Small fixes and minor cleanups for Tracing

- Make exported ftrace function not static
  - Fix NULL pointer dereference in reading probes as they are created
  - Fix NULL pointer dereference in k/uprobe clean up path
  - Various documentation fixes
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Merge tag 'trace-v5.3-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace

Pull tracing fixes from Steven Rostedt:
 "Small fixes and minor cleanups for tracing:

   - Make exported ftrace function not static

   - Fix NULL pointer dereference in reading probes as they are created

   - Fix NULL pointer dereference in k/uprobe clean up path

   - Various documentation fixes"

* tag 'trace-v5.3-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
  tracing: Correct kdoc formats
  ftrace/x86: Remove mcount() declaration
  tracing/probe: Fix null pointer dereference
  tracing: Make exported ftrace_set_clr_event non-static
  ftrace: Check for successful allocation of hash
  ftrace: Check for empty hash and comment the race with registering probes
  ftrace: Fix NULL pointer dereference in t_probe_next()

arch/x86/include/asm/ftrace.h

@@ -16,7 +16,6 @@
 #define HAVE_FUNCTION_GRAPH_RET_ADDR_PTR
 
 #ifndef __ASSEMBLY__
-extern void mcount(void);
 extern atomic_t modifying_ftrace_code;
 extern void __fentry__(void);
 

include/linux/trace_events.h

@@ -548,6 +548,7 @@ extern int trace_event_get_offsets(struct trace_event_call *call);
 
 #define is_signed_type(type)	(((type)(-1)) < (type)1)
 
+int ftrace_set_clr_event(struct trace_array *tr, char *buf, int set);
 int trace_set_clr_event(const char *system, const char *event, int set);
 
 /*

kernel/trace/ftrace.c

@@ -3095,6 +3095,14 @@ t_probe_next(struct seq_file *m, loff_t *pos)
 		hnd = &iter->probe_entry->hlist;
 
 	hash = iter->probe->ops.func_hash->filter_hash;
+
+	/*
+	 * A probe being registered may temporarily have an empty hash
+	 * and it's at the end of the func_probes list.
+	 */
+	if (!hash || hash == EMPTY_HASH)
+		return NULL;
+
 	size = 1 << hash->size_bits;
 
  retry:
@@ -4320,12 +4328,21 @@ register_ftrace_function_probe(char *glob, struct trace_array *tr,
 
 	mutex_unlock(&ftrace_lock);
 
+	/*
+	 * Note, there's a small window here that the func_hash->filter_hash
+	 * may be NULL or empty. Need to be carefule when reading the loop.
+	 */
 	mutex_lock(&probe->ops.func_hash->regex_lock);
 
 	orig_hash = &probe->ops.func_hash->filter_hash;
 	old_hash = *orig_hash;
 	hash = alloc_and_copy_ftrace_hash(FTRACE_HASH_DEFAULT_BITS, old_hash);
 
+	if (!hash) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
 	ret = ftrace_match_records(hash, glob, strlen(glob));
 
 	/* Nothing found? */

kernel/trace/trace.c

@@ -1567,9 +1567,9 @@ update_max_tr(struct trace_array *tr, struct task_struct *tsk, int cpu,
 
 /**
  * update_max_tr_single - only copy one trace over, and reset the rest
- * @tr - tracer
- * @tsk - task with the latency
- * @cpu - the cpu of the buffer to copy.
+ * @tr: tracer
+ * @tsk: task with the latency
+ * @cpu: the cpu of the buffer to copy.
  *
  * Flip the trace of a single CPU buffer between the @tr and the max_tr.
  */
@@ -1767,7 +1767,7 @@ static void __init apply_trace_boot_options(void);
 
 /**
  * register_tracer - register a tracer with the ftrace system.
- * @type - the plugin for the tracer
+ * @type: the plugin for the tracer
  *
  * Register a new plugin tracer.
  */
@@ -2230,9 +2230,9 @@ static bool tracing_record_taskinfo_skip(int flags)
 /**
  * tracing_record_taskinfo - record the task info of a task
  *
- * @task  - task to record
- * @flags - TRACE_RECORD_CMDLINE for recording comm
- *        - TRACE_RECORD_TGID for recording tgid
+ * @task:  task to record
+ * @flags: TRACE_RECORD_CMDLINE for recording comm
+ *         TRACE_RECORD_TGID for recording tgid
  */
 void tracing_record_taskinfo(struct task_struct *task, int flags)
 {
@@ -2258,10 +2258,10 @@ void tracing_record_taskinfo(struct task_struct *task, int flags)
 /**
  * tracing_record_taskinfo_sched_switch - record task info for sched_switch
  *
- * @prev - previous task during sched_switch
- * @next - next task during sched_switch
- * @flags - TRACE_RECORD_CMDLINE for recording comm
- *          TRACE_RECORD_TGID for recording tgid
+ * @prev: previous task during sched_switch
+ * @next: next task during sched_switch
+ * @flags: TRACE_RECORD_CMDLINE for recording comm
+ *         TRACE_RECORD_TGID for recording tgid
  */
 void tracing_record_taskinfo_sched_switch(struct task_struct *prev,
 					  struct task_struct *next, int flags)
@@ -3072,7 +3072,9 @@ static void trace_printk_start_stop_comm(int enabled)
 
 /**
  * trace_vbprintk - write binary msg to tracing buffer
- *
+ * @ip:    The address of the caller
+ * @fmt:   The string format to write to the buffer
+ * @args:  Arguments for @fmt
  */
 int trace_vbprintk(unsigned long ip, const char *fmt, va_list args)
 {

kernel/trace/trace_events.c

@@ -787,7 +787,7 @@ static int __ftrace_set_clr_event(struct trace_array *tr, const char *match,
 	return ret;
 }
 
-static int ftrace_set_clr_event(struct trace_array *tr, char *buf, int set)
+int ftrace_set_clr_event(struct trace_array *tr, char *buf, int set)
 {
 	char *event = NULL, *sub = NULL, *match;
 	int ret;

kernel/trace/trace_probe.c

@@ -895,7 +895,8 @@ void trace_probe_cleanup(struct trace_probe *tp)
 	for (i = 0; i < tp->nr_args; i++)
 		traceprobe_free_probe_arg(&tp->args[i]);
 
-	kfree(call->class->system);
+	if (call->class)
+		kfree(call->class->system);
 	kfree(call->name);
 	kfree(call->print_fmt);
 }