Merge tag 'trace-fixes-v4.0-rc2-2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace

Pull seq-buf/ftrace fixes from Steven Rostedt:
 "This includes fixes for seq_buf_bprintf() truncation issue.  It also
  contains fixes to ftrace when /proc/sys/kernel/ftrace_enabled and
  function tracing are started.  Doing the following causes some issues:

    # echo 0 > /proc/sys/kernel/ftrace_enabled
    # echo function_graph > /sys/kernel/debug/tracing/current_tracer
    # echo 1 > /proc/sys/kernel/ftrace_enabled
    # echo nop > /sys/kernel/debug/tracing/current_tracer
    # echo function_graph > /sys/kernel/debug/tracing/current_tracer

  As well as with function tracing too.  Pratyush Anand first reported
  this issue to me and supplied a patch.  When I tested this on my x86
  test box, it caused thousands of backtraces and warnings to appear in
  dmesg, which also caused a denial of service (a warning for every
  function that was listed).  I applied Pratyush's patch but it did not
  fix the issue for me.  I looked into it and found a slight problem
  with trampoline accounting.  I fixed it and sent Pratyush a patch, but
  he said that it did not fix the issue for him.

  I later learned tha Pratyush was using an ARM64 server, and when I
  tested on my ARM board, I was able to reproduce the same issue as
  Pratyush.  After applying his patch, it fixed the problem.  The above
  test uncovered two different bugs, one in x86 and one in ARM and
  ARM64.  As this looked like it would affect PowerPC, I tested it on my
  PPC64 box.  It too broke, but neither the patch that fixed ARM or x86
  fixed this box (the changes were all in generic code!).  The above
  test, uncovered two more bugs that affected PowerPC.  Again, the
  changes were only done to generic code.  It's the way the arch code
  expected things to be done that was different between the archs.  Some
  where more sensitive than others.

  The rest of this series fixes the PPC bugs as well"

* tag 'trace-fixes-v4.0-rc2-2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
  ftrace: Fix ftrace enable ordering of sysctl ftrace_enabled
  ftrace: Fix en(dis)able graph caller when en(dis)abling record via sysctl
  ftrace: Clear REGS_EN and TRAMP_EN flags on disabling record via sysctl
  seq_buf: Fix seq_buf_bprintf() truncation
  seq_buf: Fix seq_buf_vprintf() truncation

kernel/trace/ftrace.c

@@ -1059,6 +1059,12 @@ static __init void ftrace_profile_debugfs(struct dentry *d_tracer)
 
 static struct pid * const ftrace_swapper_pid = &init_struct_pid;
 
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+static int ftrace_graph_active;
+#else
+# define ftrace_graph_active 0
+#endif
+
 #ifdef CONFIG_DYNAMIC_FTRACE
 
 static struct ftrace_ops *removed_ops;
@@ -2041,8 +2047,12 @@ static int ftrace_check_record(struct dyn_ftrace *rec, int enable, int update)
 		if (!ftrace_rec_count(rec))
 			rec->flags = 0;
 		else
-			/* Just disable the record (keep REGS state) */
-			rec->flags &= ~FTRACE_FL_ENABLED;
+			/*
+			 * Just disable the record, but keep the ops TRAMP
+			 * and REGS states. The _EN flags must be disabled though.
+			 */
+			rec->flags &= ~(FTRACE_FL_ENABLED | FTRACE_FL_TRAMP_EN |
+					FTRACE_FL_REGS_EN);
 	}
 
 	return FTRACE_UPDATE_MAKE_NOP;
@@ -2688,24 +2698,36 @@ static int ftrace_shutdown(struct ftrace_ops *ops, int command)
 
 static void ftrace_startup_sysctl(void)
 {
+	int command;
+
 	if (unlikely(ftrace_disabled))
 		return;
 
 	/* Force update next time */
 	saved_ftrace_func = NULL;
 	/* ftrace_start_up is true if we want ftrace running */
-	if (ftrace_start_up)
-		ftrace_run_update_code(FTRACE_UPDATE_CALLS);
+	if (ftrace_start_up) {
+		command = FTRACE_UPDATE_CALLS;
+		if (ftrace_graph_active)
+			command |= FTRACE_START_FUNC_RET;
+		ftrace_startup_enable(command);
+	}
 }
 
 static void ftrace_shutdown_sysctl(void)
 {
+	int command;
+
 	if (unlikely(ftrace_disabled))
 		return;
 
 	/* ftrace_start_up is true if ftrace is running */
-	if (ftrace_start_up)
-		ftrace_run_update_code(FTRACE_DISABLE_CALLS);
+	if (ftrace_start_up) {
+		command = FTRACE_DISABLE_CALLS;
+		if (ftrace_graph_active)
+			command |= FTRACE_STOP_FUNC_RET;
+		ftrace_run_update_code(command);
+	}
 }
 
 static cycle_t		ftrace_update_time;
@@ -5558,12 +5580,12 @@ ftrace_enable_sysctl(struct ctl_table *table, int write,
 
 	if (ftrace_enabled) {
 
-		ftrace_startup_sysctl();
-
 		/* we are starting ftrace again */
 		if (ftrace_ops_list != &ftrace_list_end)
 			update_ftrace_function();
 
+		ftrace_startup_sysctl();
+
 	} else {
 		/* stopping ftrace calls (just send to ftrace_stub) */
 		ftrace_trace_function = ftrace_stub;
@@ -5590,8 +5612,6 @@ static struct ftrace_ops graph_ops = {
 	ASSIGN_OPS_HASH(graph_ops, &global_ops.local_hash)
 };
 
-static int ftrace_graph_active;
-
 int ftrace_graph_entry_stub(struct ftrace_graph_ent *trace)
 {
 	return 0;

lib/seq_buf.c

@@ -61,7 +61,7 @@ int seq_buf_vprintf(struct seq_buf *s, const char *fmt, va_list args)
 
 	if (s->len < s->size) {
 		len = vsnprintf(s->buffer + s->len, s->size - s->len, fmt, args);
-		if (seq_buf_can_fit(s, len)) {
+		if (s->len + len < s->size) {
 			s->len += len;
 			return 0;
 		}
@@ -118,7 +118,7 @@ int seq_buf_bprintf(struct seq_buf *s, const char *fmt, const u32 *binary)
 
 	if (s->len < s->size) {
 		ret = bstr_printf(s->buffer + s->len, len, fmt, binary);
-		if (seq_buf_can_fit(s, ret)) {
+		if (s->len + ret < s->size) {
 			s->len += ret;
 			return 0;
 		}