From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760028Ab1LPDVW (ORCPT ); Thu, 15 Dec 2011 22:21:22 -0500 Received: from db3ehsobe001.messaging.microsoft.com ([213.199.154.139]:49546 "EHLO DB3EHSOBE001.bigfish.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751672Ab1LPDVV (ORCPT ); Thu, 15 Dec 2011 22:21:21 -0500 X-SpamScore: 0 X-BigFish: VPS0(zzzz1202hzz8275bhz2fh668h839h) X-Forefront-Antispam-Report: CIP:160.33.98.74;KIP:(null);UIP:(null);IPV:NLI;H:mail7.fw-bc.sony.com;RD:mail7.fw-bc.sony.com;EFVD:NLI Message-ID: <4EEAB90D.3050504@am.sony.com> Date: Thu, 15 Dec 2011 19:20:45 -0800 From: Frank Rowand Reply-To: User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.17) Gecko/20110428 Fedora/3.1.10-1.fc14 Thunderbird/3.1.10 MIME-Version: 1.0 To: , , , CC: Subject: [PATCH] PREEMPT_RT_FULL: ARM context switch needs IRQs enabled Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit X-OriginatorOrg: am.sony.com Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ARMv6 and later have VIPT caches and the TLBs are tagged with an ASID (application specific ID). The number of ASIDs is limited to 256 and the allocation algorithm requires IPIs when all the ASIDs have been used. The IPIs require interrupts enabled during context switch for deadlock avoidance. The RT patch mm-protect-activate-switch-mm.patch disables irqs around activate_mm() and switch_mm(), which are the portion of the ARMv6 context switch that require interrupts enabled. The solution for the ARMv6 processors could be to _not_ disable irqs. A more conservative solution is to provide the same environment that the scheduler provides, that is preempt_disable(). This is more resilient for possible future changes to the ARM context switch code that is not aware of the RT patches. This patch will conflict slightly with Catalin's patch set to remove __ARCH_WANT_INTERRUPTS_ON_CTXSW, when that is accepted: http://lkml.indiana.edu/hypermail/linux/kernel/1111.3/01893.html When Catalin's patch set is accepted, this RT patch will need to reverse the change in patch 6 to arch/arm/include/asm/system.h: -#ifndef CONFIG_CPU_HAS_ASID -#define __ARCH_WANT_INTERRUPTS_ON_CTXSW -#endif Signed-off-by: Frank Rowand --- fs/exec.c | 8 8 + 0 - 0 ! mm/mmu_context.c | 8 8 + 0 - 0 ! 2 files changed, 16 insertions(+) Index: b/fs/exec.c =================================================================== --- a/fs/exec.c +++ b/fs/exec.c @@ -837,12 +837,20 @@ static int exec_mmap(struct mm_struct *m } } task_lock(tsk); +#ifdef __ARCH_WANT_INTERRUPTS_ON_CTXSW + preempt_disable(); +#else local_irq_disable_rt(); +#endif active_mm = tsk->active_mm; tsk->mm = mm; tsk->active_mm = mm; activate_mm(active_mm, mm); +#ifdef __ARCH_WANT_INTERRUPTS_ON_CTXSW + preempt_enable(); +#else local_irq_enable_rt(); +#endif task_unlock(tsk); arch_pick_mmap_layout(mm); if (old_mm) { Index: b/mm/mmu_context.c =================================================================== --- a/mm/mmu_context.c +++ b/mm/mmu_context.c @@ -26,7 +26,11 @@ void use_mm(struct mm_struct *mm) struct task_struct *tsk = current; task_lock(tsk); +#ifdef __ARCH_WANT_INTERRUPTS_ON_CTXSW + preempt_disable(); +#else local_irq_disable_rt(); +#endif active_mm = tsk->active_mm; if (active_mm != mm) { atomic_inc(&mm->mm_count); @@ -34,7 +38,11 @@ void use_mm(struct mm_struct *mm) } tsk->mm = mm; switch_mm(active_mm, mm, tsk); +#ifdef __ARCH_WANT_INTERRUPTS_ON_CTXSW + preempt_enable(); +#else local_irq_enable_rt(); +#endif task_unlock(tsk); if (active_mm != mm)