s390: update sampling tag after task pid change

In a multi-threaded program any thread can call execve(). If this
is not done by the thread group leader, the de_thread() function
replaces the pid of the task that calls execve() with the pid of
thread group leader. If the task reaches user space again without
going over __switch_to() the sampling tag is still set to the old
pid.

Define the arch_setup_new_exec function to verify the task pid
and udpate the tag with LPP if it has changed.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/kernel/process.c

@@ -29,6 +29,7 @@
 #include <linux/random.h>
 #include <linux/export.h>
 #include <linux/init_task.h>
+#include <asm/cpu_mf.h>
 #include <asm/io.h>
 #include <asm/processor.h>
 #include <asm/vtimer.h>
@@ -48,6 +49,15 @@ void flush_thread(void)
 {
 }
 
+void arch_setup_new_exec(void)
+{
+	if (S390_lowcore.current_pid != current->pid) {
+		S390_lowcore.current_pid = current->pid;
+		if (test_facility(40))
+			lpp(&S390_lowcore.lpp);
+	}
+}
+
 void arch_release_task_struct(struct task_struct *tsk)
 {
 	runtime_instr_release(tsk);