[PATCH] s390: packed stack vs. cpu hotplug.

The different stack frame layout for packed stacks broke cpu hotplug.
Recreate the initial stack frame of the idle thread for offline cpus coming
back online.  Reenable interrupts after loading the initial registers.  In
addition this patch contains two more bug fixes: a typo for 64 bit
(__SMALL_STACK_SIZE vs.  __SMALL_STACK) and show_trace didn't show a trace
if for task == NULL.
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/s390/kernel/entry.S

@@ -602,8 +602,8 @@ restart_int_handler:
         l       %r15,__LC_SAVE_AREA+60 # load ksp
         lctl    %c0,%c15,__LC_CREGS_SAVE_AREA # get new ctl regs
         lam     %a0,%a15,__LC_AREGS_SAVE_AREA
-        stosm   0(%r15),0x04           # now we can turn dat on
         lm      %r6,%r15,__SF_GPRS(%r15) # load registers from clone
+        stosm   __SF_EMPTY(%r15),0x04    # now we can turn dat on
         basr    %r14,0
         l       %r14,restart_addr-.(%r14)
         br      %r14                   # branch to start_secondary

arch/s390/kernel/entry64.S

@@ -644,8 +644,8 @@ restart_int_handler:
         lctlg   %c0,%c15,0(%r10) # get new ctl regs
         lghi    %r10,__LC_AREGS_SAVE_AREA
         lam     %a0,%a15,0(%r10)
-        stosm   0(%r15),0x04           # now we can turn dat on
         lmg     %r6,%r15,__SF_GPRS(%r15) # load registers from clone
+        stosm   __SF_EMPTY(%r15),0x04    # now we can turn dat on
 	jg      start_secondary
 #else
 /*

arch/s390/kernel/smp.c

@@ -637,6 +637,7 @@ __cpu_up(unsigned int cpu)
 {
 	struct task_struct *idle;
         struct _lowcore    *cpu_lowcore;
+	struct stack_frame *sf;
         sigp_ccode          ccode;
 	int                 curr_cpu;
 
@@ -660,9 +661,14 @@ __cpu_up(unsigned int cpu)
 
 	idle = current_set[cpu];
         cpu_lowcore = lowcore_ptr[cpu];
-	cpu_lowcore->save_area[15] = idle->thread.ksp;
 	cpu_lowcore->kernel_stack = (unsigned long)
 		idle->thread_info + (THREAD_SIZE);
+	sf = (struct stack_frame *) (cpu_lowcore->kernel_stack
+				     - sizeof(struct pt_regs)
+				     - sizeof(struct stack_frame));
+	memset(sf, 0, sizeof(struct stack_frame));
+	sf->gprs[9] = (unsigned long) sf;
+	cpu_lowcore->save_area[15] = (unsigned long) sf;
 	__ctl_store(cpu_lowcore->cregs_save_area[0], 0, 15);
 	__asm__ __volatile__("stam  0,15,0(%0)"
 			     : : "a" (&cpu_lowcore->access_regs_save_area)

arch/s390/kernel/traps.c

@@ -138,8 +138,8 @@ void show_trace(struct task_struct *task, unsigned long * stack)
 		__show_trace(sp, (unsigned long) task->thread_info,
 			     (unsigned long) task->thread_info + THREAD_SIZE);
 	else
-		__show_trace(sp, S390_lowcore.thread_info - THREAD_SIZE,
-			     S390_lowcore.thread_info);
+		__show_trace(sp, S390_lowcore.thread_info,
+			     S390_lowcore.thread_info + THREAD_SIZE);
 	printk("\n");
 }
 

include/asm-s390/thread_info.h

@@ -23,7 +23,7 @@
 #define ASYNC_ORDER  0
 #endif
 #else /* __s390x__ */
-#ifndef __SMALL_STACK_STACK
+#ifndef __SMALL_STACK
 #define THREAD_ORDER 2
 #define ASYNC_ORDER  2
 #else