On Thu, Aug 20, 2015 at 09:42:12AM +0100, Hanjun Guo wrote:

On 08/20/2015 12:56 AM, Will Deacon wrote:

quoted

On Wed, Aug 19, 2015 at 05:35:05PM +0100, Catalin Marinas wrote:

quoted

On Wed, Aug 19, 2015 at 05:23:59PM +0100, Will Deacon wrote:

quoted

On Wed, Aug 19, 2015 at 05:03:20PM +0100, Catalin Marinas wrote:

quoted

There is another str x0 in __sys_trace_return which I think we could
remove.

Hmm, I don't think we can remove that. It's needed on the slowpath to
update the pt_regs with either -ENOSYS (for __ni_sys_trace) or the
syscall return value from the blr in __sys_trace.

What we can do instead is change the branch above to branch to
__sys_trace_return_skipped. Patch below.

Will

--->8

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 2a5e64ccc991..088322ff1ba0 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S

@@ -619,7 +619,7 @@ ret_fast_syscall:
         kernel_exit 0
  ret_fast_syscall_trace:
         enable_irq                              // enable interrupts
-       b       __sys_trace_return
+       b       __sys_trace_return_skipped      // we already saved x0

That would do. With this added:

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>

(or I can take it for 4.2 but I'd like more testing like LTP)

Yeah, I'll run some tests overnight and see how it holds up.

How is the stress test going on? I didn't do some stress test but
when I applied this patch (along with above additions), the problem
I reported is gone,

Tested-by: Hanjun Guo <redacted>

Thanks, Hanjun. LTP passed successfully, so I think the patch is ok but
there's no need to rush it in for 4.2.

Will