From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933630AbaD3J6J (ORCPT ); Wed, 30 Apr 2014 05:58:09 -0400 Received: from us01smtprelay-2.synopsys.com ([198.182.44.111]:46652 "EHLO smtprelay.synopsys.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932198AbaD3J6G (ORCPT ); Wed, 30 Apr 2014 05:58:06 -0400 From: Vineet Gupta To: Linus Torvalds CC: lkml , , Vineet Gupta , , Anton Kolesov , Francois Bedard Subject: [PATCH] ARC: !PREEMPT: Ensure Return to kernel mode is IRQ safe Date: Wed, 30 Apr 2014 15:26:45 +0530 Message-ID: <1398851805-10147-1-git-send-email-vgupta@synopsys.com> X-Mailer: git-send-email 1.8.3.2 MIME-Version: 1.0 Content-Type: text/plain X-Originating-IP: [10.12.196.93] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org There was a very small race window where resume to kernel mode from a Exception Path (or pure kernel mode which is true for most of ARC exceptions anyways), was not disabling interrupts in restore_regs, clobbering the exception regs Anton found the culprit call flow (after many sleepless nights) | 1. we got a Trap from user land | 2. started to service it. | 3. While doing some stuff on user-land memory (I think it is padzero()), | we got a DataTlbMiss | 4. On return from it we are taking "resume_kernel_mode" path | 5. NEED_RESHED is not set, so we go to "return from exception" path in | restore regs. | 6. there seems to be IRQ happening Signed-off-by: Vineet Gupta Cc: #3.10, 3.12, 3.13, 3.14 Cc: Anton Kolesov Cc: Francois Bedard --- arch/arc/kernel/entry.S | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/arch/arc/kernel/entry.S b/arch/arc/kernel/entry.S index 819dd5f7eb05..29b82adbf0b4 100644 --- a/arch/arc/kernel/entry.S +++ b/arch/arc/kernel/entry.S @@ -614,11 +614,13 @@ resume_user_mode_begin: resume_kernel_mode: -#ifdef CONFIG_PREEMPT - - ; This is a must for preempt_schedule_irq() + ; Disable Interrupts from this point on + ; CONFIG_PREEMPT: This is a must for preempt_schedule_irq() + ; !CONFIG_PREEMPT: To ensure restore_regs is intr safe IRQ_DISABLE r9 +#ifdef CONFIG_PREEMPT + ; Can't preempt if preemption disabled GET_CURR_THR_INFO_FROM_SP r10 ld r8, [r10, THREAD_INFO_PREEMPT_COUNT] -- 1.8.3.2