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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id BE59EC433EF for ; Mon, 25 Oct 2021 19:35:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A751C60FE8 for ; Mon, 25 Oct 2021 19:35:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235263AbhJYThX (ORCPT ); Mon, 25 Oct 2021 15:37:23 -0400 Received: from mail.kernel.org ([198.145.29.99]:53596 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236399AbhJYTef (ORCPT ); Mon, 25 Oct 2021 15:34:35 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 9A88F6109D; Mon, 25 Oct 2021 19:30:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1635190227; bh=l+aJgEfVuDl8zzpogCNlpLYbkm6U/2dZP1qpAopXYrA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=iSKNNvVgepXZktQsoujKPyBTjPCQr8hbhFTI1CCBIi+WedGUNhkgbqsfDcadg1mf4 8MOHoJzHVwlef8T7U4x5hajQW3VN+fbqLJaLS6vr1vGmdY+u/Vqcrl+YlrCWeuKkw7 WDJLabCj0igoreNryzzybTYM2ajOFitLvPoEMrQA= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Nathan Lynch , Valentin Schneider , Srikar Dronamraju , Michael Ellerman , Sasha Levin Subject: [PATCH 5.10 23/95] powerpc/smp: do not decrement idle task preempt count in CPU offline Date: Mon, 25 Oct 2021 21:14:20 +0200 Message-Id: <20211025191000.277041864@linuxfoundation.org> X-Mailer: git-send-email 2.33.1 In-Reply-To: <20211025190956.374447057@linuxfoundation.org> References: <20211025190956.374447057@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Nathan Lynch [ Upstream commit 787252a10d9422f3058df9a4821f389e5326c440 ] With PREEMPT_COUNT=y, when a CPU is offlined and then onlined again, we get: BUG: scheduling while atomic: swapper/1/0/0x00000000 no locks held by swapper/1/0. CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.15.0-rc2+ #100 Call Trace: dump_stack_lvl+0xac/0x108 __schedule_bug+0xac/0xe0 __schedule+0xcf8/0x10d0 schedule_idle+0x3c/0x70 do_idle+0x2d8/0x4a0 cpu_startup_entry+0x38/0x40 start_secondary+0x2ec/0x3a0 start_secondary_prolog+0x10/0x14 This is because powerpc's arch_cpu_idle_dead() decrements the idle task's preempt count, for reasons explained in commit a7c2bb8279d2 ("powerpc: Re-enable preemption before cpu_die()"), specifically "start_secondary() expects a preempt_count() of 0." However, since commit 2c669ef6979c ("powerpc/preempt: Don't touch the idle task's preempt_count during hotplug") and commit f1a0a376ca0c ("sched/core: Initialize the idle task with preemption disabled"), that justification no longer holds. The idle task isn't supposed to re-enable preemption, so remove the vestigial preempt_enable() from the CPU offline path. Tested with pseries and powernv in qemu, and pseries on PowerVM. Fixes: 2c669ef6979c ("powerpc/preempt: Don't touch the idle task's preempt_count during hotplug") Signed-off-by: Nathan Lynch Reviewed-by: Valentin Schneider Reviewed-by: Srikar Dronamraju Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20211015173902.2278118-1-nathanl@linux.ibm.com Signed-off-by: Sasha Levin --- arch/powerpc/kernel/smp.c | 2 -- 1 file changed, 2 deletions(-) diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c index 91f274134884..452cbf98bfd7 100644 --- a/arch/powerpc/kernel/smp.c +++ b/arch/powerpc/kernel/smp.c @@ -1578,8 +1578,6 @@ void __cpu_die(unsigned int cpu) void arch_cpu_idle_dead(void) { - sched_preempt_enable_no_resched(); - /* * Disable on the down path. This will be re-enabled by * start_secondary() via start_secondary_resume() below -- 2.33.0