1 files changed, 77 insertions, 16 deletions

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index cb6c0d2af68f..eac7e3364335 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>
 
@@ -1286,8 +1287,6 @@ void __perf_event_task_sched_out(struct task_struct *task,
 {
         int ctxn;
 
-        perf_sw_event(PERF_COUNT_SW_CONTEXT_SWITCHES, 1, 1, NULL, 0);
-
         for_each_task_context_nr(ctxn)
                 perf_event_context_sched_out(task, ctxn, next);
 }
@@ -1621,8 +1620,12 @@ static void rotate_ctx(struct perf_event_context *ctx)
 {
         raw_spin_lock(&ctx->lock);
 
-        /* Rotate the first entry last of non-pinned groups */
-        list_rotate_left(&ctx->flexible_groups);
+        /*
+         * Rotate the first entry last of non-pinned groups. Rotation might be
+         * disabled by the inheritance code.
+         */
+        if (!ctx->rotate_disable)
+                list_rotate_left(&ctx->flexible_groups);
 
         raw_spin_unlock(&ctx->lock);
 }
@@ -2234,11 +2237,6 @@ 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;
@@ -2251,9 +2249,43 @@ 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);
 }
 
@@ -5677,7 +5709,7 @@ 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);
@@ -5745,12 +5777,6 @@ 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:
@@ -5901,8 +5927,24 @@ 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);
 }
@@ -6122,6 +6164,7 @@ int perf_event_init_context(struct task_struct *child, int ctxn)
         struct perf_event *event;
         struct task_struct *parent = current;
         int inherited_all = 1;
+        unsigned long flags;
         int ret = 0;
 
         child->perf_event_ctxp[ctxn] = NULL;
@@ -6162,6 +6205,15 @@ int perf_event_init_context(struct task_struct *child, int ctxn)
                         break;
         }
 
+        /*
+         * We can't hold ctx->lock when iterating the ->flexible_group list due
+         * to allocations, but we need to prevent rotation because
+         * rotate_ctx() will change the list from interrupt context.
+         */
+        raw_spin_lock_irqsave(&parent_ctx->lock, flags);
+        parent_ctx->rotate_disable = 1;
+        raw_spin_unlock_irqrestore(&parent_ctx->lock, flags);
+
         list_for_each_entry(event, &parent_ctx->flexible_groups, group_entry) {
                 ret = inherit_task_group(event, parent, parent_ctx,
                                          child, ctxn, &inherited_all);
@@ -6169,6 +6221,10 @@ int perf_event_init_context(struct task_struct *child, int ctxn)
                         break;
         }
 
+        raw_spin_lock_irqsave(&parent_ctx->lock, flags);
+        parent_ctx->rotate_disable = 0;
+        raw_spin_unlock_irqrestore(&parent_ctx->lock, flags);
+
         child_ctx = child->perf_event_ctxp[ctxn];
 
         if (child_ctx && inherited_all) {
@@ -6321,6 +6377,8 @@ 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);
@@ -6328,4 +6386,7 @@ 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);
 }