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

···
 
 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;
···
 		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;
···
 
 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;
···
 
 	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) */
···
 #endif
 	ASSIGN_OPS_HASH(graph_ops, &global_ops.local_hash)
 };
-
-static int ftrace_graph_active;
 
 int ftrace_graph_entry_stub(struct ftrace_graph_ent *trace)
 {

lib/seq_buf.c

···
 
 	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;
 		}
···
 
 	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;
 		}