s390: fold kernel_thread_helper() into ret_from_fork()

... and don't bother with syscall return path in case of kernel
threads.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

3 files changed, 28 insertions, 16 deletions

diff --git a/arch/s390/kernel/entry.S b/arch/s390/kernel/entry.S
index 6286985a1039..24de1cd3754b 100644
--- a/arch/s390/kernel/entry.S
+++ b/arch/s390/kernel/entry.S
@@ -331,14 +331,26 @@ ENTRY(ret_from_fork)
         l       %r12,__LC_THREAD_INFO
         l       %r13,__LC_SVC_NEW_PSW+4
         tm      __PT_PSW+1(%r11),0x01   # forking a kernel thread ?
-        jo      0f
-        st      %r15,__PT_R15(%r11)     # store stack pointer for new kthread
-0:      l       %r1,BASED(.Lschedule_tail)
+        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
+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
diff --git a/arch/s390/kernel/entry64.S b/arch/s390/kernel/entry64.S
index 1f776f2edda5..39c84e65f74f 100644
--- a/arch/s390/kernel/entry64.S
+++ b/arch/s390/kernel/entry64.S
@@ -352,12 +352,22 @@ 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 ?
-        jo      0f
-        stg     %r15,__PT_R15(%r11)     # store stack pointer for new kthread
-0:      brasl   %r14,schedule_tail
+        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
+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
diff --git a/arch/s390/kernel/process.c b/arch/s390/kernel/process.c
index e540251e1dd1..2868a364ff94 100644
--- a/arch/s390/kernel/process.c
+++ b/arch/s390/kernel/process.c
@@ -98,16 +98,6 @@ void cpu_idle(void)
 
 extern void __kprobes kernel_thread_starter(void);
 
-asm(
-        ".section .kprobes.text, \"ax\"\n"
-        ".global kernel_thread_starter\n"
-        "kernel_thread_starter:\n"
-        "    la    2,0(10)\n"
-        "    basr  14,9\n"
-        "    la    2,0\n"
-        "    br    11\n"
-        ".previous\n");
-
 int kernel_thread(int (*fn)(void *), void * arg, unsigned long flags)
 {
         struct pt_regs regs;