From: Ezequiel Garcia <ezequiel@collabora.com>
To: Enric Balletbo Serra <eballetbo@gmail.com>
Cc: Kyungmin Park <kyungmin.park@samsung.com>,
MyungJoo Ham <myungjoo.ham@samsung.com>,
kernel@collabora.com, Linux PM list <linux-pm@vger.kernel.org>,
Enric Balletbo i Serra <enric.balletbo@collabora.com>
Subject: Re: [PATCH 1/2] PM / devfreq: Fix governor module load failure
Date: Thu, 06 Jun 2019 10:42:46 -0300 [thread overview]
Message-ID: <8d2362309dee4ac066086033996a40da45d92fed.camel@collabora.com> (raw)
In-Reply-To: <CAFqH_52c42_SD9VLwnGXtP2V0ZCpmynTMqgHgA2JUmK_jdMcVw@mail.gmail.com>
On Wed, 2019-06-05 at 23:46 +0200, Enric Balletbo Serra wrote:
> Hi Ezequiel,
>
> Missatge de Ezequiel Garcia <ezequiel@collabora.com> del dia dc., 5 de
> juny 2019 a les 21:06:
> > A bit unexpectedly (but still documented), request_module may
> > return a positive value, in case of a modprobe error.
> > This is currently causing issues in the devfreq framework.
> >
> > When a request_module exits with a positive value, we currently
> > return that via ERR_PTR. However, because the value is positive,
> > it's not a ERR_VALUE proper, and is therefore treated as a
> > valid struct devfreq_governor pointer, leading to a kernel oops.
> >
> > The right way to fix this is hinted in __request_module documentation:
> >
> > """
> > [snip] The function returns
> > zero on success or a negative errno code or positive exit code from
> > "modprobe" on failure. Note that a successful module load does not mean
> > the module did not then unload and exit on an error of its own. Callers
> > must check that the service they requested is now available not blindly
> > invoke it.
> > """
> >
> > Therefore, drop the return value check, which is not useful, and instead
> > just re-try to find the (hopefully now loaded) governor.
> >
> > Fixes: 23c7b54ca1cd1 ("PM / devfreq: Fix devfreq_add_device() when drivers are built as modules.")
>
> I think that what you really fixed is a bug introduced by:
>
> b53b0128052ff ("PM / devfreq: Fix static checker warning in
> try_then_request_governor")
>
> not the above commit.
>
Oh, you are right of course. I looked for the commit introducing the
request_module usage, and thought it was the culprit.
> > Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
> > ---
> > drivers/devfreq/devfreq.c | 8 ++------
> > 1 file changed, 2 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
> > index 6b6991f0e873..8868ad9472d2 100644
> > --- a/drivers/devfreq/devfreq.c
> > +++ b/drivers/devfreq/devfreq.c
> > @@ -236,7 +236,6 @@ static struct devfreq_governor *find_devfreq_governor(const char *name)
> > static struct devfreq_governor *try_then_request_governor(const char *name)
> > {
> > struct devfreq_governor *governor;
> > - int err = 0;
> >
> > if (IS_ERR_OR_NULL(name)) {
> > pr_err("DEVFREQ: %s: Invalid parameters\n", __func__);
> > @@ -251,13 +250,10 @@ static struct devfreq_governor *try_then_request_governor(const char *name)
> >
> > if (!strncmp(name, DEVFREQ_GOV_SIMPLE_ONDEMAND,
> > DEVFREQ_NAME_LEN))
> > - err = request_module("governor_%s", "simpleondemand");
> > + request_module("governor_%s", "simpleondemand");
> > else
> > - err = request_module("governor_%s", name);
> > - /* Restore previous state before return */
> > + request_module("governor_%s", name);
> > mutex_lock(&devfreq_list_lock);
> > - if (err)
>
> If you remove this check you'll iterate always over the full devfreq
> list of governors, I know should be quick and is not too long but ...
>
Keep in mind that when the request_module succeeds, we need
to iterate anyways to find the governor.
> > - return ERR_PTR(err);
>
> The fix can be simply:
>
> return ERR_PTR(-EINVAL);
>
> I don't think overlap the real error is a problem here.
>
Yeah, I also thought about this, but somehow thought this
was simpler.
I don't have a strong opinion, so whatever you prefer is fine.
Thanks,
Eze
> Thanks,
> Enric
>
> > governor = find_devfreq_governor(name);
> > }
> > --
> > 2.20.1
> >
next prev parent reply other threads:[~2019-06-06 13:42 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CGME20190605190147epcas1p3e74fba524dfcfc87f7ce3c9569ffaa3f@epcas1p3.samsung.com>
2019-06-05 19:00 ` [PATCH 1/2] PM / devfreq: Fix governor module load failure Ezequiel Garcia
2019-06-05 19:00 ` [PATCH 2/2] PM / devfreq: Sanitize prints Ezequiel Garcia
2019-06-20 7:23 ` Chanwoo Choi
2019-06-20 14:41 ` Ezequiel Garcia
2019-06-21 2:53 ` Chanwoo Choi
2019-06-05 21:46 ` [PATCH 1/2] PM / devfreq: Fix governor module load failure Enric Balletbo Serra
2019-06-06 13:42 ` Ezequiel Garcia [this message]
2019-06-06 13:48 ` Enric Balletbo i Serra
2019-06-20 7:59 ` Chanwoo Choi
2019-06-20 8:04 ` Chanwoo Choi
2019-06-20 15:31 ` Ezequiel Garcia
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