linux-kernel - Re: [PATCH] thermal/thresholds: Fix thermal lock annotation issue

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Message-ID: <CAJZ5v0gF=B7NG0ZVCHr4DfSqYaunDLw1Bcpjqcf1NwLBW_jNEw@mail.gmail.com>
Date: Thu, 24 Oct 2024 15:17:16 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Daniel Lezcano <daniel.lezcano@...aro.org>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, 
	syzbot+f24dd060c1911fe54c85@...kaller.appspotmail.com, 
	Zhang Rui <rui.zhang@...el.com>, Lukasz Luba <lukasz.luba@....com>, 
	"open list:THERMAL" <linux-pm@...r.kernel.org>, open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] thermal/thresholds: Fix thermal lock annotation issue

On Thu, Oct 24, 2024 at 12:36 PM Daniel Lezcano
<daniel.lezcano@...aro.org> wrote:
>
>
> Hi,
>
> please note this fix has been written on top of the thermal thresholds
> series, so I don't know how it conflicts if it is applied before

No worries.

Applied (on top of the thresholds series).

> On 24/10/2024 12:23, Daniel Lezcano wrote:
> > When the thermal zone is unregistered (thermal sensor module being
> > unloaded), no lock is held when flushing the thresholds. That results
> > in a WARN when the lockdep validation is set in the kernel config.
> >
> > This has been reported by syzbot.
> >
> > As the thermal zone is in the process of being destroyed, there is no
> > need to send a notification about purging the thresholds to the
> > userspace as this one will receive a thermal zone deletion
> > notification which imply the deletion of all the associated resources
> > like the trip points or the user thresholds.
> >
> > Split the function thermal_thresholds_flush() into a lockless one
> > without notification and its call with the lock annotation followed
> > with the thresholds flushing notification.
> >
> > Please note this scenario is unlikely to happen, as the sensor drivers
> > are usually compiled-in in order to have the thermal framework to be
> > able to kick in at boot time if needed.
> >
> > Link: https://lore.kernel.org/all/67124175.050a0220.10f4f4.0012.GAE@google.com
> > Reported-by: syzbot+f24dd060c1911fe54c85@...kaller.appspotmail.com
> > Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>
> > ---
> >   drivers/thermal/thermal_thresholds.c | 13 +++++++++----
> >   1 file changed, 9 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/thermal/thermal_thresholds.c b/drivers/thermal/thermal_thresholds.c
> > index ea4aa5a2e86c..2888eabd3efe 100644
> > --- a/drivers/thermal/thermal_thresholds.c
> > +++ b/drivers/thermal/thermal_thresholds.c
> > @@ -20,17 +20,22 @@ int thermal_thresholds_init(struct thermal_zone_device *tz)
> >       return 0;
> >   }
> >
> > -void thermal_thresholds_flush(struct thermal_zone_device *tz)
> > +static void __thermal_thresholds_flush(struct thermal_zone_device *tz)
> >   {
> >       struct list_head *thresholds = &tz->user_thresholds;
> >       struct user_threshold *entry, *tmp;
> >
> > -     lockdep_assert_held(&tz->lock);
> > -
> >       list_for_each_entry_safe(entry, tmp, thresholds, list_node) {
> >               list_del(&entry->list_node);
> >               kfree(entry);
> >       }
> > +}
> > +
> > +void thermal_thresholds_flush(struct thermal_zone_device *tz)
> > +{
> > +     lockdep_assert_held(&tz->lock);
> > +
> > +     __thermal_thresholds_flush(tz);
> >
> >       thermal_notify_threshold_flush(tz);
> >
> > @@ -39,7 +44,7 @@ void thermal_thresholds_flush(struct thermal_zone_device *tz)
> >
> >   void thermal_thresholds_exit(struct thermal_zone_device *tz)
> >   {
> > -     thermal_thresholds_flush(tz);
> > +     __thermal_thresholds_flush(tz);
> >   }
> >
> >   static int __thermal_thresholds_cmp(void *data,
>
>
> --
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