From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Authentication-Results: smtp.codeaurora.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="PVEJVB1f" DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org A43CA605BD Authentication-Results: pdx-caf-mail.web.codeaurora.org; dmarc=none (p=none dis=none) header.from=linuxfoundation.org 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 S932472AbeFFIYt (ORCPT + 25 others); Wed, 6 Jun 2018 04:24:49 -0400 Received: from mail.kernel.org ([198.145.29.99]:43898 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932329AbeFFIYs (ORCPT ); Wed, 6 Jun 2018 04:24:48 -0400 Date: Wed, 6 Jun 2018 10:24:22 +0200 From: Greg Kroah-Hartman To: Kim Phillips Cc: Mathieu Poirier , Leo Yan , Suzuki K Poulose , 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 Subject: Re: [PATCH v4 05/14] coresight: get/put module in coresight_build/release_path Message-ID: <20180606082422.GB19727@kroah.com> References: <20180605210710.22227-1-kim.phillips@arm.com> <20180605210710.22227-6-kim.phillips@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180605210710.22227-6-kim.phillips@arm.com> User-Agent: Mutt/1.10.0 (2018-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. thanks, greg k-h