powerpc: Fix error path in kernel_thread function

The powerpc 32-bit and 64-bit kernel_thread functions don't properly
propagate errors being returned by the clone syscall.  (In the case of
error, the syscall exit code returns a positive errno in r3 and sets
the CR0[SO] bit.)

This patch fixes that by negating r3 if CR0[SO] is set after the syscall.
Signed-off-by: Josh Poimboeuf <jpoimboe@us.ibm.com>
Signed-off-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>
Acked-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/kernel/misc_32.S

@@ -900,8 +900,10 @@ _GLOBAL(kernel_thread)
 	li	r4,0		/* new sp (unused) */
 	li	r0,__NR_clone
 	sc
-	cmpwi	0,r3,0		/* parent or child? */
-	bne	1f		/* return if parent */
+	bns+	1f		/* did system call indicate error? */
+	neg	r3,r3		/* if so, make return code negative */
+1:	cmpwi	0,r3,0		/* parent or child? */
+	bne	2f		/* return if parent */
 	li	r0,0		/* make top-level stack frame */
 	stwu	r0,-16(r1)
 	mtlr	r30		/* fn addr in lr */
@@ -911,7 +913,7 @@ _GLOBAL(kernel_thread)
 	li	r0,__NR_exit	/* exit if function returns */
 	li	r3,0
 	sc
-1:	lwz	r30,8(r1)
+2:	lwz	r30,8(r1)
 	lwz	r31,12(r1)
 	addi	r1,r1,16
 	blr

arch/powerpc/kernel/misc_64.S

@@ -426,8 +426,10 @@ _GLOBAL(kernel_thread)
 	li	r4,0		/* new sp (unused) */
 	li	r0,__NR_clone
 	sc
-	cmpdi	0,r3,0		/* parent or child? */
-	bne	1f		/* return if parent */
+	bns+	1f		/* did system call indicate error? */
+	neg	r3,r3		/* if so, make return code negative */
+1:	cmpdi	0,r3,0		/* parent or child? */
+	bne	2f		/* return if parent */
 	li	r0,0
 	stdu	r0,-STACK_FRAME_OVERHEAD(r1)
 	ld	r2,8(r29)
@@ -438,7 +440,7 @@ _GLOBAL(kernel_thread)
 	li	r0,__NR_exit	/* exit after child exits */
         li	r3,0
 	sc
-1:	addi	r1,r1,STACK_FRAME_OVERHEAD	
+2:	addi	r1,r1,STACK_FRAME_OVERHEAD
 	ld	r29,-24(r1)
 	ld	r30,-16(r1)
 	blr