linux-kernel - Re: [PATCH v4 1/1] power: Emit changed uevent on wakeup_sysfs

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Date:   Tue, 7 Jul 2020 19:16:31 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Abhishek Pandit-Subedi <abhishekpandit@...omium.org>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        "open list:BLUETOOTH DRIVERS" <linux-bluetooth@...r.kernel.org>,
        ChromeOS Bluetooth Upstreaming 
        <chromeos-bluetooth-upstreaming@...omium.org>,
        Rafael Wysocki <rafael.j.wysocki@...el.com>,
        Stephen Boyd <swboyd@...omium.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>
Subject: Re: [PATCH v4 1/1] power: Emit changed uevent on wakeup_sysfs_add/remove

On Tue, Jul 7, 2020 at 6:48 PM Abhishek Pandit-Subedi
<abhishekpandit@...omium.org> wrote:
>
> Hi Rafael,
>
> (resent in plain text)
>
> On Tue, Jul 7, 2020 at 9:28 AM Rafael J. Wysocki <rafael@...nel.org> wrote:
> >
> > On Tue, Jul 7, 2020 at 6:24 PM Abhishek Pandit-Subedi
> > <abhishekpandit@...omium.org> wrote:
> > >
> > > Udev rules that depend on the power/wakeup attribute don't get triggered
> > > correctly if device_set_wakeup_capable is called after the device is
> > > created. This can happen for several reasons (driver sets wakeup after
> > > device is created, wakeup is changed on parent device, etc) and it seems
> > > reasonable to emit a changed event when adding or removing attributes on
> > > the device.
> > >
> > > Signed-off-by: Abhishek Pandit-Subedi <abhishekpandit@...omium.org>
> > > ---
> > >
> > > Changes in v4:
> > > - Fix warning where returning from void and tested on device
> > >
> > > Changes in v3:
> > > - Simplified error handling
> > >
> > > Changes in v2:
> > > - Add newline at end of bt_dev_err
> > >
> > >  drivers/base/power/sysfs.c | 9 ++++++++-
> > >  1 file changed, 8 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/base/power/sysfs.c b/drivers/base/power/sysfs.c
> > > index 24d25cf8ab1487..aeb58d40aac8de 100644
> > > --- a/drivers/base/power/sysfs.c
> > > +++ b/drivers/base/power/sysfs.c
> > > @@ -1,6 +1,7 @@
> > >  // SPDX-License-Identifier: GPL-2.0
> > >  /* sysfs entries for device PM */
> > >  #include <linux/device.h>
> > > +#include <linux/kobject.h>
> > >  #include <linux/string.h>
> > >  #include <linux/export.h>
> > >  #include <linux/pm_qos.h>
> > > @@ -739,12 +740,18 @@ int dpm_sysfs_change_owner(struct device *dev, kuid_t kuid, kgid_t kgid)
> > >
> > >  int wakeup_sysfs_add(struct device *dev)
> > >  {
> > > -       return sysfs_merge_group(&dev->kobj, &pm_wakeup_attr_group);
> > > +       int ret = sysfs_merge_group(&dev->kobj, &pm_wakeup_attr_group);
> > > +
> > > +       if (ret)
> > > +               return ret;
> > > +
> > > +       return kobject_uevent(&dev->kobj, KOBJ_CHANGE);
> >
> > So let me repeat the previous comment:
> >
> > If you return an error here, it may confuse the caller to think that
> > the operation has failed completely, whereas the merging of the
> > attribute group has been successful already.
> >
> > I don't think that an error can be returned at this point.
> >
>
> The caller looks at the return code and just logs that an error
> occurred (no other action). It's also unlikely for kobject_uevent to
> fail (I saw mostly -ENOMEM and an -ENOENT when the kobj wasn't in the
> correct set).
>
> Call site:
>     int ret = wakeup_sysfs_add(dev);
>
>     if (ret)
>         dev_info(dev, "Wakeup sysfs attributes not added\n");

Yes, which is confusing, because the wakeup attributes may in fact
have been added.  Which is my point.

>
> So I'm ok with either keeping this as-is (caller isn't getting
> confused, just logging) or swallowing the return of kobject_uevent.

I would just ignore the return value of kobject_uevent() along the
lines of wakeup_sysfs_remove() below.

Thanks!

> > >  }
> > >
> > >  void wakeup_sysfs_remove(struct device *dev)
> > >  {
> > >         sysfs_unmerge_group(&dev->kobj, &pm_wakeup_attr_group);
> > > +       kobject_uevent(&dev->kobj, KOBJ_CHANGE);
> > >  }
> > >
> > >  int pm_qos_sysfs_add_resume_latency(struct device *dev)
> > > --
> > > 2.27.0.212.ge8ba1cc988-goog
> > >