powerpc/64s: sreset panic if there is no debugger or crash dump handlers

system_reset_exception does most of its own crash handling now, invoking the debugger or crash dumps if they are registered. If not, then it goes through to die() to print stack traces, and then is supposed to panic (according to comments).

However after die() prints oopses, it does its own handling which doesn't allow system_reset_exception to panic (e.g., it may just kill the current process). This patch causes sreset exceptions to return from die after it prints messages but before acting.

This also stops die from invoking the debugger on 0x100 crashes. system_reset_exception similarly calls the debugger. It had been thought this was harmless (because if the debugger was disabled, neither call would fire, and if it was enabled the first call would return). However in some cases like xmon 'X' command, the debugger returns 0, which currently causes it to be entered again (first in system_reset_exception, then in die), which is confusing.

---
 arch/powerpc/kernel/traps.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

index 1e48d157196a..b0ac57fa5056 100644
@@ -208,6 +208,12 @@ static void oops_end(unsigned long flags, struct pt_regs *regs,
 	}
 	raw_local_irq_restore(flags);
 
+	/*
+	 * system_reset_excption handles debugger, crash dump, panic, for 0x100
+	 */
+	if (TRAP(regs) == 0x100)
+		return;
+
 	crash_fadump(regs, "die oops");
 
 	if (kexec_should_crash(current))

@@ -272,8 +278,13 @@ void die(const char *str, struct pt_regs *regs, long err)
 {
 	unsigned long flags;
 
-	if (debugger(regs))
-		return;
+	/*
+	 * system_reset_excption handles debugger, crash dump, panic, for 0x100
+	 */
+	if (TRAP(regs) != 0x100) {
+		if (debugger(regs))
+			return;
+	}
 
 	flags = oops_begin(regs);
 	if (__die(str, regs, err))

2.16.1

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/d40b6768e45bd9213139b2d91d30c7

cheers