On Wed, Aug 19, 2015 at 05:23:59PM +0100, Will Deacon wrote: > On Wed, Aug 19, 2015 at 05:03:20PM +0100, Catalin Marinas wrote: > > On Wed, Aug 19, 2015 at 04:09:49PM +0100, Will Deacon wrote: > > > @@ -613,13 +609,14 @@ ENDPROC(cpu_switch_to) > > > */ > > > ret_fast_syscall: > > > disable_irq // disable interrupts > > > + str x0, [sp, #S_X0] // returned x0 > > > ldr x1, [tsk, #TI_FLAGS] // re-check for syscall tracing > > > and x2, x1, #_TIF_SYSCALL_WORK > > > cbnz x2, ret_fast_syscall_trace > > > and x2, x1, #_TIF_WORK_MASK > > > - cbnz x2, fast_work_pending > > > + cbnz x2, work_pending > > > enable_step_tsk x1, x2 > > > - kernel_exit 0, ret = 1 > > > + kernel_exit 0 > > > ret_fast_syscall_trace: > > > enable_irq // enable interrupts > > > b __sys_trace_return > > > > 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@xxxxxxx> (or I can take it for 4.2 but I'd like more testing like LTP) -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html