From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757488AbaHGJds (ORCPT ); Thu, 7 Aug 2014 05:33:48 -0400 Received: from mga09.intel.com ([134.134.136.24]:29714 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757382AbaHGJdp (ORCPT ); Thu, 7 Aug 2014 05:33:45 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.01,816,1400050800"; d="scan'208";a="584660896" Message-ID: <53E3475A.9090301@intel.com> Date: Thu, 07 Aug 2014 17:31:06 +0800 From: Lan Tianyu User-Agent: Mozilla/5.0 (X11; Linux i686 on x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.0 MIME-Version: 1.0 To: "Rafael J. Wysocki" CC: lenb@kernel.org, linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] ACPI/OSL: Remove RCU in the osl.c to avoid dead lock with cpu hot plug References: <1407141608-28920-1-git-send-email-tianyu.lan@intel.com> <1655155.Bsn9BIJnyn@vostro.rjw.lan> <53E19175.208@intel.com> <5565710.HfsfjXfcL3@vostro.rjw.lan> In-Reply-To: <5565710.HfsfjXfcL3@vostro.rjw.lan> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2014年08月07日 03:09, Rafael J. Wysocki wrote: > On Wednesday, August 06, 2014 10:22:45 AM Lan Tianyu wrote: >> On 2014年08月06日 09:24, Rafael J. Wysocki wrote: >>> On Monday, August 04, 2014 04:40:08 PM Lan Tianyu wrote: > > [cut] > >>>> @@ -298,29 +298,29 @@ void __iomem *acpi_os_get_iomem(acpi_physical_address phys, unsigned int size) >>>> { >>>> struct acpi_ioremap *map; >>>> void __iomem *virt = NULL; >>>> + unsigned long flags; >>>> >>>> - mutex_lock(&acpi_ioremap_lock); >>>> + spin_lock_irqsave(&acpi_ioremap_lock, flags); >>> >>> Why do you need to do _irqsave here? It was a mutex before, after all, >>> so it can't be called from interrupt context. >>> >>> In other places below too. >> >> Original code uses RCU lock to protect acpi_ioremaps list in the >> acpi_os_read/write_memory() which will be called in apei_read/write(). >> apei_read/write() will be called in the interrupt from APEI comments. > > But acpi_os_get_iomem() won't be called from interrupt context and should use > spin_lock_irq() instead of _irqsave. This also applies to the other places > that use the mutex. Yes, that's correct. Sorry. I misunderstood what you meant. > >> Now replace RCU with acpi_ioremap_lock and the lock will be called in >> the interrupt. So redefine it to spin lock. From history, >> acpi_ioremap_lock was spin lock before adding RCU support. > > And it had scalability problems IIRC. > > Did you consider using SRCU instead of going back to the spinlock? No, I will have a look at SRCU. > > Rafael > -- Best regards Tianyu Lan