linux-kernel - Re: [PATCH v2] ptp: free ptp clock properly

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Date:   Fri, 3 Apr 2020 09:34:14 -0400 (EDT)
From:   Vladis Dronov <vdronov@...hat.com>
To:     Andrea Righi <andrea.righi@...onical.com>,
        Colin Ian King <colin.king@...onical.com>
Cc:     Richard Cochran <richardcochran@...il.com>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] ptp: free ptp clock properly

Hello, Andrea, Colin, all,

This fix is really not needed, as its creation is based on the assumption
that the Ubuntu kernel 5.3.0-40-generic has the upstream commit 75718584cb3c,
which is the real fix to this crash.

> > > I would guess that a kernel in question (5.3.0-40-generic) has the commit
> > > a33121e5487b but does not have the commit 75718584cb3c, which should be
> > > exactly fixing a docking station disconnect crash. Could you please,
> > > check this?
> >
> > Unfortunately the kernel in question already has 75718584cb3c:
> > https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/bionic/commit/?h=hwe&id=c71b774732f997ef38ed7bd62e73891a01f2bbfe

Apologies, but the assumption above is not correct, 5.3.0-40-generic does
not have 75718584cb3c. If it had 75718584cb3c it would be a fix and the ptp-related
crash (described in https://bugs.launchpad.net/bugs/1864754) would not happen.

This way https://lists.ubuntu.com/archives/kernel-team/2020-March/108562.html fix
is not really needed.

Best regards,
Vladis Dronov | Red Hat, Inc. | The Core Kernel | Senior Software Engineer

----- Original Message -----
> From: "Andrea Righi" <andrea.righi@...onical.com>
> To: "Richard Cochran" <richardcochran@...il.com>, "Vladis Dronov" <vdronov@...hat.com>
> Cc: "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org, linux-kernel@...r.kernel.org
> Sent: Monday, March 9, 2020 6:22:38 PM
> Subject: [PATCH v2] ptp: free ptp clock properly
> 
> There is a bug in ptp_clock_unregister() where pps_unregister_source()
> can free up resources needed by posix_clock_unregister() to properly
> destroy a related sysfs device.
> 
> Fix this by calling pps_unregister_source() in ptp_clock_release().
> 
> See also:
> commit 75718584cb3c ("ptp: free ptp device pin descriptors properly").
> 
> BugLink: https://bugs.launchpad.net/bugs/1864754
> Fixes: a33121e5487b ("ptp: fix the race between the release of ptp_clock and
> cdev")
> Tested-by: Piotr Morgwai Kotarbiński <foss@...gwai.pl>
> Signed-off-by: Andrea Righi <andrea.righi@...onical.com>
> ---
> 
> v2: move pps_unregister_source() to ptp_clock_release(), instead of
>     posix_clock_unregister(), that would just introduce a resource leak
> 
>  drivers/ptp/ptp_clock.c | 8 +++-----
>  1 file changed, 3 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/ptp/ptp_clock.c b/drivers/ptp/ptp_clock.c
> index ac1f2bf9e888..468286ef61ad 100644
> --- a/drivers/ptp/ptp_clock.c
> +++ b/drivers/ptp/ptp_clock.c
> @@ -170,6 +170,9 @@ static void ptp_clock_release(struct device *dev)
>  {
>  	struct ptp_clock *ptp = container_of(dev, struct ptp_clock, dev);
>  
> +	/* Release the clock's resources. */
> +	if (ptp->pps_source)
> +		pps_unregister_source(ptp->pps_source);
>  	ptp_cleanup_pin_groups(ptp);
>  	mutex_destroy(&ptp->tsevq_mux);
>  	mutex_destroy(&ptp->pincfg_mux);
> @@ -298,11 +301,6 @@ int ptp_clock_unregister(struct ptp_clock *ptp)
>  		kthread_cancel_delayed_work_sync(&ptp->aux_work);
>  		kthread_destroy_worker(ptp->kworker);
>  	}
> -
> -	/* Release the clock's resources. */
> -	if (ptp->pps_source)
> -		pps_unregister_source(ptp->pps_source);
> -
>  	posix_clock_unregister(&ptp->clock);
>  
>  	return 0;
> --
> 2.25.0