arm64: use private ratelimit state along with show_unhandled_signals

printk_ratelimit() shares the ratelimiting state with other callers what
may lead to scenarios where at the time we want to print out debug
information we already limited, so nothing appears in the dmesg - this
makes exception-trace quite poor helper in debugging.

Additionally, we have imbalance with some messages limited with global
ratelimit state and other messages limited with their private state
defined via pr_*_ratelimited().

To address this inconsistency show_unhandled_signals_ratelimited()
macro is introduced and caller sites are converted to use it.
Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/include/asm/system_misc.h

@@ -23,6 +23,8 @@
 #include <linux/compiler.h>
 #include <linux/linkage.h>
 #include <linux/irqflags.h>
+#include <linux/signal.h>
+#include <linux/ratelimit.h>
 #include <linux/reboot.h>
 
 struct pt_regs;
@@ -43,6 +45,17 @@ extern void __show_regs(struct pt_regs *);
 
 extern void (*arm_pm_restart)(enum reboot_mode reboot_mode, const char *cmd);
 
+#define show_unhandled_signals_ratelimited()				\
+({									\
+	static DEFINE_RATELIMIT_STATE(_rs,				\
+				      DEFAULT_RATELIMIT_INTERVAL,	\
+				      DEFAULT_RATELIMIT_BURST);		\
+	bool __show_ratelimited = false;				\
+	if (show_unhandled_signals && __ratelimit(&_rs))		\
+		__show_ratelimited = true;				\
+	__show_ratelimited;						\
+})
+
 #define UDBG_UNDEFINED	(1 << 0)
 #define UDBG_SYSCALL	(1 << 1)
 #define UDBG_BADABORT	(1 << 2)

arch/arm64/kernel/traps.c

@@ -335,8 +335,7 @@ asmlinkage void __exception do_undefinstr(struct pt_regs *regs)
 	if (call_undef_hook(regs) == 0)
 		return;
 
-	if (show_unhandled_signals && unhandled_signal(current, SIGILL) &&
-	    printk_ratelimit()) {
+	if (show_unhandled_signals_ratelimited() && unhandled_signal(current, SIGILL)) {
 		pr_info("%s[%d]: undefined instruction: pc=%p\n",
 			current->comm, task_pid_nr(current), pc);
 		dump_instr(KERN_INFO, regs);
@@ -363,7 +362,7 @@ asmlinkage long do_ni_syscall(struct pt_regs *regs)
 	}
 #endif
 
-	if (show_unhandled_signals && printk_ratelimit()) {
+	if (show_unhandled_signals_ratelimited()) {
 		pr_info("%s[%d]: syscall %d\n", current->comm,
 			task_pid_nr(current), (int)regs->syscallno);
 		dump_instr("", regs);

arch/arm64/mm/fault.c

@@ -115,8 +115,7 @@ static void __do_user_fault(struct task_struct *tsk, unsigned long addr,
 {
 	struct siginfo si;
 
-	if (show_unhandled_signals && unhandled_signal(tsk, sig) &&
-	    printk_ratelimit()) {
+	if (show_unhandled_signals_ratelimited() && unhandled_signal(tsk, sig)) {
 		pr_info("%s[%d]: unhandled %s (%d) at 0x%08lx, esr 0x%03x\n",
 			tsk->comm, task_pid_nr(tsk), fault_name(esr), sig,
 			addr, esr);