linux-kernel - Re: [PATCH] usb: musb: sunxi: Explicitly release USB PHY on exit

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Date:   Tue, 10 Oct 2017 13:43:51 +1100
From:   Jonathan Liu <net147@...il.com>
To:     Bin Liu <b-liu@...com>, Jonathan Liu <net147@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Maxime Ripard <maxime.ripard@...e-electrons.com>,
        Chen-Yu Tsai <wens@...e.org>, linux-usb@...r.kernel.org,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-sunxi <linux-sunxi@...glegroups.com>
Subject: Re: [PATCH] usb: musb: sunxi: Explicitly release USB PHY on exit

Hi,

On 10 October 2017 at 13:14, Bin Liu <b-liu@...com> wrote:
> On Tue, Oct 10, 2017 at 08:17:34AM +1100, Jonathan Liu wrote:
>> Hi,
>>
>> On 10 October 2017 at 01:23, Bin Liu <b-liu@...com> wrote:
>> > Hi,
>> >
>> > On Tue, Sep 26, 2017 at 09:39:23PM +1000, Jonathan Liu wrote:
>> >> This fixes a kernel oops when unloading the driver due to usb_put_phy
>> >> being called after usb_phy_generic_unregister when the device is
>> >> detached. Calling usb_phy_generic_unregister causes x->dev->driver to
>> >> be NULL in usb_put_phy and results in a NULL pointer dereference.
>> >>
>> >> As we are now explicitly managing the lifetime of usb_phy,
>> >> devm_usb_get_phy is changed to usb_get_phy and we call usb_put_phy in
>> >> the probe error path.
>> >>
>> >> Cc: stable@...r.kernel.org # v4.3+
>> >> Signed-off-by: Jonathan Liu <net147@...il.com>
>> >> ---
>> >>  drivers/usb/musb/sunxi.c | 8 ++++++--
>> >>  1 file changed, 6 insertions(+), 2 deletions(-)
>> >>
>> >> diff --git a/drivers/usb/musb/sunxi.c b/drivers/usb/musb/sunxi.c
>> >> index c9a09b5bb6e5..8eed61042103 100644
>> >> --- a/drivers/usb/musb/sunxi.c
>> >> +++ b/drivers/usb/musb/sunxi.c
>> >> @@ -297,6 +297,8 @@ static int sunxi_musb_exit(struct musb *musb)
>> >>       if (test_bit(SUNXI_MUSB_FL_HAS_SRAM, &glue->flags))
>> >>               sunxi_sram_release(musb->controller->parent);
>> >>
>> >> +     usb_put_phy(glue->xceiv);
>> >
>> > Will devm_usb_put_phy() solve the issue too? Then you don't need the
>> > changes in sunxi_musb_probe() below.
>> >
>>
>> devm_usb_put_phy does solve the issue without changes in
>> sunxi_musb_probe but I think it is clearer that the lifetime is
>> explicitly managed if we don't mix implicit and explicit freeing of
>> resources.
>
> Then what is the purpose of the devm_* API?
>
> The original bug was that devm_usb_get_phy() is called in _probe, but
> devm_usb_put_phy() was never called, which caused the device ref count
> unbalanced. It is not related to implicit/explicit resource management.
>
> devm_* is recommended whenever applicable.
>

Ok. Will use devm_usb_put_phy in v2 patch.

> Regards,
> -Bin.
>

Regards,
Jonathan