printk: introduce dump_stack_lvl()

dump_stack() is used for many different cases, which may require a log
level consistent with other kernel messages surrounding the dump_stack()
call.  Without that, certain systems that are configured to ignore the
default level messages will miss stack traces in critical error reports.

This patch introduces dump_stack_lvl() that behaves similarly to
dump_stack(), but accepts a custom log level.  The old dump_stack()
becomes equal to dump_stack_lvl(KERN_DEFAULT).

A somewhat similar patch has been proposed in 2012:
https://lore.kernel.org/lkml/1332493269.2359.9.camel@hebo/ , but wasn't
merged.

[elver@google.com: add missing dump_stack_lvl() stub if CONFIG_PRINTK=n]
  Link: https://lkml.kernel.org/r/YJ0KAM0hQev1AmWe@elver.google.com

Link: https://lkml.kernel.org/r/20210506105405.3535023-1-glider@google.comSigned-off-by: Alexander Potapenko <glider@google.com>
Reviewed-by: Marco Elver <elver@google.com>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: he, bo <bo.he@intel.com>
Cc: Yanmin Zhang <yanmin_zhang@linux.intel.com>
Cc: Prasad Sodagudi <psodagud@quicinc.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/printk.h

@@ -206,6 +206,7 @@ void __init setup_log_buf(int early);
 __printf(1, 2) void dump_stack_set_arch_desc(const char *fmt, ...);
 void dump_stack_print_info(const char *log_lvl);
 void show_regs_print_info(const char *log_lvl);
+extern asmlinkage void dump_stack_lvl(const char *log_lvl) __cold;
 extern asmlinkage void dump_stack(void) __cold;
 extern void printk_safe_flush(void);
 extern void printk_safe_flush_on_panic(void);
@@ -269,6 +270,10 @@ static inline void show_regs_print_info(const char *log_lvl)
 {
 }
 
+static inline void dump_stack_lvl(const char *log_lvl)
+{
+}
+
 static inline void dump_stack(void)
 {
 }

lib/dump_stack.c

@@ -73,10 +73,10 @@ void show_regs_print_info(const char *log_lvl)
 	dump_stack_print_info(log_lvl);
 }
 
-static void __dump_stack(void)
+static void __dump_stack(const char *log_lvl)
 {
-	dump_stack_print_info(KERN_DEFAULT);
-	show_stack(NULL, NULL, KERN_DEFAULT);
+	dump_stack_print_info(log_lvl);
+	show_stack(NULL, NULL, log_lvl);
 }
 
 /**
@@ -87,7 +87,7 @@ static void __dump_stack(void)
 #ifdef CONFIG_SMP
 static atomic_t dump_lock = ATOMIC_INIT(-1);
 
-asmlinkage __visible void dump_stack(void)
+asmlinkage __visible void dump_stack_lvl(const char *log_lvl)
 {
 	unsigned long flags;
 	int was_locked;
@@ -117,7 +117,7 @@ asmlinkage __visible void dump_stack(void)
 		goto retry;
 	}
 
-	__dump_stack();
+	__dump_stack(log_lvl);
 
 	if (!was_locked)
 		atomic_set(&dump_lock, -1);
@@ -125,9 +125,15 @@ asmlinkage __visible void dump_stack(void)
 	local_irq_restore(flags);
 }
 #else
-asmlinkage __visible void dump_stack(void)
+asmlinkage __visible void dump_stack_lvl(const char *log_lvl)
 {
-	__dump_stack();
+	__dump_stack(log_lvl);
 }
 #endif
+EXPORT_SYMBOL(dump_stack_lvl);
+
+asmlinkage __visible void dump_stack(void)
+{
+	dump_stack_lvl(KERN_DEFAULT);
+}
 EXPORT_SYMBOL(dump_stack);