linux-kernel - Re: [PATCH] drivers core: lookup sysfs power group before removal

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Date:   Fri, 3 Nov 2023 19:36:21 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     José Pekkarinen <jose.pekkarinen@...hound.fi>
Cc:     rafael@...nel.org, len.brown@...el.com, pavel@....cz,
        skhan@...uxfoundation.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        syzbot+95f2e2439b97575ec3c0@...kaller.appspotmail.com
Subject: Re: [PATCH] drivers core: lookup sysfs power group before removal

On Fri, Nov 03, 2023 at 07:49:39PM +0200, José Pekkarinen wrote:
> On 2023-11-01 19:54, Greg KH wrote:
> > On Wed, Nov 01, 2023 at 07:36:27PM +0200, José Pekkarinen wrote:
> > > Hinted by syzboot, there is a few cases where the sysfs power group
> > > may
> > > not be there, like the failure while adding it, or adding its runtime
> > > group, or when the sysfs firmware loader fallback fail to populate. In
> > > the last case, the device_del function will be called leading to
> > > attempt
> > > to remove the sysfs group. This patch will lookup for it in advance to
> > > grant that it is effectively there before cleaning it up.
> > > 
> > > Reported-by: syzbot+95f2e2439b97575ec3c0@...kaller.appspotmail.com
> > > 
> > > Signed-off-by: José Pekkarinen <jose.pekkarinen@...hound.fi>
> > > ---
> > >  drivers/base/power/sysfs.c | 4 +++-
> > >  1 file changed, 3 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/base/power/sysfs.c b/drivers/base/power/sysfs.c
> > > index a1474fb67db9..6601729c4698 100644
> > > --- a/drivers/base/power/sysfs.c
> > > +++ b/drivers/base/power/sysfs.c
> > > @@ -834,5 +834,7 @@ void dpm_sysfs_remove(struct device *dev)
> > >  	dev_pm_qos_constraints_destroy(dev);
> > >  	rpm_sysfs_remove(dev);
> > >  	sysfs_unmerge_group(&dev->kobj, &pm_wakeup_attr_group);
> > > -	sysfs_remove_group(&dev->kobj, &pm_attr_group);
> > > +
> > > +	if (kernfs_find_and_get((&dev->kobj)->sd, pm_attr_group.name))
> > > +		sysfs_remove_group(&dev->kobj, &pm_attr_group);
> > 
> > What's to keep it from going away right after finding it?
> > 
> > In other words, what is wrong with removing a group that is not there?
> > What error happens?  It should be fine, or are you seeing real code
> > failures somewhere?
> 
>     No, this is just hitting a warning that sysbot complains about by
> setting panic on warning, no big deal, though it can be a wrong behaviour
> in ueagle-atm driver, since it defines to disconnect the device if the
> firmware is not there, no matter the sysfs fallback.

Then fix the driver please.

And what warning are you seeing exactly?

thanks,

greg k-h