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=-10.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,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 47542C282C3 for ; Thu, 24 Jan 2019 20:08:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 164D821855 for ; Thu, 24 Jan 2019 20:08:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1548360488; bh=rDs9l5ssH2pGydvufS4Ma9cbq04rWlbkyROqpQyHJ5g=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=HXik/BT3r99GHZ8bT6RINspb/RNeo3ugRpFLtx3vfnz09SGoJeUxKPf7grxGOLaXd 0Ger4EyFmBhyazatbRVIuMVjxuK7z55vT5TWZ072+Er5jqUg4RrGpIs9lCHRQO0ZCy lzFSk1cqJH/pvwvz4O4oDUBYEWfEeoROtdM8kabc= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731182AbfAXT31 (ORCPT ); Thu, 24 Jan 2019 14:29:27 -0500 Received: from mail.kernel.org ([198.145.29.99]:56570 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731164AbfAXT3Y (ORCPT ); Thu, 24 Jan 2019 14:29:24 -0500 Received: from localhost (5356596B.cm-6-7b.dynamic.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id BD4A221902; Thu, 24 Jan 2019 19:29:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1548358163; bh=rDs9l5ssH2pGydvufS4Ma9cbq04rWlbkyROqpQyHJ5g=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=SdaUSCjfnocuKGvmi7+0WJVg3DcQSWb2R32h7TG86VZNO5F7sewAf4/xK5qLLBpMO HMEntmVPlWNkmdTGWtOzhlkaJSO1jpmeckkV9c5+No5TmITUXpDt58Gk23QvPFPByS nKFApb3TUmE95ikINAa2u+S1rGmPpXWvI5vQxf8M= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Breno Leitao , Michael Ellerman , Sasha Levin Subject: [PATCH 4.9 16/39] powerpc/pseries/cpuidle: Fix preempt warning Date: Thu, 24 Jan 2019 20:20:19 +0100 Message-Id: <20190124190448.812351589@linuxfoundation.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190124190448.232316246@linuxfoundation.org> References: <20190124190448.232316246@linuxfoundation.org> User-Agent: quilt/0.65 X-stable: review X-Patchwork-Hint: ignore MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 4.9-stable review patch. If anyone has any objections, please let me know. ------------------ [ Upstream commit 2b038cbc5fcf12a7ee1cc9bfd5da1e46dacdee87 ] When booting a pseries kernel with PREEMPT enabled, it dumps the following warning: BUG: using smp_processor_id() in preemptible [00000000] code: swapper/0/1 caller is pseries_processor_idle_init+0x5c/0x22c CPU: 13 PID: 1 Comm: swapper/0 Not tainted 4.20.0-rc3-00090-g12201a0128bc-dirty #828 Call Trace: [c000000429437ab0] [c0000000009c8878] dump_stack+0xec/0x164 (unreliable) [c000000429437b00] [c0000000005f2f24] check_preemption_disabled+0x154/0x160 [c000000429437b90] [c000000000cab8e8] pseries_processor_idle_init+0x5c/0x22c [c000000429437c10] [c000000000010ed4] do_one_initcall+0x64/0x300 [c000000429437ce0] [c000000000c54500] kernel_init_freeable+0x3f0/0x500 [c000000429437db0] [c0000000000112dc] kernel_init+0x2c/0x160 [c000000429437e20] [c00000000000c1d0] ret_from_kernel_thread+0x5c/0x6c This happens because the code calls get_lppaca() which calls get_paca() and it checks if preemption is disabled through check_preemption_disabled(). Preemption should be disabled because the per CPU variable may make no sense if there is a preemption (and a CPU switch) after it reads the per CPU data and when it is used. In this device driver specifically, it is not a problem, because this code just needs to have access to one lppaca struct, and it does not matter if it is the current per CPU lppaca struct or not (i.e. when there is a preemption and a CPU migration). That said, the most appropriate fix seems to be related to avoiding the debug_smp_processor_id() call at get_paca(), instead of calling preempt_disable() before get_paca(). Signed-off-by: Breno Leitao Signed-off-by: Michael Ellerman Signed-off-by: Sasha Levin --- drivers/cpuidle/cpuidle-pseries.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/drivers/cpuidle/cpuidle-pseries.c b/drivers/cpuidle/cpuidle-pseries.c index 166ccd711ec9..83203c59bf59 100644 --- a/drivers/cpuidle/cpuidle-pseries.c +++ b/drivers/cpuidle/cpuidle-pseries.c @@ -230,7 +230,13 @@ static int pseries_idle_probe(void) return -ENODEV; if (firmware_has_feature(FW_FEATURE_SPLPAR)) { - if (lppaca_shared_proc(get_lppaca())) { + /* + * Use local_paca instead of get_lppaca() since + * preemption is not disabled, and it is not required in + * fact, since lppaca_ptr does not need to be the value + * associated to the current CPU, it can be from any CPU. + */ + if (lppaca_shared_proc(local_paca->lppaca_ptr)) { cpuidle_state_table = shared_states; max_idle_state = ARRAY_SIZE(shared_states); } else { -- 2.19.1