c6x: add show_stack_loglvl()

Currently, the log-level of show_stack() depends on a platform
realization.  It creates situations where the headers are printed with
lower log level or higher than the stacktrace (depending on a platform or
user).

Furthermore, it forces the logic decision from user to an architecture
side.  In result, some users as sysrq/kdb/etc are doing tricks with
temporary rising console_loglevel while printing their messages.  And in
result it not only may print unwanted messages from other CPUs, but also
omit printing at all in the unlucky case where the printk() was deferred.

Introducing log-level parameter and KERN_UNSUPPRESSED [1] seems an easier
approach than introducing more printk buffers.  Also, it will consolidate
printings with headers.

Introduce show_stack_loglvl(), that eventually will substitute
show_stack().

[1]: https://lore.kernel.org/lkml/20190528002412.1625-1-dima@arista.com/T/#uSigned-off-by: Dmitry Safonov <dima@arista.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Aurelien Jacquiot <jacquiot.aurelien@gmail.com>
Cc: Mark Salter <msalter@redhat.com>
Link: http://lkml.kernel.org/r/20200418201944.482088-12-dima@arista.comSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/c6x/kernel/traps.c

@@ -344,12 +344,13 @@ asmlinkage int process_exception(struct pt_regs *regs)
 
 static int kstack_depth_to_print = 48;
 
-static void show_trace(unsigned long *stack, unsigned long *endstack)
+static void show_trace(unsigned long *stack, unsigned long *endstack,
+		       const char *loglvl)
 {
 	unsigned long addr;
 	int i;
 
-	pr_debug("Call trace:");
+	printk("%sCall trace:", loglvl);
 	i = 0;
 	while (stack + 1 <= endstack) {
 		addr = *stack++;
@@ -364,16 +365,17 @@ static void show_trace(unsigned long *stack, unsigned long *endstack)
 		if (__kernel_text_address(addr)) {
 #ifndef CONFIG_KALLSYMS
 			if (i % 5 == 0)
-				pr_debug("\n	    ");
+				printk("%s\n	    ", loglvl);
 #endif
-			pr_debug(" [<%08lx>] %pS\n", addr, (void *)addr);
+			printk("%s [<%08lx>] %pS\n", loglvl, addr, (void *)addr);
 			i++;
 		}
 	}
-	pr_debug("\n");
+	printk("%s\n", loglvl);
 }
 
-void show_stack(struct task_struct *task, unsigned long *stack)
+void show_stack_loglvl(struct task_struct *task, unsigned long *stack,
+		const char *loglvl)
 {
 	unsigned long *p, *endstack;
 	int i;
@@ -398,7 +400,12 @@ void show_stack(struct task_struct *task, unsigned long *stack)
 		pr_cont(" %08lx", *p++);
 	}
 	pr_cont("\n");
-	show_trace(stack, endstack);
+	show_trace(stack, endstack, loglvl);
+}
+
+void show_stack(struct task_struct *task, unsigned long *stack)
+{
+	show_stack_loglvl(task, stack, KERN_DEBUG);
 }
 
 int is_valid_bugaddr(unsigned long addr)