Re: [PATCH v2] tty: fix data race in flush_to_ldisc

From: Dmitry Vyukov <dvyukov@google.com>
To: Peter Hurley <peter@hurleysoftware.com>
Cc: Greg KH <gregkh@linuxfoundation.org>,
	Jiri Slaby <jslaby@suse.com>,
	Linux kernel mailing list <linux-kernel@vger.kernel.org>,
	Jiri Slaby <jslaby@suse.cz>,
	Andrey Konovalov <andreyknvl@google.com>,
	Kostya Serebryany <kcc@google.com>,
	Alexander Potapenko <glider@google.com>,
	Paul McKenney <paulmck@linux.vnet.ibm.com>,
	Hans Boehm <hboehm@google.com>
Subject: Re: [PATCH v2] tty: fix data race in flush_to_ldisc
Date: Thu, 17 Sep 2015 15:21:02 +0200	[thread overview]
Message-ID: <CACT4Y+YsCqL3wwEPAw3cfug+HQL9+=6_kZmx-hxfxph-u1_w1Q@mail.gmail.com> (raw)
In-Reply-To: <CAKU3ayVt3Jb3tH8Mq3udM7VpChhN_v1s0-h8E66rdj4u6QcOBg@mail.gmail.com>

On Thu, Sep 17, 2015 at 3:18 PM, Peter Hurley <peter@hurleysoftware.com> wrote:
> On Thu, Sep 17, 2015 at 8:53 AM, Greg KH <gregkh@linuxfoundation.org> wrote:
>> On Thu, Sep 17, 2015 at 12:39:36PM +0200, Dmitry Vyukov wrote:
>>> flush_to_ldisc reads port->itty and checks that it is not NULL,
>>> concurrently release_tty sets port->itty to NULL. It is possible
>>> that flush_to_ldisc loads port->itty once, ensures that it is
>>> not NULL, but then reloads it again and uses. The second load
>>> can already return NULL, which will cause a crash.
>>>
>>> Use READ_ONCE to read port->itty.
>>>
>>> The data race was found with KernelThreadSanitizer (KTSAN).
>>>
>>> Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
>>
>> You sent 3 patches here, but no hint as to what order they need to be
>> applied in.  Please resend them as a patch series (i.e. 1/3, 2/3, 3/3)
>> so they can be applied correctly.
>
> Greg,
>
> I don't think these 3 patches are dependent on each other; I think they
> can be applied in any order.

Yes, these patches are independent and can be applied in any order,
and any subset of them can be applied.
I can send them as patch series if necessary, though.

-- 
Dmitry Vyukov, Software Engineer, dvyukov@google.com
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