arm: add loglvl to unwind_backtrace()

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.

Add log level argument to unwind_backtrace() as a preparation for
introducing show_stack_loglvl().

As a good side-effect arm_syscall() is now printing errors with the same
log level as the backtrace.

[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: Russell King <linux@armlinux.org.uk>
Cc: Will Deacon <will@kernel.org>
Link: http://lkml.kernel.org/r/20200418201944.482088-6-dima@arista.comSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/arm/include/asm/unwind.h

@@ -36,7 +36,8 @@ extern struct unwind_table *unwind_table_add(unsigned long start,
 					     unsigned long text_addr,
 					     unsigned long text_size);
 extern void unwind_table_del(struct unwind_table *tab);
-extern void unwind_backtrace(struct pt_regs *regs, struct task_struct *tsk);
+extern void unwind_backtrace(struct pt_regs *regs, struct task_struct *tsk,
+			     const char *loglvl);
 
 #endif	/* !__ASSEMBLY__ */
 

arch/arm/kernel/traps.c

@@ -204,7 +204,7 @@ static void dump_instr(const char *lvl, struct pt_regs *regs)
 #ifdef CONFIG_ARM_UNWIND
 static inline void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
 {
-	unwind_backtrace(regs, tsk);
+	unwind_backtrace(regs, tsk, KERN_DEFAULT);
 }
 #else
 static void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
@@ -664,10 +664,10 @@ asmlinkage int arm_syscall(int no, struct pt_regs *regs)
 	if (user_debug & UDBG_SYSCALL) {
 		pr_err("[%d] %s: arm syscall %d\n",
 		       task_pid_nr(current), current->comm, no);
-		dump_instr("", regs);
+		dump_instr(KERN_ERR, regs);
 		if (user_mode(regs)) {
 			__show_regs(regs);
-			c_backtrace(frame_pointer(regs), processor_mode(regs), NULL);
+			c_backtrace(frame_pointer(regs), processor_mode(regs), KERN_ERR);
 		}
 	}
 #endif

arch/arm/kernel/unwind.c

@@ -455,7 +455,8 @@ int unwind_frame(struct stackframe *frame)
 	return URC_OK;
 }
 
-void unwind_backtrace(struct pt_regs *regs, struct task_struct *tsk)
+void unwind_backtrace(struct pt_regs *regs, struct task_struct *tsk,
+		      const char *loglvl)
 {
 	struct stackframe frame;
 
@@ -493,7 +494,7 @@ void unwind_backtrace(struct pt_regs *regs, struct task_struct *tsk)
 		urc = unwind_frame(&frame);
 		if (urc < 0)
 			break;
-		dump_backtrace_entry(where, frame.pc, frame.sp - 4, NULL);
+		dump_backtrace_entry(where, frame.pc, frame.sp - 4, loglvl);
 	}
 }