From: Andrew Morton <akpm@linux-foundation.org>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Marcelo Tosatti <mtosatti@redhat.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Minchan Kim <minchan@kernel.org>,
Matthew Wilcox <willy@infradead.org>,
Mel Gorman <mgorman@techsingularity.net>,
Nicolas Saenz Julienne <nsaenzju@redhat.com>,
Juri Lelli <juri.lelli@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
"Paul E. McKenney" <paulmck@kernel.org>,
Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Steven Rostedt <rostedt@goodmis.org>,
Daniel Bristot de Oliveira <bristot@redhat.com>
Subject: Re: [patch v5] mm: lru_cache_disable: replace work queue synchronization with synchronize_rcu
Date: Fri, 11 Mar 2022 16:40:43 -0800 [thread overview]
Message-ID: <20220311164043.e5e4f3bcac2b472792085f47@linux-foundation.org> (raw)
In-Reply-To: <YisJ5SLBijAbcwHD@linutronix.de>
On Fri, 11 Mar 2022 09:35:49 +0100 Sebastian Andrzej Siewior <bigeasy@linutronix.de> wrote:
> + sched division
>
> On 2022-03-10 18:23:26 [-0800], Andrew Morton wrote:
> > On Thu, 10 Mar 2022 10:22:12 -0300 Marcelo Tosatti <mtosatti@redhat.com> wrote:
> > > On systems that run FIFO:1 applications that busy loop,
> > > any SCHED_OTHER task that attempts to execute
> > > on such a CPU (such as work threads) will not
> > > be scheduled, which leads to system hangs.
> …
> >
> > Permitting a realtime thread to hang the entire system warrants a
> > -stable backport, I think. That's just rude.
>
> I'm not sure if someone is not willingly breaking the system. Based on
> my experience, a thread with an elevated priority (that FIFO, RR or DL)
> should not hog the CPU. A normal user (!root && !CAP_SYS_NICE) can't
> increase the priority of the task.
> To avoid a system hangup there is sched_rt_runtime_us which ensures that
> all RT threads are throttled once the RT class exceed a certain amount
> of runtime. This has been relaxed a little on systems with more CPUs so
> that the RT runtime can be shared but this sharing (RT_RUNTIME_SHARE)
> has been disabled by default a while ago. That safe switch
> (sched_rt_runtime_us) can be disabled and is usually disabled on RT
> system since the RT tasks usually run longer especially in corner cases.
Does all this apply if the kernel is non-preemptible?
Marcelo, do you know how the offending system bypassed the failsafe?
next prev parent reply other threads:[~2022-03-12 0:40 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-22 16:01 [patch v2] mm: lru_cache_disable: replace work queue synchronization with synchronize_rcu Marcelo Tosatti
2022-02-22 16:07 ` [patch v3] " Marcelo Tosatti
2022-02-22 16:25 ` Nicolas Saenz Julienne
2022-03-04 1:03 ` Andrew Morton
2022-03-04 1:49 ` Paul E. McKenney
2022-03-04 15:08 ` Marcelo Tosatti
2022-03-04 16:02 ` Paul E. McKenney
2022-03-04 15:11 ` Marcelo Tosatti
2022-03-04 16:29 ` [patch v4] " Marcelo Tosatti
2022-03-05 0:35 ` Andrew Morton
2022-03-07 18:52 ` Marcelo Tosatti
2022-03-10 13:22 ` [patch v5] " Marcelo Tosatti
2022-03-11 2:23 ` Andrew Morton
2022-03-11 8:35 ` Sebastian Andrzej Siewior
2022-03-12 0:40 ` Andrew Morton [this message]
2022-03-12 20:39 ` Marcelo Tosatti
2022-03-13 9:23 ` Hillf Danton
2022-03-31 13:52 ` Borislav Petkov
2022-04-28 18:00 ` Marcelo Tosatti
2022-05-28 21:18 ` Andrew Morton
2022-05-28 22:54 ` Michael Larabel
2022-05-29 0:48 ` Michael Larabel
2022-06-19 12:14 ` Thorsten Leemhuis
2022-06-22 0:15 ` Andrew Morton
2022-03-05 4:33 ` [patch v4] " Paul E. McKenney
2022-03-08 17:41 ` Minchan Kim
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