netdev - Re: [PATCH] ptp: free ptp clock properly

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Date:   Wed, 4 Mar 2020 15:11:44 -0500 (EST)
From:   Vladis Dronov <vdronov@...hat.com>
To:     Andrea Righi <andrea.righi@...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] ptp: free ptp clock properly

Hello, Andrea, all,

----- Original Message -----
> From: "Andrea Righi" <andrea.righi@...onical.com>
> Subject: [PATCH] ptp: free ptp clock properly
> 
> There is a bug in ptp_clock_unregister() where ptp_clock_release() can
> free up resources needed by posix_clock_unregister() to properly destroy
> a related sysfs device.
> 
> Fix this by calling posix_clock_unregister() in ptp_clock_release().

Honestly, this does not seem right. The calls at PTP clock release are:

ptp_clock_unregister() -> posix_clock_unregister() -> cdev_device_del() ->
-> ... bla ... -> ptp_clock_release()

So, it looks like with this patch both posix_clock_unregister() and
ptp_clock_release() are not called at all. And it looks like the "fix" is
not removing PTP clock's cdev, i.e. leaking it and related sysfs resources.

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?

Why? We have 2 crash call traces. 1) the launchpad bug 2) the email which
led to the commit 75718584cb3c creation (see Link:).

Aaaaand they are identical starting from device_release_driver_internal()
and almost to the top.

> 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")
> Signed-off-by: Andrea Righi <andrea.righi@...onical.com>
> ---
>  drivers/ptp/ptp_clock.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/ptp/ptp_clock.c b/drivers/ptp/ptp_clock.c
> index ac1f2bf9e888..12951023d0c6 100644
> --- a/drivers/ptp/ptp_clock.c
> +++ b/drivers/ptp/ptp_clock.c
> @@ -171,6 +171,7 @@ static void ptp_clock_release(struct device *dev)
>  	struct ptp_clock *ptp = container_of(dev, struct ptp_clock, dev);
>  
>  	ptp_cleanup_pin_groups(ptp);
> +	posix_clock_unregister(&ptp->clock);
>  	mutex_destroy(&ptp->tsevq_mux);
>  	mutex_destroy(&ptp->pincfg_mux);
>  	ida_simple_remove(&ptp_clocks_map, ptp->index);
> @@ -303,8 +304,6 @@ int ptp_clock_unregister(struct ptp_clock *ptp)
>  	if (ptp->pps_source)
>  		pps_unregister_source(ptp->pps_source);
>  
> -	posix_clock_unregister(&ptp->clock);
> -
>  	return 0;
>  }
>  EXPORT_SYMBOL(ptp_clock_unregister);
> --
> 2.25.0

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