From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.9 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9E4ADC433DF for ; Mon, 6 Jul 2020 16:50:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7A5D820702 for ; Mon, 6 Jul 2020 16:50:09 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="bPNiRKeL"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="c4xPTn9L" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729589AbgGFQuI (ORCPT ); Mon, 6 Jul 2020 12:50:08 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49582 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729384AbgGFQuI (ORCPT ); Mon, 6 Jul 2020 12:50:08 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CCD4BC061755; Mon, 6 Jul 2020 09:50:07 -0700 (PDT) Date: Mon, 6 Jul 2020 18:50:04 +0200 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1594054205; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=/CG85fqqBbn5eKIZULRuWM7oiLGrENgTSZkiqJx1JRc=; b=bPNiRKeLIGvE8XKMEf8oZ43m+VsPJvzu9BiCFSKpc6xeN5SnXGSULqnLBIBXdemQPbhLys 7lHqedX6PThJWhiWgJ9VGhARkhQUVqovF6Bj7QCuyfkxcZO/p+dKoNo5clh//Du2EtiL+k DKk+kQIVdT6kXBHIqRTEUeN2REQIaQPJSbSueD7M/hrOzn1cMVEBI0wkgUbeVo17JPYKu0 T0A83/k40MKcfk+ar3QZuKUxqboGGlDl1/hoBmtu5JhLslXb9lk8Z2DEBAGQP6+Lb+a7nJ AWns6Mk0ZFqCHc+JDu1kDRxZjMiz3S3olUtq1mCun5q7tmAx4Y7kz2222GFzMg== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1594054205; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=/CG85fqqBbn5eKIZULRuWM7oiLGrENgTSZkiqJx1JRc=; b=c4xPTn9LMmcAP797YCJuIxpK8xu+wzQYi5kwM7U6LPDbnmcXT9VY3Qq/FRO5YiYi0GAU47 QAP2Tdbqwr9dvECg== From: Sebastian Andrzej Siewior To: Mark Marshall Cc: linux-rt-users , Mark Marshall , thomas.graziadei@omicronenergy.com, Thomas Gleixner , linux-kernel@vger.kernel.org, rostedt@goodmis.org Subject: Re: Kernel crash due to memory corruption with v5.4.26-rt17 and PowerPC e500 Message-ID: <20200706165004.7m57fvspmwnjcjxh@linutronix.de> References: <20200529131452.pgj7mx7xaz7n4kz3@linutronix.de> <20200529161518.svpxhkeljafbtdz2@linutronix.de> <20200529163722.mdxzrj4n3lyzjtfu@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable In-Reply-To: <20200529163722.mdxzrj4n3lyzjtfu@linutronix.de> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020-05-29 18:37:22 [+0200], To Mark Marshall wrote: > On 2020-05-29 18:15:18 [+0200], To Mark Marshall wrote: > > In order to get it back into the RT queue I need to understand why it is > > required. What exactly is it fixing. Let me stare at for a little=E2=80= =A6 >=20 > it used to be local_irq_disable() which then became preempt_disable() > local_irq_disable() due to ARM's limitation. Any luck on your side? I *think* if you swap the mm assignment in exec_mmap() then it should be gone. Basically: | tsk->active_mm =3D mm; | tsk->mm =3D mm; However I think to apply something like this: diff --git a/fs/exec.c b/fs/exec.c --- a/fs/exec.c +++ b/fs/exec.c @@ -1035,11 +1035,15 @@ static int exec_mmap(struct mm_struct *mm) } } task_lock(tsk); + + task_lock_mm(); active_mm =3D tsk->active_mm; membarrier_exec_mmap(mm); tsk->mm =3D mm; tsk->active_mm =3D mm; activate_mm(active_mm, mm); + task_unlock_mm(); + tsk->mm->vmacache_seqnum =3D 0; vmacache_flush(tsk); task_unlock(tsk); diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h --- a/include/linux/sched/task.h +++ b/include/linux/sched/task.h @@ -176,4 +176,31 @@ static inline void task_unlock(struct task_struct *p) spin_unlock(&p->alloc_lock); } =20 +#ifdef CONFIG_PREEMPT_RT +/* + * Protects ->mm and ->active_mm. + * Avoids scheduling so switch_mm() or enter_lazy_tlb() will not read the + * members while they are updated. + */ +static inline void task_lock_mm(void) +{ + preempt_disable(); +} + +static inline void task_unlock_mm(void) +{ + preempt_enable(); +} + +#else + +static inline void task_lock_mm(void) +{ +} + +static inline void task_unlock_mm(void) +{ +} +#endif + #endif /* _LINUX_SCHED_TASK_H */ diff --git a/mm/mmu_context.c b/mm/mmu_context.c --- a/mm/mmu_context.c +++ b/mm/mmu_context.c @@ -25,6 +25,7 @@ void use_mm(struct mm_struct *mm) struct task_struct *tsk =3D current; =20 task_lock(tsk); + task_lock_mm(); active_mm =3D tsk->active_mm; if (active_mm !=3D mm) { mmgrab(mm); @@ -32,6 +33,7 @@ void use_mm(struct mm_struct *mm) } tsk->mm =3D mm; switch_mm(active_mm, mm, tsk); + task_unlock_mm(); task_unlock(tsk); #ifdef finish_arch_post_lock_switch finish_arch_post_lock_switch(); @@ -55,10 +57,12 @@ void unuse_mm(struct mm_struct *mm) struct task_struct *tsk =3D current; =20 task_lock(tsk); + task_lock_mm(); sync_mm_rss(mm); tsk->mm =3D NULL; /* active_mm is still 'mm' */ enter_lazy_tlb(mm, tsk); + task_unlock_mm(); task_unlock(tsk); } EXPORT_SYMBOL_GPL(unuse_mm); --=20 2.27.0 > > > Best regards, > > > Mark Sebastian