From: Tom Zanussi <zanussi@kernel.org>
To: David Laight <David.Laight@ACULAB.COM>,
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>
Cc: Scott Wood <swood@redhat.com>
Subject: Re: [PATCH RT 21/23] sched: migrate_enable: Busy loop until the migration request is completed
Date: Thu, 05 Mar 2020 11:58:33 -0600 [thread overview]
Message-ID: <1583431113.12738.63.camel@kernel.org> (raw)
In-Reply-To: <9003e4a9e5774ecfa377d218c71c2ad2@AcuMS.aculab.com>
Hi David,
On Thu, 2020-03-05 at 13:38 +0000, David Laight wrote:
> From: zanussi@kernel.org
> > Sent: 27 February 2020 14:34
> > [ 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.
>
> What happens if the process changing the affinity mask is running
> at a higher RT priority than that of the task being changed and
> the new mask requires it run on the same cpu?
>
> David
>
This patch, 'sched: migrate_enable: Use per-cpu cpu_stop_work', removes
the busy wait and is queued for the next update:
https://lore.kernel.org/linux-rt-users/20200203173732.ldbgbpwao7xm23mm@linutronix.de/T/#mf19a8af38ac4ea0cc01775835e9d715f175f0b7b
Thanks,
Tom
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes,
> MK1 1PT, UK
> Registration No: 1397386 (Wales)
>
next prev parent reply other threads:[~2020-03-05 17:58 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
2020-03-03 21:54 ` Steven Rostedt
2020-03-05 13:38 ` David Laight
2020-03-05 17:58 ` Tom Zanussi [this message]
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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