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From: Scott Wood <swood@redhat.com>
To: Tom Zanussi <zanussi@kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-rt-users <linux-rt-users@vger.kernel.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Carsten Emde <C.Emde@osadl.org>, John Kacur <jkacur@redhat.com>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	Daniel Wagner <wagi@monom.org>
Subject: Re: [PATCH RT 21/23] sched: migrate_enable: Busy loop until the migration request is completed
Date: Tue, 03 Mar 2020 15:19:23 -0600	[thread overview]
Message-ID: <f783406c0254a3b36ab1123402a7b2f26f6d5699.camel@redhat.com> (raw)
In-Reply-To: <1583267977.12738.53.camel@kernel.org>

On Tue, 2020-03-03 at 14:39 -0600, Tom Zanussi wrote:
> Hi Scott,
> 
> On Tue, 2020-03-03 at 13:56 -0600, Scott Wood wrote:
> > On Thu, 2020-02-27 at 08:33 -0600, zanussi@kernel.org wrote:
> > > From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> > > 
> > > v4.14.170-rt75-rc2 stable review patch.
> > > If anyone has any objections, please let me know.
> > > 
> > > -----------
> > > 
> > > 
> > > [ Upstream commit 140d7f54a5fff02898d2ca9802b39548bf7455f1 ]
> > > 
> > > If user task changes the CPU affinity mask of a running task it
> > > will
> > > dispatch migration request if the current CPU is no longer allowed.
> > > This
> > > might happen shortly before a task enters a migrate_disable()
> > > section.
> > > Upon leaving the migrate_disable() section, the task will notice
> > > that
> > > the current CPU is no longer allowed and will will dispatch its own
> > > migration request to move it off the current CPU.
> > > While invoking __schedule() the first migration request will be
> > > processed and the task returns on the "new" CPU with "arg.done =
> > > 0". Its
> > > own migration request will be processed shortly after and will
> > > result in
> > > memory corruption if the stack memory, designed for request, was
> > > used
> > > otherwise in the meantime.
> > > 
> > > Spin until the migration request has been processed if it was
> > > accepted.
> > > 
> > > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> > > Signed-off-by: Tom Zanussi <zanussi@kernel.org>
> > > ---
> > >  kernel/sched/core.c | 7 +++++--
> > >  1 file changed, 5 insertions(+), 2 deletions(-)
> > 
> > As I said in https://marc.info/?l=linux-rt-users&m=158258256415340&w=
> > 2 if
> > you take thhis you should take the followup 2dcd94b443c5dcbc ("sched:
> > migrate_enable: Use per-cpu cpu_stop_work")
> > 
> 
> Yes, I didn't forget about this, it's just that I can't apply this to
> 4.14-rt until 4.19-rt does, otherwise it will be seen as a regression
> to someone moving from 4.14-rt to 4.19-rt.
> 
> I will be keeping my eye out for when that happens and will apply it to
> the next backport release at that point.
> 
> Thanks for making sure it wasn't missed in any case.

Steven, any plans to merge that patch into 4.19-rt?

In the meantime, I guess it's a question of whether the bug fixed by patch
18/23 is worse than the (probably quite hard to hit) deadlock addressed by
2dcd94b443c5dcbc.

-Scott



  reply	other threads:[~2020-03-03 21:19 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-27 14:33 [PATCH RT 00/23] Linux v4.14.170-rt75-rc2 zanussi
2020-02-27 14:33 ` [PATCH RT 01/23] Fix wrong-variable use in irq_set_affinity_notifier zanussi
2020-02-27 14:33 ` [PATCH RT 02/23] i2c: exynos5: Remove IRQF_ONESHOT zanussi
2020-02-27 14:33 ` [PATCH RT 03/23] i2c: hix5hd2: " zanussi
2020-02-27 14:33 ` [PATCH RT 04/23] x86: preempt: Check preemption level before looking at lazy-preempt zanussi
2020-02-27 14:33 ` [PATCH RT 05/23] sched: migrate_dis/enable: Use sleeping_lock…() to annotate sleeping points zanussi
2020-02-27 14:33 ` [PATCH RT 06/23] sched: __set_cpus_allowed_ptr: Check cpus_mask, not cpus_ptr zanussi
2020-02-27 14:33 ` [PATCH RT 07/23] sched: Remove dead __migrate_disabled() check zanussi
2020-02-27 14:33 ` [PATCH RT 08/23] sched: migrate disable: Protect cpus_ptr with lock zanussi
2020-02-27 14:33 ` [PATCH RT 09/23] lib/smp_processor_id: Don't use cpumask_equal() zanussi
2020-02-27 14:33 ` [PATCH RT 10/23] futex: Make the futex_hash_bucket spinlock_t again and bring back its old state zanussi
2020-02-27 14:33 ` [PATCH RT 11/23] locking/rtmutex: Clean ->pi_blocked_on in the error case zanussi
2020-02-27 14:33 ` [PATCH RT 12/23] lib/ubsan: Don't seralize UBSAN report zanussi
2020-02-27 14:33 ` [PATCH RT 13/23] kmemleak: Change the lock of kmemleak_object to raw_spinlock_t zanussi
2020-02-27 14:33 ` [PATCH RT 14/23] Revert "ARM: Initialize split page table locks for vector page" zanussi
2020-02-27 14:33 ` [PATCH RT 15/23] locking: Make spinlock_t and rwlock_t a RCU section on RT zanussi
2020-02-27 14:33 ` [PATCH RT 16/23] sched: migrate_enable: Use select_fallback_rq() zanussi
2020-02-27 14:33 ` [PATCH RT 17/23] sched: Lazy migrate_disable processing zanussi
2020-02-27 14:33 ` [PATCH RT 18/23] sched: migrate_enable: Use stop_one_cpu_nowait() zanussi
2020-02-27 14:33 ` [PATCH RT 19/23] sched/core: migrate_enable() must access takedown_cpu_task on !HOTPLUG_CPU zanussi
2020-02-27 14:33 ` [PATCH RT 20/23] lib/smp_processor_id: Adjust check_preemption_disabled() zanussi
2020-02-27 14:33 ` [PATCH RT 21/23] sched: migrate_enable: Busy loop until the migration request is completed zanussi
2020-03-03 19:56   ` Scott Wood
2020-03-03 20:39     ` Tom Zanussi
2020-03-03 21:19       ` Scott Wood [this message]
2020-03-03 21:54         ` Steven Rostedt
2020-03-05 13:38   ` David Laight
2020-03-05 17:58     ` Tom Zanussi
2020-02-27 14:33 ` [PATCH RT 22/23] sched/deadline: Ensure inactive_timer runs in hardirq context zanussi
2020-02-27 14:33 ` [PATCH RT 23/23] Linux 4.14.170-rt75-rc2 zanussi

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