f6c8c8a32 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -31,6 +31,7 @@
 #include <linux/kernel_stat.h>
 #include <linux/perf_event.h>
 #include <linux/ftrace_event.h>
+#include <linux/hw_breakpoint.h>
 
 #include <asm/irq_regs.h>
 
@@ -674,6 +675,8 @@ event_sched_in(struct perf_event *event,
 
         event->tstamp_running += ctx->time - event->tstamp_stopped;
 
+        event->shadow_ctx_time = ctx->time - ctx->timestamp;
+
         if (!is_software_event(event))
                 cpuctx->active_oncpu++;
         ctx->nr_active++;
@@ -2232,11 +2235,6 @@ int perf_event_release_kernel(struct perf_event *event)
         raw_spin_unlock_irq(&ctx->lock);
         mutex_unlock(&ctx->mutex);
 
-        mutex_lock(&event->owner->perf_event_mutex);
-        list_del_init(&event->owner_entry);
-        mutex_unlock(&event->owner->perf_event_mutex);
-        put_task_struct(event->owner);
-
         free_event(event);
 
         return 0;
@@ -2249,9 +2247,43 @@ EXPORT_SYMBOL_GPL(perf_event_release_kernel);
 static int perf_release(struct inode *inode, struct file *file)
 {
         struct perf_event *event = file->private_data;
+        struct task_struct *owner;
 
         file->private_data = NULL;
 
+        rcu_read_lock();
+        owner = ACCESS_ONCE(event->owner);
+        /*
+         * Matches the smp_wmb() in perf_event_exit_task(). If we observe
+         * !owner it means the list deletion is complete and we can indeed
+         * free this event, otherwise we need to serialize on
+         * owner->perf_event_mutex.
+         */
+        smp_read_barrier_depends();
+        if (owner) {
+                /*
+                 * Since delayed_put_task_struct() also drops the last
+                 * task reference we can safely take a new reference
+                 * while holding the rcu_read_lock().
+                 */
+                get_task_struct(owner);
+        }
+        rcu_read_unlock();
+
+        if (owner) {
+                mutex_lock(&owner->perf_event_mutex);
+                /*
+                 * We have to re-check the event->owner field, if it is cleared
+                 * we raced with perf_event_exit_task(), acquiring the mutex
+                 * ensured they're done, and we can proceed with freeing the
+                 * event.
+                 */
+                if (event->owner)
+                        list_del_init(&event->owner_entry);
+                mutex_unlock(&owner->perf_event_mutex);
+                put_task_struct(owner);
+        }
+
         return perf_event_release_kernel(event);
 }
 
@@ -3396,7 +3428,8 @@ static u32 perf_event_tid(struct perf_event *event, struct task_struct *p)
 }
 
 static void perf_output_read_one(struct perf_output_handle *handle,
-                                 struct perf_event *event)
+                                 struct perf_event *event,
+                                 u64 enabled, u64 running)
 {
         u64 read_format = event->attr.read_format;
         u64 values[4];
@@ -3404,11 +3437,11 @@ static void perf_output_read_one(struct perf_output_handle *handle,
 
         values[n++] = perf_event_count(event);
         if (read_format & PERF_FORMAT_TOTAL_TIME_ENABLED) {
-                values[n++] = event->total_time_enabled +
+                values[n++] = enabled +
                         atomic64_read(&event->child_total_time_enabled);
         }
         if (read_format & PERF_FORMAT_TOTAL_TIME_RUNNING) {
-                values[n++] = event->total_time_running +
+                values[n++] = running +
                         atomic64_read(&event->child_total_time_running);
         }
         if (read_format & PERF_FORMAT_ID)
@@ -3421,7 +3454,8 @@ static void perf_output_read_one(struct perf_output_handle *handle,
  * XXX PERF_FORMAT_GROUP vs inherited events seems difficult.
  */
 static void perf_output_read_group(struct perf_output_handle *handle,
-                            struct perf_event *event)
+                            struct perf_event *event,
+                            u64 enabled, u64 running)
 {
         struct perf_event *leader = event->group_leader, *sub;
         u64 read_format = event->attr.read_format;
@@ -3431,10 +3465,10 @@ static void perf_output_read_group(struct perf_output_handle *handle,
         values[n++] = 1 + leader->nr_siblings;
 
         if (read_format & PERF_FORMAT_TOTAL_TIME_ENABLED)
-                values[n++] = leader->total_time_enabled;
+                values[n++] = enabled;
 
         if (read_format & PERF_FORMAT_TOTAL_TIME_RUNNING)
-                values[n++] = leader->total_time_running;
+                values[n++] = running;
 
         if (leader != event)
                 leader->pmu->read(leader);
@@ -3459,13 +3493,35 @@ static void perf_output_read_group(struct perf_output_handle *handle,
         }
 }
 
+#define PERF_FORMAT_TOTAL_TIMES (PERF_FORMAT_TOTAL_TIME_ENABLED|\
+                                 PERF_FORMAT_TOTAL_TIME_RUNNING)
+
 static void perf_output_read(struct perf_output_handle *handle,
                              struct perf_event *event)
 {
+        u64 enabled = 0, running = 0, now, ctx_time;
+        u64 read_format = event->attr.read_format;
+
+        /*
+         * compute total_time_enabled, total_time_running
+         * based on snapshot values taken when the event
+         * was last scheduled in.
+         *
+         * we cannot simply called update_context_time()
+         * because of locking issue as we are called in
+         * NMI context
+         */
+        if (read_format & PERF_FORMAT_TOTAL_TIMES) {
+                now = perf_clock();
+                ctx_time = event->shadow_ctx_time + now;
+                enabled = ctx_time - event->tstamp_enabled;
+                running = ctx_time - event->tstamp_running;
+        }
+
         if (event->attr.read_format & PERF_FORMAT_GROUP)
-                perf_output_read_group(handle, event);
+                perf_output_read_group(handle, event, enabled, running);
         else
-                perf_output_read_one(handle, event);
+                perf_output_read_one(handle, event, enabled, running);
 }
 
 void perf_output_sample(struct perf_output_handle *handle,
@@ -5651,7 +5707,7 @@ SYSCALL_DEFINE5(perf_event_open,
         mutex_unlock(&ctx->mutex);
 
         event->owner = current;
-        get_task_struct(current);
+
         mutex_lock(&current->perf_event_mutex);
         list_add_tail(&event->owner_entry, &current->perf_event_list);
         mutex_unlock(&current->perf_event_mutex);
@@ -5719,12 +5775,6 @@ perf_event_create_kernel_counter(struct perf_event_attr *attr, int cpu,
         ++ctx->generation;
         mutex_unlock(&ctx->mutex);
 
-        event->owner = current;
-        get_task_struct(current);
-        mutex_lock(&current->perf_event_mutex);
-        list_add_tail(&event->owner_entry, &current->perf_event_list);
-        mutex_unlock(&current->perf_event_mutex);
-
         return event;
 
 err_free:
@@ -5875,8 +5925,24 @@ again:
  */
 void perf_event_exit_task(struct task_struct *child)
 {
+        struct perf_event *event, *tmp;
         int ctxn;
 
+        mutex_lock(&child->perf_event_mutex);
+        list_for_each_entry_safe(event, tmp, &child->perf_event_list,
+                                 owner_entry) {
+                list_del_init(&event->owner_entry);
+
+                /*
+                 * Ensure the list deletion is visible before we clear
+                 * the owner, closes a race against perf_release() where
+                 * we need to serialize on the owner->perf_event_mutex.
+                 */
+                smp_wmb();
+                event->owner = NULL;
+        }
+        mutex_unlock(&child->perf_event_mutex);
+
         for_each_task_context_nr(ctxn)
                 perf_event_exit_task_context(child, ctxn);
 }
@@ -6295,6 +6361,8 @@ perf_cpu_notify(struct notifier_block *self, unsigned long action, void *hcpu)
 
 void __init perf_event_init(void)
 {
+        int ret;
+
         perf_event_init_all_cpus();
         init_srcu_struct(&pmus_srcu);
         perf_pmu_register(&perf_swevent);
@@ -6302,4 +6370,7 @@ void __init perf_event_init(void)
         perf_pmu_register(&perf_task_clock);
         perf_tp_register();
         perf_cpu_notifier(perf_cpu_notify);
+
+        ret = init_hw_breakpoint();
+        WARN(ret, "hw_breakpoint initialization failed with: %d", ret);
 }