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Date:   Sat, 9 Nov 2019 15:49:13 +0800
From:   hui yang <yanghui.def@...il.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     balbi@...nel.org, mirq-linux@...e.qmqm.pl,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] USB(u_serial.c): it has a NULL point

I'm sorry for my fault . Now I send to everyone .

When we use USB to transmit data
with PC, the phone will crashed Low probability .
We found port->port.tty became NULL.

Thanks

Greg KH <gregkh@...uxfoundation.org> 于2019年11月3日周日 下午8:42写道:
>
> On Sun, Nov 03, 2019 at 10:44:04AM +0800, hui yang wrote:
> > From: YangHui <yanghui.def@...il.com>
> >
> > Unable to handle kernel NULL pointer dereference at virtual address 000002a0
> > Kernel BUG at tty_wakeup+0x18/0x8c
> > [<0000000095135e9d>] tty_wakeup+0x18/0x8c
> > [<00000000c35f19e4>] gs_start_io+0xc8/0x158
> > [<00000000b11b184e>] gserial_connect+0xd0/0x174
> > [<00000000642201de>] acm_set_alt+0x70/0x180
> > [<00000000a9d38e8b>] composite_setup+0x1848/0x1a7c
> > [<0000000072c88781>] android_setup+0x1ec/0x1f4
> > [<000000004c0127a5>] msm_udc_irq+0x8d0/0xc0c
> > [<00000000f8bb9acf>] __handle_irq_event_percpu+0x74/0x294
> > [<00000000afd57256>] handle_irq_event+0x60/0xc8
> > [<0000000076719b24>] handle_fasteoi_irq+0xc8/0x1c4
> > [<00000000421f3d87>] generic_handle_irq+0x34/0x4c
> > [<00000000b2f2d343>] __handle_domain_irq+0x6c/0xbc
> > [<00000000c74325e8>] gic_handle_irq+0x6c/0xe0
> > yes,we can see the port->port.tty==NULL, so system crashed
> >
> > Signed-off-by: YangHui <yanghui.def@...il.com>
> > ---
> >  drivers/usb/gadget/function/u_serial.c | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/drivers/usb/gadget/function/u_serial.c b/drivers/usb/gadget/function/u_serial.c
> > index 65f634e..a1c2ac2 100644
> > --- a/drivers/usb/gadget/function/u_serial.c
> > +++ b/drivers/usb/gadget/function/u_serial.c
> > @@ -562,6 +562,8 @@ static int gs_start_io(struct gs_port *port)
> >
> >       /* unblock any pending writes into our circular buffer */
> >       if (started) {
> > +             if (port->port.tty == NULL)
> > +                     return -EIO;
>
> How can this happen?  Shouldn't this be handled earlier?
>
> If not, can you document this how this can be true and what should be
> done about it?
>
> thanks,
>
> greg k-h

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