From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Shi, Yang" Subject: Re: [PATCH] arm64: reenable interrupt when handling ptrace breakpoint Date: Wed, 13 Jan 2016 09:17:46 -0800 Message-ID: <569686BA.6050703@linaro.org> References: <1450225088-2456-1-git-send-email-yang.shi@linaro.org> <20151216111316.GD4308@arm.com> <5671CD5B.9030907@linaro.org> <20151221104818.GF23092@arm.com> <20151221170028.GT23092@arm.com> <56955B3A.5010303@linaro.org> <20160113102622.GC25458@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Cc: Thomas Gleixner , Catalin.Marinas@arm.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linaro-kernel@lists.linaro.org, linux-rt-users@vger.kernel.org To: Will Deacon Return-path: Received: from mail-pf0-f170.google.com ([209.85.192.170]:33071 "EHLO mail-pf0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754278AbcAMRRs (ORCPT ); Wed, 13 Jan 2016 12:17:48 -0500 Received: by mail-pf0-f170.google.com with SMTP id e65so84538798pfe.0 for ; Wed, 13 Jan 2016 09:17:48 -0800 (PST) In-Reply-To: <20160113102622.GC25458@arm.com> Sender: linux-rt-users-owner@vger.kernel.org List-ID: On 1/13/2016 2:26 AM, Will Deacon wrote: > On Tue, Jan 12, 2016 at 11:59:54AM -0800, Shi, Yang wrote: >> On 12/21/2015 9:00 AM, Will Deacon wrote: >>> On Mon, Dec 21, 2015 at 05:51:22PM +0100, Thomas Gleixner wrote: >>>> On Mon, 21 Dec 2015, Will Deacon wrote: >>>>> +static void send_user_sigtrap(int si_code) >>>>> +{ >>>>> + struct pt_regs *regs = current_pt_regs(); >>>>> + siginfo_t info = { >>>>> + .si_signo = SIGTRAP, >>>>> + .si_errno = 0, >>>>> + .si_code = si_code, >>>>> + .si_addr = (void __user *)instruction_pointer(regs), >>>>> + }; >>>>> + >>>>> + if (WARN_ON(!user_mode(regs))) >>>>> + return; >>>>> + >>>>> + preempt_disable(); >>>> >>>> That doesn't work on RT either. force_sig_info() takes task->sighand->siglock, >>>> which is a 'sleeping' spinlock on RT. >>> >>> Ah, I missed that :/ >>> >>>> Why would we need to disable preemption here at all? What's the problem of >>>> being preempted or even migrated? >>> >>> There *might* not be a problem, I'm just really nervous about changing >>> the behaviour on the debug path and subtly changing how ptrace behaves. >>> >>> My worry was that you could somehow get back into the tracer, and it >>> could remove a software breakpoint in the knowledge that it wouldn't >>> see any future (spurious) SIGTRAPs for that location. >>> >>> Without a concrete example, however, I guess I'll bite the bullet and >>> enable irqs across the call to force_sig_info, since there is clearly a >>> real issue here on RT. >> >> This might be buried in email storm during the holiday. Just want to double >> check the status. I'm supposed there is no objection for getting it merged >> in upstream? > > Sorry, when you replied with: > >> I think we could just extend the "signal delay send" approach from x86-64 >> to arm64, which is currently used by x86-64 on -rt kernel only. > > I understood that you were going to fix -rt, so I dropped this pending > anything more from you. > > What's the plan? Sorry for the confusion. The "signal delay send" approach used by x86-64 -rt should be not necessary for arm64 right now. Reenabling interrupt is still the preferred approach. Since x86-64 has per-CPU IST exception stack, so preemption has to be disabled all the time. However, it is not applicable to other architectures for now, including arm64. Thanks, Yang > > Will >