ftrace: Add more information to ftrace_bug() output

With the introduction of the dynamic trampolines, it is useful that if
things go wrong that ftrace_bug() produces more information about what
the current state is. This can help debug issues that may arise.

Ftrace has lots of checks to make sure that the state of the system it
touchs is exactly what it expects it to be. When it detects an abnormality
it calls ftrace_bug() and disables itself to prevent any further damage.
It is crucial that ftrace_bug() produces sufficient information that
can be used to debug the situation.

Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Acked-by: Borislav Petkov <bp@suse.de>
Tested-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Tested-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

arch/powerpc/kernel/ftrace.c

@@ -449,7 +449,7 @@ void ftrace_replace_code(int enable)
 		rec = ftrace_rec_iter_record(iter);
 		ret = __ftrace_replace_code(rec, enable);
 		if (ret) {
-			ftrace_bug(ret, rec->ip);
+			ftrace_bug(ret, rec);
 			return;
 		}
 	}

arch/x86/kernel/ftrace.c

@@ -583,7 +583,7 @@ void ftrace_replace_code(int enable)
 
  remove_breakpoints:
 	pr_warn("Failed on %s (%d):\n", report, count);
-	ftrace_bug(ret, rec ? rec->ip : 0);
+	ftrace_bug(ret, rec);
 	for_ftrace_rec_iter(iter) {
 		rec = ftrace_rec_iter_record(iter);
 		/*

include/linux/ftrace.h

@@ -263,7 +263,9 @@ struct ftrace_func_command {
 int ftrace_arch_code_modify_prepare(void);
 int ftrace_arch_code_modify_post_process(void);
 
-void ftrace_bug(int err, unsigned long ip);
+struct dyn_ftrace;
+
+void ftrace_bug(int err, struct dyn_ftrace *rec);
 
 struct seq_file;
 

kernel/trace/ftrace.c

@@ -1738,10 +1738,13 @@ static void print_ip_ins(const char *fmt, unsigned char *p)
 		printk(KERN_CONT "%s%02x", i ? ":" : "", p[i]);
 }
 
+static struct ftrace_ops *
+ftrace_find_tramp_ops_any(struct dyn_ftrace *rec);
+
 /**
  * ftrace_bug - report and shutdown function tracer
  * @failed: The failed type (EFAULT, EINVAL, EPERM)
- * @ip: The address that failed
+ * @rec: The record that failed
  *
  * The arch code that enables or disables the function tracing
  * can call ftrace_bug() when it has detected a problem in
@@ -1750,8 +1753,10 @@ static void print_ip_ins(const char *fmt, unsigned char *p)
  * EINVAL - if what is read at @ip is not what was expected
  * EPERM - if the problem happens on writting to the @ip address
  */
-void ftrace_bug(int failed, unsigned long ip)
+void ftrace_bug(int failed, struct dyn_ftrace *rec)
 {
+	unsigned long ip = rec ? rec->ip : 0;
+
 	switch (failed) {
 	case -EFAULT:
 		FTRACE_WARN_ON_ONCE(1);
@@ -1763,7 +1768,7 @@ void ftrace_bug(int failed, unsigned long ip)
 		pr_info("ftrace failed to modify ");
 		print_ip_sym(ip);
 		print_ip_ins(" actual: ", (unsigned char *)ip);
-		printk(KERN_CONT "\n");
+		pr_cont("\n");
 		break;
 	case -EPERM:
 		FTRACE_WARN_ON_ONCE(1);
@@ -1775,6 +1780,24 @@ void ftrace_bug(int failed, unsigned long ip)
 		pr_info("ftrace faulted on unknown error ");
 		print_ip_sym(ip);
 	}
+	if (rec) {
+		struct ftrace_ops *ops = NULL;
+
+		pr_info("ftrace record flags: %lx\n", rec->flags);
+		pr_cont(" (%ld)%s", ftrace_rec_count(rec),
+			rec->flags & FTRACE_FL_REGS ? " R" : "  ");
+		if (rec->flags & FTRACE_FL_TRAMP_EN) {
+			ops = ftrace_find_tramp_ops_any(rec);
+			if (ops)
+				pr_cont("\ttramp: %pS",
+					(void *)ops->trampoline);
+			else
+				pr_cont("\ttramp: ERROR!");
+
+		}
+		ip = ftrace_get_addr_curr(rec);
+		pr_cont(" expected tramp: %lx\n", ip);
+	}
 }
 
 static int ftrace_check_record(struct dyn_ftrace *rec, int enable, int update)
@@ -2097,7 +2120,7 @@ void __weak ftrace_replace_code(int enable)
 	do_for_each_ftrace_rec(pg, rec) {
 		failed = __ftrace_replace_code(rec, enable);
 		if (failed) {
-			ftrace_bug(failed, rec->ip);
+			ftrace_bug(failed, rec);
 			/* Stop processing */
 			return;
 		}
@@ -2179,17 +2202,14 @@ struct dyn_ftrace *ftrace_rec_iter_record(struct ftrace_rec_iter *iter)
 static int
 ftrace_code_disable(struct module *mod, struct dyn_ftrace *rec)
 {
-	unsigned long ip;
 	int ret;
 
-	ip = rec->ip;
-
 	if (unlikely(ftrace_disabled))
 		return 0;
 
 	ret = ftrace_make_nop(mod, rec, MCOUNT_ADDR);
 	if (ret) {
-		ftrace_bug(ret, ip);
+		ftrace_bug(ret, rec);
 		return 0;
 	}
 	return 1;
@@ -2633,7 +2653,7 @@ static int ftrace_update_code(struct module *mod, struct ftrace_page *new_pgs)
 			if (ftrace_start_up && cnt) {
 				int failed = __ftrace_replace_code(p, 1);
 				if (failed)
-					ftrace_bug(failed, p->ip);
+					ftrace_bug(failed, p);
 			}
 		}
 	}