From mboxrd@z Thu Jan 1 00:00:00 1970 From: Akhil P Oommen Subject: Re: [PATCH v3] PM / devfreq: Fix devfreq_add_device() when drivers are built as modules. Date: Fri, 22 Jun 2018 14:36:31 +0530 Message-ID: <9ecb2d61-5713-c0dc-9d35-2c926372fd03@codeaurora.org> References: <20180621220430.25644-1-enric.balletbo@collabora.com> <0383b4a703a0b619023c0654a4a7637419c72ebd.camel@collabora.com> <36c9720c-7428-0a17-5252-7afbd80bce6b@collabora.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <36c9720c-7428-0a17-5252-7afbd80bce6b@collabora.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Enric Balletbo i Serra , Ezequiel Garcia , linux-kernel@vger.kernel.org Cc: kernel@collabora.com, Chanwoo Choi , Kyungmin Park , MyungJoo Ham , linux-pm@vger.kernel.org List-Id: linux-pm@vger.kernel.org On 6/22/2018 1:52 PM, Enric Balletbo i Serra wrote: > Hi Ezequiel and Akhil, > > On 22/06/18 09:03, Akhil P Oommen wrote: >> On 6/22/2018 6:41 AM, Ezequiel Garcia wrote: >>> Hey Enric, >>> >>> On Fri, 2018-06-22 at 00:04 +0200, Enric Balletbo i Serra wrote: >>>> When the devfreq driver and the governor driver are built as modules, >>>> the call to devfreq_add_device() or governor_store() fails because >>>> the >>>> governor driver is not loaded at the time the devfreq driver loads. >>>> The >>>> devfreq driver has a build dependency on the governor but also should >>>> have a runtime dependency. We need to make sure that the governor >>>> driver >>>> is loaded before the devfreq driver. >>>> >>>> This patch fixes this bug by adding a try_then_request_governor() >>>> function. First tries to find the governor, and then, if it is not >>>> found, >>>> it requests the module and tries again. >>>> >>>> Fixes: 1b5c1be2c88e (PM / devfreq: map devfreq drivers to governor >>>> using name) >>>> Signed-off-by: Enric Balletbo i Serra >>>> --- >>>> >>>> Changes in v3: >>>> - Remove unneded change in dev_err message. >>>> - Fix err returned value in case to not find the governor. >>>> >>>> Changes in v2: >>>> - Add a new function to request the module and call that function >>>> from >>>>    devfreq_add_device and governor_store. >>>> >>>>   drivers/devfreq/devfreq.c | 65 ++++++++++++++++++++++++++++++++----- >>>> -- >>> [snip snip] >>>> -    governor = find_devfreq_governor(devfreq->governor_name); >>>> +    governor = try_then_request_governor(devfreq- >>>>> governor_name); >>>>       if (IS_ERR(governor)) { >>>>           dev_err(dev, "%s: Unable to find governor for the >>>> device\n", >>>>               __func__); >>>>           err = PTR_ERR(governor); >>>> -        goto err_init; >>>> +        goto err_unregister; >>>>       } >>>>   +    mutex_lock(&devfreq_list_lock); >>>> + >>> I know it's not something we are introducing in this patch, >>> but still... calling a hook with a mutex held looks >>> fishy to me. >>> >>> This lock should only protect the list, unless I am missing >>> something. >>> > I think so too. > >>>>       devfreq->governor = governor; >>>>       err = devfreq->governor->event_handler(devfreq, >>>> DEVFREQ_GOV_START, >>>>                           NULL); >>>> @@ -663,14 +703,16 @@ struct devfreq *devfreq_add_device(struct >>>> device *dev, >>>>               __func__); >>>>           goto err_init; >>>>       } >>>> + >>>> +    list_add(&devfreq->node, &devfreq_list); >>>> + >>>>       mutex_unlock(&devfreq_list_lock); >>>>         return devfreq; >>>>     err_init: >>>> -    list_del(&devfreq->node); >>>>       mutex_unlock(&devfreq_list_lock); >>>> - >>>> +err_unregister: >>>>       device_unregister(&devfreq->dev); >>>>   err_dev: >>>>       if (devfreq) >>>> @@ -988,12 +1030,13 @@ static ssize_t governor_store(struct device >>>> *dev, struct device_attribute *attr, >>>>       if (ret != 1) >>>>           return -EINVAL; >>>>   -    mutex_lock(&devfreq_list_lock); >>>> -    governor = find_devfreq_governor(str_governor); >>>> +    governor = try_then_request_governor(str_governor); >>>>       if (IS_ERR(governor)) { >>>> -        ret = PTR_ERR(governor); >>>> -        goto out; >>>> +        return PTR_ERR(governor); >>>>       } >>>> + >>>> +    mutex_lock(&devfreq_list_lock); >>>> + >>>>       if (df->governor == governor) { >>>>           ret = 0; >>>>           goto out; >>>> -- >>>> 2.17.1 >>>> >>>> >>> Regards, >>> Eze >> Adding to Ezequiel's point, shouldn't we take more granular lock (devfreq->lock) >> first and then call devfreq_list_lock at the time of adding to the list? >> > Yes, I think so. I think, though, that this should be a separate patch, not sure > if a pre or post patch to this one, but for sure it's another topic. Current > patch tries to solve different problem an only tries to follow the current > locking/unlocking. Anyway this is a maintainer decision I guess. > > Thanks, > Enric > >> -Akhil. >> I agree. -Akhil.