s390: switch to saner kernel_execve() semantics

Acked-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

arch/s390/Kconfig

@@ -136,6 +136,7 @@ config S390
 	select KTIME_SCALAR if 32BIT
 	select HAVE_ARCH_SECCOMP_FILTER
 	select GENERIC_KERNEL_THREAD
+	select GENERIC_KERNEL_EXECVE
 	select HAVE_MOD_ARCH_SPECIFIC
 	select MODULES_USE_ELF_RELA
 

arch/s390/include/asm/unistd.h

@@ -54,7 +54,6 @@
 #   define __ARCH_WANT_COMPAT_SYS_RT_SIGSUSPEND
 # endif
 #define __ARCH_WANT_SYS_EXECVE
-#define __ARCH_WANT_KERNEL_EXECVE
 
 /*
  * "Conditional" syscalls

arch/s390/kernel/entry.S

@@ -330,40 +330,18 @@ ENTRY(ret_from_fork)
 	la	%r11,STACK_FRAME_OVERHEAD(%r15)
 	l	%r12,__LC_THREAD_INFO
 	l	%r13,__LC_SVC_NEW_PSW+4
-	tm	__PT_PSW+1(%r11),0x01	# forking a kernel thread ?
-	je	1f
 	l	%r1,BASED(.Lschedule_tail)
 	basr	%r14,%r1		# call schedule_tail
 	TRACE_IRQS_ON
 	ssm	__LC_SVC_NEW_PSW	# reenable interrupts
-	j	sysc_tracenogo
-
-1:	# it's a kernel thread
-	st	%r15,__PT_R15(%r11)	# store stack pointer for new kthread
-	l	%r1,BASED(.Lschedule_tail)
-	basr	%r14,%r1		# call schedule_tail
-	TRACE_IRQS_ON
-	ssm	__LC_SVC_NEW_PSW	# reenable interrupts
-	lm	%r9,%r11,__PT_R9(%r11)	# load gprs
+	tm	__PT_PSW+1(%r11),0x01	# forking a kernel thread ?
+	jne	sysc_tracenogo
+	# it's a kernel thread
+	lm	%r9,%r10,__PT_R9(%r11)	# load gprs
 ENTRY(kernel_thread_starter)
 	la	%r2,0(%r10)
 	basr	%r14,%r9
-	la	%r2,0
-	br	%r11			# do_exit
-
-#
-# kernel_execve function needs to deal with pt_regs that is not
-# at the usual place
-#
-ENTRY(ret_from_kernel_execve)
-	ssm	__LC_PGM_NEW_PSW	# disable I/O and ext. interrupts
-	lr	%r15,%r2
-	lr	%r11,%r2
-	ahi	%r15,-STACK_FRAME_OVERHEAD
-	xc	__SF_BACKCHAIN(4,%r15),__SF_BACKCHAIN(%r15)
-	l	%r12,__LC_THREAD_INFO
-	ssm	__LC_SVC_NEW_PSW	# reenable interrupts
-	j	sysc_return
+	j	sysc_tracenogo
 
 /*
  * Program check handler routine

arch/s390/kernel/entry64.S

@@ -352,33 +352,17 @@ sysc_tracenogo:
 ENTRY(ret_from_fork)
 	la	%r11,STACK_FRAME_OVERHEAD(%r15)
 	lg	%r12,__LC_THREAD_INFO
-	tm	__PT_PSW+1(%r11),0x01	# forking a kernel thread ?
-	je	1f
 	brasl	%r14,schedule_tail
 	TRACE_IRQS_ON
 	ssm	__LC_SVC_NEW_PSW	# reenable interrupts
-	j	sysc_tracenogo
-1:	# it's a kernel thread
-	stg	%r15,__PT_R15(%r11)	# store stack pointer for new kthread
-	brasl	%r14,schedule_tail
-	TRACE_IRQS_ON
-	ssm	__LC_SVC_NEW_PSW	# reenable interrupts
-	lmg	%r9,%r11,__PT_R9(%r11)	# load gprs
+	tm	__PT_PSW+1(%r11),0x01	# forking a kernel thread ?
+	jne	sysc_tracenogo
+	# it's a kernel thread
+	lmg	%r9,%r10,__PT_R9(%r11)	# load gprs
 ENTRY(kernel_thread_starter)
 	la	%r2,0(%r10)
 	basr	%r14,%r9
-	la	%r2,0
-	br	%r11			# do_exit
-
-ENTRY(ret_from_kernel_execve)
-	ssm	__LC_PGM_NEW_PSW	# disable I/O and ext. interrupts
-	lgr	%r15,%r2
-	lgr	%r11,%r2
-	aghi	%r15,-STACK_FRAME_OVERHEAD
-	xc	__SF_BACKCHAIN(8,%r15),__SF_BACKCHAIN(%r15)
-	lg	%r12,__LC_THREAD_INFO
-	ssm	__LC_SVC_NEW_PSW	# reenable interrupts
-	j	sysc_return
+	j	sysc_tracenogo
 
 /*
  * Program check handler routine