From: Darren Hart <dvhart@linux.intel.com>
To: Davidlohr Bueso <dave@stgolabs.net>,
"Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
"Carlos O'Donell" <carlos@redhat.com>,
Ingo Molnar <mingo@elte.hu>, Jakub Jelinek <jakub@redhat.com>,
"linux-man@vger.kernel.org" <linux-man@vger.kernel.org>,
lkml <linux-kernel@vger.kernel.org>,
Arnd Bergmann <arnd@arndb.de>,
Steven Rostedt <rostedt@goodmis.org>,
Peter Zijlstra <peterz@infradead.org>,
Linux API <linux-api@vger.kernel.org>,
Torvald Riegel <triegel@redhat.com>,
Roland McGrath <roland@redhat.com>,
Darren Hart <dvhart@infradead.org>,
Anton Blanchard <anton@samba.org>, Petr Baudis <pasky@suse.cz>,
Eric Dumazet <edumazet@google.com>,
bill o gallmeister <bgallmeister@gmail.com>,
Jan Kiszka <jan.kiszka@siemens.com>,
Daniel Wagner <wagi@monom.org>, Rich Felker <dalias@libc.org>
Subject: Re: futex(2) man page update help request
Date: Fri, 16 Jan 2015 17:11:49 -0800 [thread overview]
Message-ID: <D0DEF5CA.B7F02%dvhart@linux.intel.com> (raw)
In-Reply-To: <1421456216.27134.2.camel@stgolabs.net>
On 1/16/15, 4:56 PM, "Davidlohr Bueso" <dave@stgolabs.net> wrote:
>On Fri, 2015-01-16 at 21:54 +0100, Michael Kerrisk (man-pages) wrote:
>> On 01/16/2015 04:20 PM, Thomas Gleixner wrote:
>> > On Fri, 16 Jan 2015, Michael Kerrisk (man-pages) wrote:
>> >
>> >> Hello Thomas,
>> >>
>> >> On 01/15/2015 11:23 PM, Thomas Gleixner wrote:
>> >>> On Thu, 15 Jan 2015, Michael Kerrisk (man-pages) wrote:
>> >>>>> [EINVAL] uaddr equal uaddr2. Requeue to same futex.
>> >>>>
>> >>>> ??? I added this, but does this error not occur only for PI
>>requeues?
>> >>>
>> >>> It's equally wrong for normal futexes. And its actually the same
>>code
>> >>> checking for this for all variants.
>> >>
>> >> I don't understand "equally wrong" in your reply, I'm sorry. Do you
>> >> mean:
>> >>
>> >> a) This error text should be there for both normal and PI requeues
>> >
>> > It is there for both. The requeue code has that check independent of
>> > the requeue type (normal/pi). It never makes sense to requeue
>> > something to itself whether normal or pi futex. We added this for PI,
>> > because there it is harmful, but we did not special case it. So normal
>> > futexes get the same treatment.
>>
>> Hello Thomas,
>>
>> Color me stupid, but I can't see this in futex_requeue(). Where is that
>> check that is "independent of the requeue type (normal/pi)"?
>>
>> When I look through futex_requeue(), all the likely looking sources
>> of EINVAL are governed by a check on the 'requeue_pi' argument.
>
>Yeah, its not very straightforward, I was also scratching my head. First
>we do:
>
> if (requeue_pi) {
> /*
> * Requeue PI only works on two distinct uaddrs. This
> * check is only valid for private futexes. See below.
> */
> if (uaddr1 == uaddr2)
> return -EINVAL;
We check here to abort as early as possible for the usual security reasons.
>
>Then:
>
> /*
> * The check above which compares uaddrs is not sufficient for
> * shared futexes. We need to compare the keys:
> */
> if (requeue_pi && match_futex(&key1, &key2)) {
> ret = -EINVAL;
> goto out_put_keys;
> }
>
>I wonder why we're checking for requeue_pi again, when, at least
>according to the comments, it should be for shared. I guess it would
>make sense depending on the mappings as the keys are the only true way
>of determining if both futexes are the same, so perhaps:
>
> if ((requeue_pi || (flags & FLAGS_SHARED)) && match_futex())
No, the rule only applies to requeue_pi. This check is the for-sure
version of the uaddr comparison above. We could add if flags &
FLAGS_SHARED, but I'm not sure it's worth it.
--
Darren Hart
Intel Open Source Technology Center
next prev parent reply other threads:[~2015-01-17 1:12 UTC|newest]
Thread overview: 80+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-05-14 10:35 futex(2) man page update help request Michael Kerrisk (man-pages)
2014-05-14 16:18 ` Darren Hart
2014-05-14 19:03 ` Michael Kerrisk (man-pages)
2014-05-14 19:59 ` Darren Hart
2014-05-14 20:23 ` Carlos O'Donell
2014-05-14 20:44 ` Andy Lutomirski
2014-05-14 23:34 ` Thomas Gleixner
2014-05-15 3:12 ` Carlos O'Donell
2014-05-15 4:49 ` Michael Kerrisk (man-pages)
2014-05-15 4:53 ` Michael Kerrisk (man-pages)
2014-05-15 14:14 ` Thomas Gleixner
2014-05-15 20:19 ` Michael Kerrisk (man-pages)
2014-08-04 14:46 ` Carlos O'Donell
2014-05-15 20:35 ` Darren Hart
2015-01-15 15:12 ` Michael Kerrisk (man-pages)
2015-01-17 1:33 ` Darren Hart
2015-01-17 9:16 ` Michael Kerrisk (man-pages)
2015-01-17 19:26 ` Darren Hart
2015-01-18 10:18 ` Michael Kerrisk (man-pages)
2015-01-15 15:10 ` Michael Kerrisk (man-pages)
2015-01-15 22:23 ` Thomas Gleixner
2015-01-16 15:17 ` Michael Kerrisk (man-pages)
2015-01-16 15:20 ` Thomas Gleixner
2015-01-16 20:54 ` Michael Kerrisk (man-pages)
2015-01-17 0:46 ` Darren Hart
2015-01-19 10:45 ` Thomas Gleixner
2015-01-19 14:07 ` Michael Kerrisk (man-pages)
2015-01-23 18:19 ` Torvald Riegel
2015-01-24 10:05 ` Thomas Gleixner
2015-01-24 12:58 ` Torvald Riegel
2015-01-24 16:25 ` Thomas Gleixner
2015-01-17 0:56 ` Davidlohr Bueso
2015-01-17 1:11 ` Darren Hart [this message]
2015-01-23 18:29 ` Torvald Riegel
2015-01-24 11:35 ` Thomas Gleixner
2015-01-24 13:12 ` Torvald Riegel
2015-01-27 7:48 ` Michael Kerrisk (man-pages)
2015-02-05 19:57 ` Darren Hart
2014-05-15 8:13 ` Peter Zijlstra
2014-05-15 15:43 ` Darren Hart
2014-05-15 8:14 ` Peter Zijlstra
2014-05-15 13:18 ` Carlos O'Donell
2014-05-15 13:22 ` Peter Zijlstra
2014-05-15 13:49 ` Michael Kerrisk (man-pages)
2014-05-15 13:55 ` Peter Zijlstra
2014-05-15 14:39 ` Carlos O'Donell
2014-05-15 15:11 ` Peter Zijlstra
2014-05-14 20:56 ` Davidlohr Bueso
2014-05-14 21:03 ` Darren Hart
2014-05-14 22:21 ` Paul E. McKenney
2014-05-15 0:28 ` H. Peter Anvin
2014-05-15 0:35 ` Andy Lutomirski
2014-05-15 0:41 ` H. Peter Anvin
2014-05-15 19:10 ` Carlos O'Donell
2014-05-14 21:05 ` Davidlohr Bueso
2014-05-15 15:15 ` Joseph S. Myers
2014-05-15 0:18 ` H. Peter Anvin
2014-05-15 5:21 ` Darren Hart
2014-05-15 8:23 ` Peter Zijlstra
2014-05-15 13:46 ` Michael Kerrisk (man-pages)
2014-05-15 14:59 ` H. Peter Anvin
2014-05-15 15:42 ` chrubis
2014-05-15 15:52 ` H. Peter Anvin
2014-05-15 16:01 ` chrubis
2014-05-15 16:07 ` H. Peter Anvin
2014-05-15 16:17 ` chrubis
2014-05-15 16:56 ` H. Peter Anvin
2014-05-15 17:06 ` chrubis
2014-05-15 15:47 ` Darren Hart
2014-05-15 15:35 ` chrubis
2014-05-15 15:28 ` chrubis
2014-05-15 15:40 ` Steven Rostedt
2014-05-15 16:14 ` Darren Hart
2014-05-15 16:30 ` chrubis
2014-05-15 18:17 ` Darren Hart
2014-05-15 19:05 ` chrubis
2014-05-15 19:38 ` Darren Hart
2014-08-11 10:19 ` chrubis
2014-11-26 13:41 ` Cyril Hrubis
2015-02-16 13:14 ` Cyril Hrubis
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