"Naveen N. Rao" [off-list ref] writes:

On 2017/05/04 04:03PM, Michael Ellerman wrote:

quoted

Would this work?

diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index 767ef6d68c9e..8d0fa4a2262a 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S

@@ -207,6 +207,7 @@ system_call:			/* label this so stack traces look sane */
 	mtmsrd	r11,1
 #endif /* CONFIG_PPC_BOOK3E */

+syscall_exit:
 	ld	r9,TI_FLAGS(r12)
 	li	r11,-MAX_ERRNO
 	andi.	r0,r9,(_TIF_SYSCALL_DOTRACE|_TIF_SINGLESTEP|_TIF_USER_WORK_MASK|_TIF_PERSYSCALL_MASK)

Ah, nice. I previously incorrectly assumed that syscall_exit was not 
desirable throughout this function. Your earlier patch was only about 
what label showed up while _inside_ a syscall.

Yep. When you're somewhere in a syscall the LR on the stack points to
the instruction following the bctrl that called the syscall handler, so
as long as the label preceeding that is system_call then the backtrace
should look good.

We could even just have a nop after the bctrl and then the label, but
that would be a bit gross.

So, syscall_exit post handling of a syscall is fine.

This patch looks fine to me. I will test with this change and get back.

Thanks.

cheers