From: Peter Zijlstra <peterz@infradead.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: mingo@kernel.org, juri.lelli@arm.com, rostedt@goodmis.org,
xlpang@redhat.com, bigeasy@linutronix.de,
linux-kernel@vger.kernel.org, mathieu.desnoyers@efficios.com,
jdesfossez@efficios.com, bristot@redhat.com
Subject: Re: [RFC][PATCH 4/4] futex: Rewrite FUTEX_UNLOCK_PI
Date: Thu, 24 Nov 2016 17:52:41 +0100 [thread overview]
Message-ID: <20161124165241.GF3174@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20161123192005.GA3107@twins.programming.kicks-ass.net>
On Wed, Nov 23, 2016 at 08:20:05PM +0100, Peter Zijlstra wrote:
> > + if (oldowner == &init_task && uval != 0) {
> > + raw_spin_lock(&pi_state->owner->pi_lock);
> > + list_del_init(&pi_state->list);
> > + raw_spin_unlock(&pi_state->owner->pi_lock);
> > + pi_state->owner = NULL;
> > + return -EAGAIN;
> > @@ -2679,6 +2690,10 @@ static int futex_lock_pi(u32 __user *uad
> >
> > out_put_key:
> > put_futex_key(&q.key);
> > +
> > + if (ret == -EAGAIN)
> > + goto retry;
> > +
>
> And this is far too clever and really needs a comment. So the crucial
> point is that this is after unqueue_me_pi(), which drops the pi_state
> and loops back to lookup the pi_state again, which, hopefully, has now
> been completely destroyed -- and therefore we hit the regular
> attach_to_pi_owner() path, fixing up our 'funny' state.
>
I'm stumped on REQUEUE_PI.. this relies on attach_to_pi_owner() and
fixup_owner() being in the same function. But this is not the case for
requeue. WAIT_REQUEUE has the fixup, as its return path finds it has
acquired the outer pi-futex (uaddr2), but the lookup_pi_state() stuff is
done by CMP_REQUEUE, which does the actual transfer of the waiters from
inner futex (uaddr1) to outer futex (uaddr2).
Maybe I can restructure things a bit, I think CMP_REQUEUE would also
know who actually acquired the outer-futex, but I have to think more on
this and the brain is pretty fried...
next prev parent reply other threads:[~2016-11-24 16:52 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-10-03 9:12 [RFC][PATCH 0/4] FUTEX_UNLOCK_PI wobbles Peter Zijlstra
2016-10-03 9:12 ` [RFC][PATCH 1/4] futex: Cleanup variable names for futex_top_waiter() Peter Zijlstra
2016-10-03 14:15 ` Steven Rostedt
2016-10-05 3:58 ` Davidlohr Bueso
2016-10-03 9:12 ` [RFC][PATCH 2/4] futex: Use smp_store_release() in mark_wake_futex() Peter Zijlstra
2016-10-03 14:19 ` Steven Rostedt
2016-10-05 3:57 ` Davidlohr Bueso
2016-10-05 6:20 ` Peter Zijlstra
2016-10-03 9:12 ` [RFC][PATCH 3/4] futex: Remove rt_mutex_deadlock_account_*() Peter Zijlstra
2016-10-03 9:34 ` Peter Zijlstra
2016-10-03 14:25 ` Steven Rostedt
2016-10-05 1:08 ` Davidlohr Bueso
2016-10-05 7:29 ` Sebastian Andrzej Siewior
2016-10-03 9:12 ` [RFC][PATCH 4/4] futex: Rewrite FUTEX_UNLOCK_PI Peter Zijlstra
2016-10-03 15:36 ` Steven Rostedt
2016-10-03 15:44 ` Peter Zijlstra
2016-10-03 15:45 ` Peter Zijlstra
2016-10-03 16:23 ` Steven Rostedt
2016-10-05 7:41 ` Sebastian Andrzej Siewior
2016-10-05 8:09 ` Peter Zijlstra
2016-10-05 8:21 ` Sebastian Andrzej Siewior
2016-10-05 8:32 ` Peter Zijlstra
2016-10-06 10:29 ` Peter Zijlstra
2016-10-07 11:21 ` Peter Zijlstra
2016-10-08 15:53 ` Thomas Gleixner
2016-10-08 16:55 ` Peter Zijlstra
2016-10-08 17:06 ` Thomas Gleixner
2016-10-10 10:17 ` Thomas Gleixner
2016-10-10 11:40 ` Peter Zijlstra
2016-10-21 12:27 ` Peter Zijlstra
2016-10-27 20:36 ` Thomas Gleixner
2016-11-23 19:20 ` Peter Zijlstra
2016-11-24 16:52 ` Peter Zijlstra [this message]
2016-11-24 17:56 ` Thomas Gleixner
2016-11-24 18:58 ` Peter Zijlstra
2016-11-25 9:23 ` Peter Zijlstra
2016-11-25 10:03 ` Peter Zijlstra
2016-11-25 19:13 ` Thomas Gleixner
2016-11-25 14:09 ` Peter Zijlstra
2016-10-08 18:22 ` Thomas Gleixner
2016-10-09 11:17 ` Thomas Gleixner
2016-10-10 14:06 ` Peter Zijlstra
2016-10-05 1:02 ` [RFC][PATCH 0/4] FUTEX_UNLOCK_PI wobbles Davidlohr Bueso
2016-10-05 6:20 ` Peter Zijlstra
2016-10-05 7:26 ` Sebastian Andrzej Siewior
2016-10-05 16:04 ` Davidlohr Bueso
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=20161124165241.GF3174@twins.programming.kicks-ass.net \
--to=peterz@infradead.org \
--cc=bigeasy@linutronix.de \
--cc=bristot@redhat.com \
--cc=jdesfossez@efficios.com \
--cc=juri.lelli@arm.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mathieu.desnoyers@efficios.com \
--cc=mingo@kernel.org \
--cc=rostedt@goodmis.org \
--cc=tglx@linutronix.de \
--cc=xlpang@redhat.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).