From: Jiri Slaby <jslaby@suse.com>
To: Sudip Mukherjee <sudipm.mukherjee@gmail.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 2/2] tty: use tty_init_dev_retry() to workaround a race condition
Date: Fri, 22 Nov 2019 10:05:09 +0100 [thread overview]
Message-ID: <eef58b47-f208-2ac5-6e02-a87f9568c70f@suse.com> (raw)
In-Reply-To: <20191121210155.limd7v6cpd5yz2e7@debian>
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
>>> do 'tty->port->itty = tty' even though tty->port is NULL.
>>> 'tty->port' will be set by the driver and if the driver has not yet done
>>> it before we open the tty device we can get to this situation. By adding
>>> some extra debug prints, I noticed that:
>>>
>>> 6.650130: uart_add_one_port
>>> 6.663849: register_console
>>> 6.664846: tty_open
>>> 6.674391: tty_init_dev
>>> 6.675456: tty_port_link_device
>>>
>>> uart_add_one_port() registers the console, as soon as it registers, the
>>> userspace tries to use it and that leads to tty_open() but
>>> uart_add_one_port() has not yet done tty_port_link_device() and so
>>> tty->port is not yet configured when control reaches tty_init_dev().
>>
>> Shouldn't we do tty_port_link_device() before uart_add_one_port() to
>> remove that race? Once you register the console, yes, tty_open() can
>> happen, so the driver had better be ready to go at that point in time.
>>
>
> But tty_port_link_device() is done by uart_add_one_port() itself.
> After registering the console uart_add_one_port() will call
> tty_port_register_device_attr_serdev() and tty_port_link_device() is
> called from this. Thats still tty core.
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?
thanks,
--
js
suse labs
next prev parent reply other threads:[~2019-11-22 9:05 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-21 15:22 [PATCH v2 1/2] tty: add retry capability to tty_init_dev() Sudip Mukherjee
2019-11-21 15:22 ` [PATCH v2 2/2] tty: use tty_init_dev_retry() to workaround a race condition Sudip Mukherjee
2019-11-21 16:41 ` Greg Kroah-Hartman
2019-11-21 21:01 ` Sudip Mukherjee
2019-11-22 9:05 ` Jiri Slaby [this message]
2019-11-22 9:11 ` Jiri Slaby
2019-11-24 0:02 ` Sudip Mukherjee
2019-11-25 10:42 ` Jiri Slaby
2019-12-10 11:41 ` Sudip Mukherjee
2019-12-12 11:15 ` Greg Kroah-Hartman
2019-12-17 11:47 ` Sudip Mukherjee
2019-12-17 12:05 ` Greg Kroah-Hartman
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=eef58b47-f208-2ac5-6e02-a87f9568c70f@suse.com \
--to=jslaby@suse.com \
--cc=gregkh@linuxfoundation.org \
--cc=linux-kernel@vger.kernel.org \
--cc=sudipm.mukherjee@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).