From: Andy Shevchenko <andy.shevchenko@gmail.com>
To: Tycho Andersen <tycho@tycho.ws>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Jiri Slaby <jslaby@suse.com>,
"open list:SERIAL DRIVERS" <linux-serial@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
"Serge E . Hallyn" <serge@hallyn.com>
Subject: Re: [PATCH v3] uart: fix race between uart_put_char() and uart_shutdown()
Date: Fri, 6 Jul 2018 19:49:09 +0300 [thread overview]
Message-ID: <CAHp75Vfbh5SzpqP=2LfeXteEGrBG46dPfeHsU0ac5SiJSjZOXw@mail.gmail.com> (raw)
In-Reply-To: <20180706162457.20489-1-tycho@tycho.ws>
On Fri, Jul 6, 2018 at 7:24 PM, Tycho Andersen <tycho@tycho.ws> wrote:
> Looking in uart_port_startup(), it seems that circ->buf (state->xmit.buf)
> protected by the "per-port mutex", which based on uart_port_check() is
> state->port.mutex. Indeed, the lock acquired in uart_put_char() is
> uport->lock, i.e. not the same lock.
>
> Anyway, since the lock is not acquired, if uart_shutdown() is called, the
> last chunk of that function may release state->xmit.buf before its assigned
> to null, and cause the race above.
>
> To fix it, let's lock uport->lock when allocating/deallocating
> state->xmit.buf in addition to the per-port mutex.
Thanks for fixing this!
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Some nitpicks though.
> + unsigned long page, flags = 0;
I would rather put on separate lines and btw assignment is not needed.
It all goes through macros.
> - if (!state->xmit.buf) {
> - /* This is protected by the per port mutex */
> - page = get_zeroed_page(GFP_KERNEL);
> - if (!page)
> - return -ENOMEM;
> + page = get_zeroed_page(GFP_KERNEL);
> + if (!page)
> + return -ENOMEM;
> + if (!state->xmit.buf) {
> state->xmit.buf = (unsigned char *) page;
> uart_circ_clear(&state->xmit);
> + } else {
> + free_page(page);
> }
I see original code, but since you are adding else, does it make sense
to switch to positive condition?
> + unsigned long flags = 0;
Ditto about assignment.
--
With Best Regards,
Andy Shevchenko
next prev parent reply other threads:[~2018-07-06 16:49 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-05 0:01 [PATCH] uart: fix race between uart_put_char() and uart_shutdown() Tycho Andersen
2018-06-05 3:59 ` Serge E. Hallyn
2018-06-06 21:42 ` Tycho Andersen
2018-06-28 12:05 ` Greg Kroah-Hartman
2018-06-29 10:24 ` [PATCH v2] " Tycho Andersen
2018-06-29 16:43 ` Tycho Andersen
2018-07-06 14:39 ` Greg Kroah-Hartman
2018-07-06 16:24 ` [PATCH v3] " Tycho Andersen
2018-07-06 16:49 ` Andy Shevchenko [this message]
2018-07-06 18:39 ` Tycho Andersen
2018-07-06 20:48 ` Andy Shevchenko
2018-07-06 21:22 ` Tycho Andersen
2018-07-11 16:07 ` [PATCH v4] " Tycho Andersen
2018-07-11 19:24 ` Serge E. Hallyn
2018-07-11 19:49 ` Serge E. Hallyn
2018-07-11 20:00 ` Tycho Andersen
2018-07-12 15:05 ` Greg Kroah-Hartman
2018-07-12 9:03 ` Andy Shevchenko
2018-07-12 14:13 ` Tycho Andersen
2018-07-12 15:04 ` Greg Kroah-Hartman
2018-07-12 15:08 ` Tycho Andersen
2018-07-12 15:40 ` Greg Kroah-Hartman
2018-07-12 18:18 ` Tycho Andersen
2018-07-12 18:25 ` Greg Kroah-Hartman
2018-07-12 18:30 ` Tycho Andersen
2018-07-13 9:28 ` Greg Kroah-Hartman
2018-07-13 14:01 ` Tycho Andersen
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='CAHp75Vfbh5SzpqP=2LfeXteEGrBG46dPfeHsU0ac5SiJSjZOXw@mail.gmail.com' \
--to=andy.shevchenko@gmail.com \
--cc=gregkh@linuxfoundation.org \
--cc=jslaby@suse.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-serial@vger.kernel.org \
--cc=serge@hallyn.com \
--cc=tycho@tycho.ws \
/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).