From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Joe Korty <joe.korty@concurrent-rt.com>
Cc: Julia Cartwright <julia@ni.com>,
tglx@linutronix.de, rostedt@goodmis.org,
linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org,
Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH RT v2] sched/migrate_disable: fallback to preempt_disable() instead barrier()
Date: Wed, 11 Jul 2018 17:39:52 +0200 [thread overview]
Message-ID: <20180711153952.2fcniletg62hy7xf@linutronix.de> (raw)
In-Reply-To: <20180706105857.5tgi5irdxdryet64@linutronix.de>
On 2018-07-06 12:58:57 [+0200], To Joe Korty wrote:
> On SMP + !RT migrate_disable() is still around. It is not part of spin_lock()
> anymore so it has almost no users. However the futex code has a workaround for
> the !in_atomic() part of migrate disable which fails because the matching
> migrade_disable() is no longer part of spin_lock().
>
> On !SMP + !RT migrate_disable() is reduced to barrier(). This is not optimal
> because we few spots where a "preempt_disable()" statement was replaced with
> "migrate_disable()".
>
> We also used the migration_disable counter to figure out if a sleeping lock is
> acquired so RCU does not complain about schedule() during rcu_read_lock() while
> a sleeping lock is held. This changed, we no longer use it, we have now a
> sleeping_lock counter for the RCU purpose.
>
> This means we can now:
> - for SMP + RT_BASE
> full migration program, nothing changes here
>
> - for !SMP + RT_BASE
> the migration counting is no longer required. It used to ensure that the task
> is not migrated to another CPU and that this CPU remains online. !SMP ensures
> that already.
> Move it to CONFIG_SCHED_DEBUG so the counting is done for debugging purpose
> only.
>
> - for all other cases including !RT
> fallback to preempt_disable(). The only remaining users of migrate_disable()
> are those which were converted from preempt_disable() and the futex
> workaround which is already in the preempt_disable() section due to the
> spin_lock that is held.
>
> Cc: stable-rt@vger.kernel.org
> Reported-by: joe.korty@concurrent-rt.com
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> ---
> v1…v2: limit migrate_disable to RT only. Use preempt_disable() for !RT
> if migrate_disable() is used.
If there are no objections I would pick this up for next v4.16.
Sebastian
next prev parent reply other threads:[~2018-07-11 15:40 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-04 17:35 [PATCH RT] sample fix for splat in futex_[un]lock_pi for !rt joe.korty
2018-07-05 15:50 ` [PATCH RT] sched/migrate_disable: fallback to preempt_disable() instead barrier() Sebastian Andrzej Siewior
2018-07-05 16:18 ` joe.korty
2018-07-05 16:59 ` Sebastian Andrzej Siewior
2018-07-06 10:58 ` [PATCH RT v2] " Sebastian Andrzej Siewior
2018-07-06 19:05 ` joe.korty
2018-07-11 15:39 ` Sebastian Andrzej Siewior [this message]
2018-07-11 15:43 ` Steven Rostedt
2018-07-05 16:23 ` [PATCH RT] " Steven Rostedt
2018-07-05 16:38 ` Sebastian Andrzej Siewior
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