From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org 4A8366070B Authentication-Results: pdx-caf-mail.web.codeaurora.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: pdx-caf-mail.web.codeaurora.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932291AbeFFJqj (ORCPT + 25 others); Wed, 6 Jun 2018 05:46:39 -0400 Received: from foss.arm.com ([217.140.101.70]:38618 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750794AbeFFJqi (ORCPT ); Wed, 6 Jun 2018 05:46:38 -0400 Subject: Re: [PATCH v4 05/14] coresight: get/put module in coresight_build/release_path To: Greg Kroah-Hartman , Kim Phillips Cc: Mathieu Poirier , Leo Yan , Alexander Shishkin , Alex Williamson , Andrew Morton , David Howells , Eric Auger , Eric Biederman , Gargi Sharma , Geert Uytterhoeven , Kefeng Wang , Kirill Tkhai , Mike Rapoport , Oleg Nesterov , Pavel Tatashin , Rik van Riel , Robin Murphy , Russell King , Thierry Reding , Todd Kjos , Randy Dunlap , linux-arm-kernel , Linux Kernel Mailing List References: <20180605210710.22227-1-kim.phillips@arm.com> <20180605210710.22227-6-kim.phillips@arm.com> <20180606082422.GB19727@kroah.com> From: Suzuki K Poulose Message-ID: Date: Wed, 6 Jun 2018 10:46:36 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <20180606082422.GB19727@kroah.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/06/2018 09:24 AM, Greg Kroah-Hartman wrote: > On Tue, Jun 05, 2018 at 04:07:01PM -0500, Kim Phillips wrote: >> Increment the refcnt for driver modules in current use by calling >> module_get in coresight_build_path and module_put in release_path. >> >> This prevents driver modules from being unloaded when they are in use, >> either in sysfs or perf mode. > > Why does it matter? Shouldn't you be allowed to remove any module at > any point in time, much like a networking driver? > > >> >> Cc: Mathieu Poirier >> Cc: Leo Yan >> Cc: Alexander Shishkin >> Cc: Randy Dunlap >> Cc: Suzuki K Poulose >> Cc: Greg Kroah-Hartman >> Cc: Russell King >> Signed-off-by: Kim Phillips >> --- >> drivers/hwtracing/coresight/coresight.c | 9 +++++++++ >> 1 file changed, 9 insertions(+) >> >> diff --git a/drivers/hwtracing/coresight/coresight.c b/drivers/hwtracing/coresight/coresight.c >> index 338f1719641c..1c941351f1d1 100644 >> --- a/drivers/hwtracing/coresight/coresight.c >> +++ b/drivers/hwtracing/coresight/coresight.c >> @@ -465,6 +465,12 @@ static int _coresight_build_path(struct coresight_device *csdev, >> >> node->csdev = csdev; >> list_add(&node->link, path); >> + >> + if (!try_module_get(csdev->dev.parent->driver->owner)) { > > What is to keep parent->driver from going away right here? What keeps > parent around? This feels very fragile to me, I don't see any locking > anywhere around this code path to try to keep things in place. You're right. We do have coresight_mutex, which is held across the build path and the csdev is removed when a device is unregistered. However, I see that we don't hold the mutex while removing the connections from coresight_unregister(). Holding the mutex should protect us from the csdev being removed, while we build the path. And while we are at this, I also realised that we hold references to the parent devices for each connection (via bus_find_device() from of_coresight_get_endpoint_device()), while parsing the platform data, which is never released. Thanks Suzuki > > thanks, > > greg k-h >