From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Shi, Yang" Subject: Re: [PATCH v2] rt: x86: enable preemption in IST exception for x86-32 Date: Tue, 22 Dec 2015 10:12:42 -0800 Message-ID: <5679929A.5030806@linaro.org> References: <1450134404-16662-1-git-send-email-yang.shi@linaro.org> <20151222120628.GA27274@linutronix.de> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Cc: tglx@linutronix.de, rostedt@goodmis.org, linux-kernel@vger.kernel.org, linux-rt-users@vger.kernel.org, linaro-kernel@lists.linaro.org To: Sebastian Andrzej Siewior Return-path: Received: from mail-pa0-f48.google.com ([209.85.220.48]:34771 "EHLO mail-pa0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754130AbbLVSMr (ORCPT ); Tue, 22 Dec 2015 13:12:47 -0500 Received: by mail-pa0-f48.google.com with SMTP id uo6so15707436pac.1 for ; Tue, 22 Dec 2015 10:12:47 -0800 (PST) In-Reply-To: <20151222120628.GA27274@linutronix.de> Sender: linux-rt-users-owner@vger.kernel.org List-ID: On 12/22/2015 4:06 AM, Sebastian Andrzej Siewior wrote: > * Yang Shi | 2015-12-14 15:06:44 [-0800]: > >> Mainline kernel commit 959274753857efe9c5f1ba35fe727f51e9aa128d >> ("x86, traps: Track entry into and exit from IST context"), introduced >> ist_enter which disables preemption uncondiontionally for both x86-64 and >> x86-32. However, x86-32 does not have an IST and the stack still belongs to >> the current task and there is no problem in scheduling out the task. > > no no. So from a quick look I *assumed* you merged your v1 and revert of the > Steven's patch into one piece. But now I see that you don't disable preemption > 64bit which means you revert upstream change. No, I neither merged my v1 patch nor reverted Steven's patch. Directed by Thomas's suggestion in v1 patch review, I looked into the code further. Currently, the code does: ist_enter disables preemption unconditionally for both x86-64 and x86-32 (by mainline commit). So, for the x86-64 part, it is fine since the preemption should be disabled because ist exception will use per CPU stack and signal delay send is necessary. But, disabling preemption on x86-32 is unnecessary since it doesn't have ist stacks, so the v2 patch re-enables preemption for x86-32. upstream commit 959274753857efe9c5f1ba35fe727f51e9aa128d ("x86, traps: Track entry into and exit from IST context") commit log has more details for the ist stacks. So, #1) v1 patch is not needed anymore since x86-32 still doesn't need signal delay send in v2, #2) don't need revert Steven's patch, the logic is just changed slightly (#ifdef CONFIG_X86_64 --> #if !defined(CONFIG_X86_64)) and adopted the mainline APIs. So, this is definitely a new approach for fixing the same problem and *not* an incremental patch. > > Here is what happens: > - I drop your v2 > - I merge your v1 with updated patch description > - I revert "x86: Do not disable preemption in int3 on 32bit". If someone > wants to skip the delayed signal on 32bit please address this upstream > first (that is skip the preempt_disable() on 32bit if it is not > required there). > - Yang Shi, please send a changelong if you send incremental patches. Sorry for any inconvenience. I should made the comment clearer at the first place even though it is not an incremental patch. Thanks, Yang > > Sebastian >