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Message-ID: <2023110139-dupe-snipping-5700@gregkh>
Date: Wed, 1 Nov 2023 18:54:07 +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 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?
Also, I think you just leaked a reference count here, how was this
tested?
thanks,
greg k-h
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