From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from foss.arm.com ([217.140.101.70]:55651 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751304AbbHTKva (ORCPT ); Thu, 20 Aug 2015 06:51:30 -0400 Date: Thu, 20 Aug 2015 11:51:27 +0100 From: Will Deacon To: Hanjun Guo Cc: Catalin Marinas , Larry Bassel , Kevin Hilman , "stable@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" Subject: Re: [PATCH] arm64: entry: always restore x0 from the stack on syscall return Message-ID: <20150820105127.GE19328@arm.com> References: <1439996989-5772-1-git-send-email-will.deacon@arm.com> <20150819160320.GI24062@e104818-lin.cambridge.arm.com> <20150819162359.GA10297@arm.com> <20150819163504.GL24062@e104818-lin.cambridge.arm.com> <20150819165643.GD10297@arm.com> <55D592E4.50609@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <55D592E4.50609@linaro.org> Sender: stable-owner@vger.kernel.org List-ID: On Thu, Aug 20, 2015 at 09:42:12AM +0100, Hanjun Guo wrote: > On 08/20/2015 12:56 AM, Will Deacon wrote: > > On Wed, Aug 19, 2015 at 05:35:05PM +0100, Catalin Marinas wrote: > >> 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: > >>>> 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 > >> > >> (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 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