From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gu Zheng Subject: Re: [PATCH] driver core / ACPI: Avoid device removal locking problems Date: Wed, 28 Aug 2013 10:12:16 +0800 Message-ID: <521D5C80.7010904@cn.fujitsu.com> References: <1543475.L7gSB7lLAu@vostro.rjw.lan> <4785337.sqQqDSPcpL@vostro.rjw.lan> <3389643.Fdir3g6c6B@vostro.rjw.lan> <1430120.G7JdUKlgj6@vostro.rjw.lan> <521C6FA8.4070804@cn.fujitsu.com> <1377639529.10300.847.camel@misato.fc.hp.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Return-path: Received: from cn.fujitsu.com ([222.73.24.84]:3971 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1752113Ab3H1CQn (ORCPT ); Tue, 27 Aug 2013 22:16:43 -0400 In-Reply-To: <1377639529.10300.847.camel@misato.fc.hp.com> Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: Toshi Kani Cc: "Rafael J. Wysocki" , ACPI Devel Maling List , Greg Kroah-Hartman , LKML , Yasuaki Ishimatsu , Tejun Heo Hi Toshi, On 08/28/2013 05:38 AM, Toshi Kani wrote: > On Tue, 2013-08-27 at 17:21 +0800, Gu Zheng wrote: >> Hi Rafael, >> >> On 08/26/2013 11:02 PM, Rafael J. Wysocki wrote: >> >>> On Monday, August 26, 2013 04:43:26 PM Rafael J. Wysocki wrote: >>>> On Monday, August 26, 2013 02:42:09 PM Rafael J. Wysocki wrote: >>>>> On Monday, August 26, 2013 11:13:13 AM Gu Zheng wrote: >>>>>> Hi Rafael, >>> >>> [...] >>> >>>> >>>> OK, so the patch below is quick and dirty and overkill, but it should make the >>>> splat go away at least. >>> >>> And if this patch does make the splat go away for you, please also test the >>> appended one (Tejun, thanks for the hint!). >>> >>> I'll address the ACPI part differently later. >> >> What about changing device_hotplug_lock and acpi_scan_lock to rwsem? like the >> attached one(With a preliminary test, it also can make the splat go away).:) > > I am curious how msleep(10) & restart_syscall() work in the change > below. Doesn't the msleep() make s_active held longer time, which can > lead the thread holding device_hotplug_lock to wait it for deletion? Yes, but it can avoid busy waiting. > Also, does restart_syscall() release s_active and reopen this file > again? Sure, it just set a TIF_SIGPENDING flag and return an -ERESTARTNOINTR error, s_active/file will be released/closed in the failed path. And when do_signal() catches the -ERESTARTNOINTR, it will change the regs to restart the syscall. Thanks, Gu > > @@ -408,9 +408,13 @@ static ssize_t show_online(struct device *dev, > struct device_attribute *attr, > { > bool val; > > - lock_device_hotplug(); > + if (!read_lock_device_hotplug()) { > + msleep(10); > + return restart_syscall(); > + } > + > > Thanks, > -Toshi > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ >