Various fix ups.

- Comment fixes
  - Build fix
  - Better memory alloction (don't use NR_CPUS)
  - Configuration fix
  - Build warning fix
  - Enhanced callback parameter (to simplify users of trace hooks)
  - Give up on stack tracing when RCU isn't watching (it's a lost cause)
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Merge tag 'trace-v4.15-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace

Pull tracing fixes from Steven Rostedt:
 "Various fix-ups:

   - comment fixes

   - build fix

   - better memory alloction (don't use NR_CPUS)

   - configuration fix

   - build warning fix

   - enhanced callback parameter (to simplify users of trace hooks)

   - give up on stack tracing when RCU isn't watching (it's a lost
     cause)"

* tag 'trace-v4.15-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
  tracing: Have stack trace not record if RCU is not watching
  tracing: Pass export pointer as argument to ->write()
  ring-buffer: Remove unused function __rb_data_page_index()
  tracing: make PREEMPTIRQ_EVENTS depend on TRACING
  tracing: Allocate mask_str buffer dynamically
  tracing: always define trace_{irq,preempt}_{enable_disable}
  tracing: Fix code comments in trace.c

drivers/hwtracing/stm/ftrace.c

@@ -42,9 +42,11 @@ static struct stm_ftrace {
  * @len:	length of the data packet
  */
 static void notrace
-stm_ftrace_write(const void *buf, unsigned int len)
+stm_ftrace_write(struct trace_export *export, const void *buf, unsigned int len)
 {
-	stm_source_write(&stm_ftrace.data, STM_FTRACE_CHAN, buf, len);
+	struct stm_ftrace *stm = container_of(export, struct stm_ftrace, ftrace);
+
+	stm_source_write(&stm->data, STM_FTRACE_CHAN, buf, len);
 }
 
 static int stm_ftrace_link(struct stm_source_data *data)

include/linux/trace.h

@@ -18,7 +18,7 @@
  */
 struct trace_export {
 	struct trace_export __rcu	*next;
-	void (*write)(const void *, unsigned int);
+	void (*write)(struct trace_export *, const void *, unsigned int);
 };
 
 int register_ftrace_export(struct trace_export *export);

include/trace/events/preemptirq.h

@@ -56,15 +56,18 @@ DEFINE_EVENT(preemptirq_template, preempt_enable,
 
 #include <trace/define_trace.h>
 
-#else /* !CONFIG_PREEMPTIRQ_EVENTS */
+#endif /* !CONFIG_PREEMPTIRQ_EVENTS */
 
+#if !defined(CONFIG_PREEMPTIRQ_EVENTS) || defined(CONFIG_PROVE_LOCKING)
 #define trace_irq_enable(...)
 #define trace_irq_disable(...)
-#define trace_preempt_enable(...)
-#define trace_preempt_disable(...)
 #define trace_irq_enable_rcuidle(...)
 #define trace_irq_disable_rcuidle(...)
+#endif
+
+#if !defined(CONFIG_PREEMPTIRQ_EVENTS) || !defined(CONFIG_DEBUG_PREEMPT)
+#define trace_preempt_enable(...)
+#define trace_preempt_disable(...)
 #define trace_preempt_enable_rcuidle(...)
 #define trace_preempt_disable_rcuidle(...)
-
 #endif

kernel/trace/Kconfig

@@ -164,6 +164,7 @@ config PREEMPTIRQ_EVENTS
 	bool "Enable trace events for preempt and irq disable/enable"
 	select TRACE_IRQFLAGS
 	depends on DEBUG_PREEMPT || !PROVE_LOCKING
+	depends on TRACING
 	default n
 	help
 	  Enable tracing of disable and enable events for preemption and irqs.

kernel/trace/ring_buffer.c

@@ -1799,12 +1799,6 @@ void ring_buffer_change_overwrite(struct ring_buffer *buffer, int val)
 }
 EXPORT_SYMBOL_GPL(ring_buffer_change_overwrite);
 
-static __always_inline void *
-__rb_data_page_index(struct buffer_data_page *bpage, unsigned index)
-{
-	return bpage->data + index;
-}
-
 static __always_inline void *__rb_page_index(struct buffer_page *bpage, unsigned index)
 {
 	return bpage->page->data + index;

kernel/trace/trace.c

@@ -362,7 +362,7 @@ trace_ignore_this_task(struct trace_pid_list *filtered_pids, struct task_struct
 }
 
 /**
- * trace_pid_filter_add_remove - Add or remove a task from a pid_list
+ * trace_pid_filter_add_remove_task - Add or remove a task from a pid_list
  * @pid_list: The list to modify
  * @self: The current task for fork or NULL for exit
  * @task: The task to add or remove
@@ -925,7 +925,7 @@ static void tracing_snapshot_instance(struct trace_array *tr)
 }
 
 /**
- * trace_snapshot - take a snapshot of the current buffer.
+ * tracing_snapshot - take a snapshot of the current buffer.
  *
  * This causes a swap between the snapshot buffer and the current live
  * tracing buffer. You can use this to take snapshots of the live
@@ -1004,9 +1004,9 @@ int tracing_alloc_snapshot(void)
 EXPORT_SYMBOL_GPL(tracing_alloc_snapshot);
 
 /**
- * trace_snapshot_alloc - allocate and take a snapshot of the current buffer.
+ * tracing_snapshot_alloc - allocate and take a snapshot of the current buffer.
  *
- * This is similar to trace_snapshot(), but it will allocate the
+ * This is similar to tracing_snapshot(), but it will allocate the
  * snapshot buffer if it isn't already allocated. Use this only
  * where it is safe to sleep, as the allocation may sleep.
  *
@@ -1303,7 +1303,7 @@ unsigned long __read_mostly	tracing_thresh;
 /*
  * Copy the new maximum trace into the separate maximum-trace
  * structure. (this way the maximum trace is permanently saved,
- * for later retrieval via /sys/kernel/debug/tracing/latency_trace)
+ * for later retrieval via /sys/kernel/tracing/tracing_max_latency)
  */
 static void
 __update_max_tr(struct trace_array *tr, struct task_struct *tsk, int cpu)
@@ -2415,7 +2415,7 @@ trace_process_export(struct trace_export *export,
 
 	entry = ring_buffer_event_data(event);
 	size = ring_buffer_event_length(event);
-	export->write(entry, size);
+	export->write(export, entry, size);
 }
 
 static DEFINE_MUTEX(ftrace_export_lock);
@@ -4178,37 +4178,30 @@ static const struct file_operations show_traces_fops = {
 	.llseek		= seq_lseek,
 };
 
-/*
- * The tracer itself will not take this lock, but still we want
- * to provide a consistent cpumask to user-space:
- */
-static DEFINE_MUTEX(tracing_cpumask_update_lock);
-
-/*
- * Temporary storage for the character representation of the
- * CPU bitmask (and one more byte for the newline):
- */
-static char mask_str[NR_CPUS + 1];
-
 static ssize_t
 tracing_cpumask_read(struct file *filp, char __user *ubuf,
 		     size_t count, loff_t *ppos)
 {
 	struct trace_array *tr = file_inode(filp)->i_private;
+	char *mask_str;
 	int len;
 
-	mutex_lock(&tracing_cpumask_update_lock);
+	len = snprintf(NULL, 0, "%*pb\n",
+		       cpumask_pr_args(tr->tracing_cpumask)) + 1;
+	mask_str = kmalloc(len, GFP_KERNEL);
+	if (!mask_str)
+		return -ENOMEM;
 
-	len = snprintf(mask_str, count, "%*pb\n",
+	len = snprintf(mask_str, len, "%*pb\n",
 		       cpumask_pr_args(tr->tracing_cpumask));
 	if (len >= count) {
 		count = -EINVAL;
 		goto out_err;
 	}
-	count = simple_read_from_buffer(ubuf, count, ppos, mask_str, NR_CPUS+1);
+	count = simple_read_from_buffer(ubuf, count, ppos, mask_str, len);
 
 out_err:
-	mutex_unlock(&tracing_cpumask_update_lock);
+	kfree(mask_str);
 
 	return count;
 }
@@ -4228,8 +4221,6 @@ tracing_cpumask_write(struct file *filp, const char __user *ubuf,
 	if (err)
 		goto err_unlock;
 
-	mutex_lock(&tracing_cpumask_update_lock);
-
 	local_irq_disable();
 	arch_spin_lock(&tr->max_lock);
 	for_each_tracing_cpu(cpu) {
@@ -4252,8 +4243,6 @@ tracing_cpumask_write(struct file *filp, const char __user *ubuf,
 	local_irq_enable();
 
 	cpumask_copy(tr->tracing_cpumask, tracing_cpumask_new);
-
-	mutex_unlock(&tracing_cpumask_update_lock);
 	free_cpumask_var(tracing_cpumask_new);
 
 	return count;

kernel/trace/trace_stack.c

@@ -209,6 +209,10 @@ stack_trace_call(unsigned long ip, unsigned long parent_ip,
 	if (__this_cpu_read(disable_stack_tracer) != 1)
 		goto out;
 
+	/* If rcu is not watching, then save stack trace can fail */
+	if (!rcu_is_watching())
+		goto out;
+
 	ip += MCOUNT_INSN_SIZE;
 
 	check_stack(ip, &stack);