From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752982AbcEMNvX (ORCPT ); Fri, 13 May 2016 09:51:23 -0400 Received: from bh-25.webhostbox.net ([208.91.199.152]:53112 "EHLO bh-25.webhostbox.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751104AbcEMNvW (ORCPT ); Fri, 13 May 2016 09:51:22 -0400 Subject: Re: [PATCH] ARM: hide finish_arch_post_lock_switch from modules To: Arnd Bergmann , Ingo Molnar References: <1463146234-161304-1-git-send-email-arnd@arndb.de> Cc: Andy Lutomirski , Steven Rostedt , Russell King - ARM Linux , Ard Biesheuvel , Peter Zijlstra , Frederic Weisbecker , linux-kernel@vger.kernel.org, Andy Lutomirski , Thomas Gleixner , Borislav Petkov , Mel Gorman , linux-arm-kernel@lists.infradead.org From: Guenter Roeck Message-ID: <5735DBC9.10204@roeck-us.net> Date: Fri, 13 May 2016 06:51:05 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.7.2 MIME-Version: 1.0 In-Reply-To: <1463146234-161304-1-git-send-email-arnd@arndb.de> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-Authenticated_sender: linux@roeck-us.net X-OutGoing-Spam-Status: No, score=-1.0 X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - bh-25.webhostbox.net X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - roeck-us.net X-Get-Message-Sender-Via: bh-25.webhostbox.net: authenticated_id: linux@roeck-us.net X-Authenticated-Sender: bh-25.webhostbox.net: linux@roeck-us.net X-Source: X-Source-Args: X-Source-Dir: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/13/2016 06:30 AM, Arnd Bergmann wrote: > From: Steven Rostedt > > The introduction of switch_mm_irqs_off() brought back an old bug > regarding the use of preempt_enable_no_resched: > > As part of 62b94a08da1b ("sched/preempt: Take away > preempt_enable_no_resched() from modules"), the definition of > preempt_enable_no_resched() is only available in built-in code, > not in loadable modules, so we can't generally use it from header > files. However, the ARM version of finish_arch_post_lock_switch() > calls preempt_enable_no_resched() and is defined as a static > inline function in asm/mmu_context.h. This in turn means we cannot > include asm/mmu_context.h from modules. > > With today's tip tree, asm/mmu_context.h gets included from > linux/mmu_context.h, which is normally the exact pattern one would > expect, but unfortunately, linux/mmu_context.h can be included from > the vhost driver that is a loadable module, now causing this compile > time error: > > In file included from ../include/linux/mmu_context.h:4:0, > from ../drivers/vhost/vhost.c:18: > ../arch/arm/include/asm/mmu_context.h: In function 'finish_arch_post_lock_switch': > ../arch/arm/include/asm/mmu_context.h:88:3: error: implicit declaration of function 'preempt_enable_no_resched' [-Werror=implicit-function-declaration] > preempt_enable_no_resched(); > > Andy already tried to fix the bug by including linux/preempt.h > from asm/mmu_context.h, but that didn't help. I suggested reordering > the header files, which wasn't popular, but Steve came up with this > workaround instead: > > The finish_arch_post_lock_switch() definition is now also hidden > inside of #ifdef MODULE, so we don't see anything referencing > preempt_enable_no_resched() from a header file. I've built a > few hundred randconfig kernels with this, and did not see any > new problems. > > Fixes: f98db6013c55 ("sched/core: Add switch_mm_irqs_off() and use it in the scheduler") > Signed-off-by: Steven Rostedt > Signed-off-by: Arnd Bergmann > Acked-by: Russell King Tested-by: Guenter Roeck > --- > arch/arm/include/asm/mmu_context.h | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/arch/arm/include/asm/mmu_context.h b/arch/arm/include/asm/mmu_context.h > index ed73babc0dc9..3cc14dd8587c 100644 > --- a/arch/arm/include/asm/mmu_context.h > +++ b/arch/arm/include/asm/mmu_context.h > @@ -67,6 +67,7 @@ static inline void check_and_switch_context(struct mm_struct *mm, > cpu_switch_mm(mm->pgd, mm); > } > > +#ifndef MODULE > #define finish_arch_post_lock_switch \ > finish_arch_post_lock_switch > static inline void finish_arch_post_lock_switch(void) > @@ -88,6 +89,7 @@ static inline void finish_arch_post_lock_switch(void) > preempt_enable_no_resched(); > } > } > +#endif /* !MODULE */ > > #endif /* CONFIG_MMU */ > >