From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CAFDCC433E0 for ; Mon, 8 Mar 2021 18:15:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A567B652B7 for ; Mon, 8 Mar 2021 18:15:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230490AbhCHSPa (ORCPT ); Mon, 8 Mar 2021 13:15:30 -0500 Received: from foss.arm.com ([217.140.110.172]:41854 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230299AbhCHSPA (ORCPT ); Mon, 8 Mar 2021 13:15:00 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 283E8D6E; Mon, 8 Mar 2021 10:15:00 -0800 (PST) Received: from e120325.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id B8C283F71B; Mon, 8 Mar 2021 10:14:58 -0800 (PST) Date: Mon, 8 Mar 2021 18:14:49 +0000 From: Beata Michalska To: Viresh Kumar Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, vireshk@kernel.org, nm@ti.com, sboyd@kernel.org Subject: Re: [PATCH] opp: Invalidate current opp when draining the opp list Message-ID: <20210308181446.GA26783@e120325.cambridge.arm.com> References: <1614870454-18709-1-git-send-email-beata.michalska@arm.com> <20210305042401.gktrgach4dzxp7on@vireshk-i7> <418fc3cb-d5ec-9216-269a-e055e78718e5@arm.com> <20210308115053.ua2gfo6kfnfjslyd@vireshk-i7> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210308115053.ua2gfo6kfnfjslyd@vireshk-i7> User-Agent: Mutt/1.9.4 (2018-02-28) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Mar 08, 2021 at 05:20:53PM +0530, Viresh Kumar wrote: > On 05-03-21, 13:55, Beata Michalska wrote: > > Actually, that one might be problematic: by the time the > > _opp_table_kref_release is being reached, the opp pointed to > > by current_opp may no longer be valid. > > _opp_remove_all_static and/or dev_pm_opp_remove_all_dynamic > > will release all the opps by going through opp_table->opp_list. > > It will drop the reference for each opp on the list, until > > the list gets empty(for given opp type), which means, > > all the opps will actually get released > > (only upon _opp_kref_release the opp will get removed > > from the list). > > Sorry for missing the context completely, I get it now. > > This is what I have applied instead, please see if it breaks anything > or works as expected. > > -------------------------8<------------------------- > > From: Beata Michalska > Date: Thu, 4 Mar 2021 15:07:34 +0000 > Subject: [PATCH] opp: Invalidate current opp when draining the opp list > > The current_opp when set, grabs additional reference on the opp, > which is then supposed to be dropped upon releasing the opp table. > > Still both dev_pm_opp_remove_table and dev_pm_opp_remove_all_dynamic > will completely drain the OPPs list, including dropping the additional > reference on current_opp because they run until the time list gets > empty. > > This will lead releasing the current_opp one more time when the OPP > table gets removed and so will raise ref counting issues. > > Fix that by making sure we don't release the extra reference to the > current_opp. > > Fixes: 81c4d8a3c414 ("opp: Keep track of currently programmed OPP") > Signed-off-by: Beata Michalska > [ Viresh: Rewrite _opp_drain_list() to not drop the extra count instead > of depending on reference counting. Update commit log and > other minor changes. ] > Signed-off-by: Viresh Kumar > --- > drivers/opp/core.c | 52 +++++++++++++++++++++++++++++----------------- > 1 file changed, 33 insertions(+), 19 deletions(-) > > diff --git a/drivers/opp/core.c b/drivers/opp/core.c > index c2689386a906..3cc0a1b82adc 100644 > --- a/drivers/opp/core.c > +++ b/drivers/opp/core.c > @@ -1502,10 +1502,38 @@ static struct dev_pm_opp *_opp_get_next(struct opp_table *opp_table, > return opp; > } > > -bool _opp_remove_all_static(struct opp_table *opp_table) > +/* > + * Can't remove the OPP from under the lock, debugfs removal needs to happen > + * lock less to avoid circular dependency issues. This must be called without > + * the opp_table->lock held. > + */ > +static int _opp_drain_list(struct opp_table *opp_table, bool dynamic) > { > - struct dev_pm_opp *opp; > + struct dev_pm_opp *opp, *current_opp = NULL; > + int count = 0; > + > + while ((opp = _opp_get_next(opp_table, dynamic))) { > + if (opp_table->current_opp == opp) { > + /* > + * Reached at current OPP twice, no other OPPs left. The > + * last reference to current_opp is dropped from > + * _opp_table_kref_release(). > + */ > + if (current_opp) > + break; > + > + current_opp = opp; > + } Having a quick look at the code ... Shouldn't the current_opp be moved at the end of the list ? Otherwise there is a risk of leaving unreferenced opps (and opp_table). Might be also worth adding warning (?) WARN_ONCE(!list_is_singular()) --- BR B. > + > + dev_pm_opp_put(opp); > + count++; > + } > + > + return count; > +} > > +bool _opp_remove_all_static(struct opp_table *opp_table) > +{ > mutex_lock(&opp_table->lock); > > if (!opp_table->parsed_static_opps) { > @@ -1520,13 +1548,7 @@ bool _opp_remove_all_static(struct opp_table *opp_table) > > mutex_unlock(&opp_table->lock); > > - /* > - * Can't remove the OPP from under the lock, debugfs removal needs to > - * happen lock less to avoid circular dependency issues. > - */ > - while ((opp = _opp_get_next(opp_table, false))) > - dev_pm_opp_put(opp); > - > + _opp_drain_list(opp_table, false); > return true; > } > > @@ -1539,21 +1561,13 @@ bool _opp_remove_all_static(struct opp_table *opp_table) > void dev_pm_opp_remove_all_dynamic(struct device *dev) > { > struct opp_table *opp_table; > - struct dev_pm_opp *opp; > - int count = 0; > + int count; > > opp_table = _find_opp_table(dev); > if (IS_ERR(opp_table)) > return; > > - /* > - * Can't remove the OPP from under the lock, debugfs removal needs to > - * happen lock less to avoid circular dependency issues. > - */ > - while ((opp = _opp_get_next(opp_table, true))) { > - dev_pm_opp_put(opp); > - count++; > - } > + count = _opp_drain_list(opp_table, true); > > /* Drop the references taken by dev_pm_opp_add() */ > while (count--)