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=-13.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 3004EC43387 for ; Tue, 8 Jan 2019 19:41:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id F21212063F for ; Tue, 8 Jan 2019 19:41:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1546976517; bh=0lqQdVI+oKmoAS+QvIsR8GxVuNUJjt4ki3UZiHfiW4A=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=MzhllTeXLq/fJWy9KhM2GS7vWVa1mvrpgvBipzo+QCLGfzxw9RUFgz4niBNn7/sL7 C84wGWkRqjCRmRSWgb5YvV7Zs8MwlRVdg+oSDSqgN/+Mxj1lSwiKOKXeaJdeZPkRwx 8/Gqnzrpevx8qljSFzRR9Vyb5moRxA1cM4L7Z2IM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732627AbfAHTl4 (ORCPT ); Tue, 8 Jan 2019 14:41:56 -0500 Received: from mail.kernel.org ([198.145.29.99]:42952 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731910AbfAHTeN (ORCPT ); Tue, 8 Jan 2019 14:34:13 -0500 Received: from sasha-vm.mshome.net (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id C3A1A2063F; Tue, 8 Jan 2019 19:34:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1546976052; bh=0lqQdVI+oKmoAS+QvIsR8GxVuNUJjt4ki3UZiHfiW4A=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=VrOds13xW1IkslEL+oPWRjLH3KffYwFp6oZ3LW5q0/cu5f6U2Rw/FXKVBOhjzcGAX g1rCY1833ivWpgYlprr87Pwit4CePsHeWoDVyHChhXAr4vOKmLqg8M+ZusGK7P/xzB fJHSprhBDCZk/iVzWn18btUa9KQ+VDQnWGNlBCfc= From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Breno Leitao , Michael Ellerman , Sasha Levin , linux-pm@vger.kernel.org, linuxppc-dev@lists.ozlabs.org Subject: [PATCH AUTOSEL 4.9 15/36] powerpc/pseries/cpuidle: Fix preempt warning Date: Tue, 8 Jan 2019 14:33:27 -0500 Message-Id: <20190108193348.123880-15-sashal@kernel.org> X-Mailer: git-send-email 2.19.1 In-Reply-To: <20190108193348.123880-1-sashal@kernel.org> References: <20190108193348.123880-1-sashal@kernel.org> MIME-Version: 1.0 X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Breno Leitao [ 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