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=-16.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=ham 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 ABA06C07E95 for ; Wed, 7 Jul 2021 16:33:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8371B61CC8 for ; Wed, 7 Jul 2021 16:33:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230018AbhGGQgZ (ORCPT ); Wed, 7 Jul 2021 12:36:25 -0400 Received: from foss.arm.com ([217.140.110.172]:40622 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229975AbhGGQgY (ORCPT ); Wed, 7 Jul 2021 12:36:24 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 236511042; Wed, 7 Jul 2021 09:33:44 -0700 (PDT) Received: from e113632-lin.cambridge.arm.com (e113632-lin.cambridge.arm.com [10.1.194.46]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id AB1CE3F694; Wed, 7 Jul 2021 09:33:42 -0700 (PDT) From: Valentin Schneider To: linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org Cc: Guenter Roeck , Heiko Carstens , Vasily Gorbik , Christian Borntraeger , Frederic Weisbecker , Alexey Kardashevskiy , Peter Zijlstra , Ingo Molnar Subject: [PATCH] s390: preempt: Fix preempt_count initialization Date: Wed, 7 Jul 2021 17:33:38 +0100 Message-Id: <20210707163338.1623014-1-valentin.schneider@arm.com> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-s390@vger.kernel.org S390's init_idle_preempt_count(p, cpu) doesn't actually let us initialize the preempt_count of the requested CPU's idle task: it unconditionally writes to the current CPU's. This clearly conflicts with idle_threads_init(), which intends to initialize *all* the idle tasks, including their preempt_count (or their CPU's, if the arch uses a per-CPU preempt_count). Unfortunately, it seems the way s390 does things doesn't let us initialize every possible CPU's preempt_count early on, as the pages where this resides are only allocated when a CPU is brought up and are freed when it is brought down. Let the arch-specific code set a CPU's preempt_count when its lowcore is allocated, and turn init_idle_preempt_count() into an empty stub. Fixes: f1a0a376ca0c ("sched/core: Initialize the idle task with preemption disabled") Reported-by: Guenter Roeck Signed-off-by: Valentin Schneider --- arch/s390/include/asm/preempt.h | 16 ++++------------ arch/s390/kernel/setup.c | 1 + arch/s390/kernel/smp.c | 1 + 3 files changed, 6 insertions(+), 12 deletions(-) diff --git a/arch/s390/include/asm/preempt.h b/arch/s390/include/asm/preempt.h index 23ff51be7e29..d9d5350cc3ec 100644 --- a/arch/s390/include/asm/preempt.h +++ b/arch/s390/include/asm/preempt.h @@ -29,12 +29,6 @@ static inline void preempt_count_set(int pc) old, new) != old); } -#define init_task_preempt_count(p) do { } while (0) - -#define init_idle_preempt_count(p, cpu) do { \ - S390_lowcore.preempt_count = PREEMPT_DISABLED; \ -} while (0) - static inline void set_preempt_need_resched(void) { __atomic_and(~PREEMPT_NEED_RESCHED, &S390_lowcore.preempt_count); @@ -88,12 +82,6 @@ static inline void preempt_count_set(int pc) S390_lowcore.preempt_count = pc; } -#define init_task_preempt_count(p) do { } while (0) - -#define init_idle_preempt_count(p, cpu) do { \ - S390_lowcore.preempt_count = PREEMPT_DISABLED; \ -} while (0) - static inline void set_preempt_need_resched(void) { } @@ -130,6 +118,10 @@ static inline bool should_resched(int preempt_offset) #endif /* CONFIG_HAVE_MARCH_Z196_FEATURES */ +#define init_task_preempt_count(p) do { } while (0) +/* Deferred to CPU bringup time */ +#define init_idle_preempt_count(p, cpu) do { } while (0) + #ifdef CONFIG_PREEMPTION extern void preempt_schedule(void); #define __preempt_schedule() preempt_schedule() diff --git a/arch/s390/kernel/setup.c b/arch/s390/kernel/setup.c index 5aab59ad5688..382d73da134c 100644 --- a/arch/s390/kernel/setup.c +++ b/arch/s390/kernel/setup.c @@ -466,6 +466,7 @@ static void __init setup_lowcore_dat_off(void) lc->br_r1_trampoline = 0x07f1; /* br %r1 */ lc->return_lpswe = gen_lpswe(__LC_RETURN_PSW); lc->return_mcck_lpswe = gen_lpswe(__LC_RETURN_MCCK_PSW); + lc->preempt_count = PREEMPT_DISABLED; set_prefix((u32)(unsigned long) lc); lowcore_ptr[0] = lc; diff --git a/arch/s390/kernel/smp.c b/arch/s390/kernel/smp.c index 111909aeb8d2..1fb483e06a64 100644 --- a/arch/s390/kernel/smp.c +++ b/arch/s390/kernel/smp.c @@ -219,6 +219,7 @@ static int pcpu_alloc_lowcore(struct pcpu *pcpu, int cpu) lc->br_r1_trampoline = 0x07f1; /* br %r1 */ lc->return_lpswe = gen_lpswe(__LC_RETURN_PSW); lc->return_mcck_lpswe = gen_lpswe(__LC_RETURN_MCCK_PSW); + lc->preempt_count = PREEMPT_DISABLED; if (nmi_alloc_per_cpu(lc)) goto out_stack; lowcore_ptr[cpu] = lc; -- 2.25.1