s390: 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: NDmitry Safonov <dima@arista.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Link: http://lkml.kernel.org/r/20200418201944.482088-29-dima@arista.comSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

arch/s390/kernel/dumpstack.c

@@ -126,18 +126,24 @@ int get_stack_info(unsigned long sp, struct task_struct *task,
 	return -EINVAL;
 }
 
-void show_stack(struct task_struct *task, unsigned long *stack)
+void show_stack_loglvl(struct task_struct *task, unsigned long *stack,
+		       const char *loglvl)
 {
 	struct unwind_state state;
 
-	printk("Call Trace:\n");
+	printk("%sCall Trace:\n", loglvl);
 	unwind_for_each_frame(&state, task, NULL, (unsigned long) stack)
-		printk(state.reliable ? " [<%016lx>] %pSR \n" :
-					"([<%016lx>] %pSR)\n",
-		       state.ip, (void *) state.ip);
+		printk(state.reliable ? "%s [<%016lx>] %pSR \n" :
+					"%s([<%016lx>] %pSR)\n",
+		       loglvl, state.ip, (void *) state.ip);
 	debug_show_held_locks(task ? : current);
 }
 
+void show_stack(struct task_struct *task, unsigned long *stack)
+{
+	show_stack_loglvl(task, stack, KERN_DEFAULT);
+}
+
 static void show_last_breaking_event(struct pt_regs *regs)
 {
 	printk("Last Breaking-Event-Address:\n");