linux-kernel - Re: [PATCH v2 2/2] tty: use tty_init_dev_retry() to workaround a race condition

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Date:   Sun, 24 Nov 2019 00:02:33 +0000
From:   Sudip Mukherjee <sudipm.mukherjee@...il.com>
To:     Jiri Slaby <jslaby@...e.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] tty: use tty_init_dev_retry() to workaround a
 race condition

On Fri, Nov 22, 2019 at 10:11:26AM +0100, Jiri Slaby wrote:
> On 22. 11. 19, 10:05, Jiri Slaby wrote:
> > On 21. 11. 19, 22:01, Sudip Mukherjee wrote:
> >> Hi Greg,
> >>
> >> On Thu, Nov 21, 2019 at 05:41:38PM +0100, Greg Kroah-Hartman wrote:
> >>> On Thu, Nov 21, 2019 at 03:22:39PM +0000, Sudip Mukherjee wrote:
> >>>> There seems to be a race condition in tty drivers and I could see on
> >>>> many boot cycles a NULL pointer dereference as tty_init_dev() tries to

<snip>

> > 
> > Interferences of console vs tty code are ugly. Does it help to simply
> > put tty_port_link_device to uart_add_one_port before uart_configure_port?
> 
> Alternatively, you can try setting tty_port in uart_install by:
> tty->port = &state->port.

I have not tried these. will try.

> 
> BTW do you see the warning from tty_init_dev:
> "driver does not set tty->port. This will crash the kernel later. Fix
> the driver!\n"
> ? Maybe not given console is registered already, but crashes.

yes. I do see the warning but I have always assumed that the warning is
because console is openend as soon as it registers and so uart_add_one_port()
does not get the chance to link it. Is it not so?

--
Regards
Sudip