---

yaml
---
r: 147572
b: refs/heads/master
c: ad3a37d
h: refs/heads/master
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: be1ac0d81d0e3ab655f8c8ade31fb860ef6aa186
+refs/heads/master: ad3a37de81c45f6c20d410ece86004b98f7b6d84

trunk/kernel/perf_counter.c

@@ -919,7 +919,8 @@ static int context_equiv(struct perf_counter_context *ctx1,
 			 struct perf_counter_context *ctx2)
 {
 	return ctx1->parent_ctx && ctx1->parent_ctx == ctx2->parent_ctx
-		&& ctx1->parent_gen == ctx2->parent_gen;
+		&& ctx1->parent_gen == ctx2->parent_gen
+		&& ctx1->parent_gen != ~0ull;
 }
 
 /*
@@ -1339,7 +1340,6 @@ static struct perf_counter_context *find_get_context(pid_t pid, int cpu)
 			put_ctx(parent_ctx);
 			ctx->parent_ctx = NULL;		/* no longer a clone */
 		}
-		++ctx->generation;
 		/*
 		 * Get an extra reference before dropping the lock so that
 		 * this context won't get freed if the task exits.
@@ -1414,6 +1414,7 @@ static int perf_release(struct inode *inode, struct file *file)
 
 	file->private_data = NULL;
 
+	WARN_ON_ONCE(ctx->parent_ctx);
 	mutex_lock(&ctx->mutex);
 	perf_counter_remove_from_context(counter);
 	mutex_unlock(&ctx->mutex);
@@ -1445,6 +1446,7 @@ perf_read_hw(struct perf_counter *counter, char __user *buf, size_t count)
 	if (counter->state == PERF_COUNTER_STATE_ERROR)
 		return 0;
 
+	WARN_ON_ONCE(counter->ctx->parent_ctx);
 	mutex_lock(&counter->child_mutex);
 	values[0] = perf_counter_read(counter);
 	n = 1;
@@ -1504,6 +1506,7 @@ static void perf_counter_for_each_sibling(struct perf_counter *counter,
 	struct perf_counter_context *ctx = counter->ctx;
 	struct perf_counter *sibling;
 
+	WARN_ON_ONCE(ctx->parent_ctx);
 	mutex_lock(&ctx->mutex);
 	counter = counter->group_leader;
 
@@ -1524,6 +1527,7 @@ static void perf_counter_for_each_child(struct perf_counter *counter,
 {
 	struct perf_counter *child;
 
+	WARN_ON_ONCE(counter->ctx->parent_ctx);
 	mutex_lock(&counter->child_mutex);
 	func(counter);
 	list_for_each_entry(child, &counter->child_list, child_list)
@@ -1536,6 +1540,7 @@ static void perf_counter_for_each(struct perf_counter *counter,
 {
 	struct perf_counter *child;
 
+	WARN_ON_ONCE(counter->ctx->parent_ctx);
 	mutex_lock(&counter->child_mutex);
 	perf_counter_for_each_sibling(counter, func);
 	list_for_each_entry(child, &counter->child_list, child_list)
@@ -1741,6 +1746,7 @@ static void perf_mmap_close(struct vm_area_struct *vma)
 {
 	struct perf_counter *counter = vma->vm_file->private_data;
 
+	WARN_ON_ONCE(counter->ctx->parent_ctx);
 	if (atomic_dec_and_mutex_lock(&counter->mmap_count,
 				      &counter->mmap_mutex)) {
 		struct user_struct *user = current_user();
@@ -1788,6 +1794,7 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma)
 	if (vma->vm_pgoff != 0)
 		return -EINVAL;
 
+	WARN_ON_ONCE(counter->ctx->parent_ctx);
 	mutex_lock(&counter->mmap_mutex);
 	if (atomic_inc_not_zero(&counter->mmap_count)) {
 		if (nr_pages != counter->data->nr_pages)
@@ -3349,8 +3356,10 @@ SYSCALL_DEFINE5(perf_counter_open,
 		goto err_free_put_context;
 
 	counter->filp = counter_file;
+	WARN_ON_ONCE(ctx->parent_ctx);
 	mutex_lock(&ctx->mutex);
 	perf_install_in_context(ctx, counter, cpu);
+	++ctx->generation;
 	mutex_unlock(&ctx->mutex);
 
 	counter->owner = current;
@@ -3436,6 +3445,7 @@ inherit_counter(struct perf_counter *parent_counter,
 	/*
 	 * Link this into the parent counter's child list
 	 */
+	WARN_ON_ONCE(parent_counter->ctx->parent_ctx);
 	mutex_lock(&parent_counter->child_mutex);
 	list_add_tail(&child_counter->child_list, &parent_counter->child_list);
 	mutex_unlock(&parent_counter->child_mutex);
@@ -3485,6 +3495,7 @@ static void sync_child_counter(struct perf_counter *child_counter,
 	/*
 	 * Remove this counter from the parent's list
 	 */
+	WARN_ON_ONCE(parent_counter->ctx->parent_ctx);
 	mutex_lock(&parent_counter->child_mutex);
 	list_del_init(&child_counter->child_list);
 	mutex_unlock(&parent_counter->child_mutex);
@@ -3527,12 +3538,17 @@ void perf_counter_exit_task(struct task_struct *child)
 	struct perf_counter_context *child_ctx;
 	unsigned long flags;
 
-	child_ctx = child->perf_counter_ctxp;
-
-	if (likely(!child_ctx))
+	if (likely(!child->perf_counter_ctxp))
 		return;
 
 	local_irq_save(flags);
+	/*
+	 * We can't reschedule here because interrupts are disabled,
+	 * and either child is current or it is a task that can't be
+	 * scheduled, so we are now safe from rescheduling changing
+	 * our context.
+	 */
+	child_ctx = child->perf_counter_ctxp;
 	__perf_counter_task_sched_out(child_ctx);
 
 	/*
@@ -3542,6 +3558,15 @@ void perf_counter_exit_task(struct task_struct *child)
 	 */
 	spin_lock(&child_ctx->lock);
 	child->perf_counter_ctxp = NULL;
+	if (child_ctx->parent_ctx) {
+		/*
+		 * This context is a clone; unclone it so it can't get
+		 * swapped to another process while we're removing all
+		 * the counters from it.
+		 */
+		put_ctx(child_ctx->parent_ctx);
+		child_ctx->parent_ctx = NULL;
+	}
 	spin_unlock(&child_ctx->lock);
 	local_irq_restore(flags);
 
@@ -3571,18 +3596,19 @@ void perf_counter_exit_task(struct task_struct *child)
 int perf_counter_init_task(struct task_struct *child)
 {
 	struct perf_counter_context *child_ctx, *parent_ctx;
+	struct perf_counter_context *cloned_ctx;
 	struct perf_counter *counter;
 	struct task_struct *parent = current;
 	int inherited_all = 1;
+	u64 cloned_gen;
 	int ret = 0;
 
 	child->perf_counter_ctxp = NULL;
 
 	mutex_init(&child->perf_counter_mutex);
 	INIT_LIST_HEAD(&child->perf_counter_list);
 
-	parent_ctx = parent->perf_counter_ctxp;
-	if (likely(!parent_ctx || !parent_ctx->nr_counters))
+	if (likely(!parent->perf_counter_ctxp))
 		return 0;
 
 	/*
@@ -3599,6 +3625,34 @@ int perf_counter_init_task(struct task_struct *child)
 	child->perf_counter_ctxp = child_ctx;
 	get_task_struct(child);
 
+	/*
+	 * If the parent's context is a clone, temporarily set its
+	 * parent_gen to an impossible value (all 1s) so it won't get
+	 * swapped under us.  The rcu_read_lock makes sure that
+	 * parent_ctx continues to exist even if it gets swapped to
+	 * another process and then freed while we are trying to get
+	 * its lock.
+	 */
+	rcu_read_lock();
+ retry:
+	parent_ctx = rcu_dereference(parent->perf_counter_ctxp);
+	/*
+	 * No need to check if parent_ctx != NULL here; since we saw
+	 * it non-NULL earlier, the only reason for it to become NULL
+	 * is if we exit, and since we're currently in the middle of
+	 * a fork we can't be exiting at the same time.
+	 */
+	spin_lock_irq(&parent_ctx->lock);
+	if (parent_ctx != rcu_dereference(parent->perf_counter_ctxp)) {
+		spin_unlock_irq(&parent_ctx->lock);
+		goto retry;
+	}
+	cloned_gen = parent_ctx->parent_gen;
+	if (parent_ctx->parent_ctx)
+		parent_ctx->parent_gen = ~0ull;
+	spin_unlock_irq(&parent_ctx->lock);
+	rcu_read_unlock();
+
 	/*
 	 * Lock the parent list. No need to lock the child - not PID
 	 * hashed yet and not running, so nobody can access it.
@@ -3630,10 +3684,15 @@ int perf_counter_init_task(struct task_struct *child)
 		/*
 		 * Mark the child context as a clone of the parent
 		 * context, or of whatever the parent is a clone of.
+		 * Note that if the parent is a clone, it could get
+		 * uncloned at any point, but that doesn't matter
+		 * because the list of counters and the generation
+		 * count can't have changed since we took the mutex.
 		 */
-		if (parent_ctx->parent_ctx) {
-			child_ctx->parent_ctx = parent_ctx->parent_ctx;
-			child_ctx->parent_gen = parent_ctx->parent_gen;
+		cloned_ctx = rcu_dereference(parent_ctx->parent_ctx);
+		if (cloned_ctx) {
+			child_ctx->parent_ctx = cloned_ctx;
+			child_ctx->parent_gen = cloned_gen;
 		} else {
 			child_ctx->parent_ctx = parent_ctx;
 			child_ctx->parent_gen = parent_ctx->generation;
@@ -3643,6 +3702,16 @@ int perf_counter_init_task(struct task_struct *child)
 
 	mutex_unlock(&parent_ctx->mutex);
 
+	/*
+	 * Restore the clone status of the parent.
+	 */
+	if (parent_ctx->parent_ctx) {
+		spin_lock_irq(&parent_ctx->lock);
+		if (parent_ctx->parent_ctx)
+			parent_ctx->parent_gen = cloned_gen;
+		spin_unlock_irq(&parent_ctx->lock);
+	}
+
 	return ret;
 }