LKML Archive on lore.kernel.org
 help / color / Atom feed
From: Thomas Gleixner <tglx@linutronix.de>
To: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
Cc: Dave Hansen <dave@sr71.net>, Borislav Petkov <bp@alien8.de>,
	LKML <linux-kernel@vger.kernel.org>,
	Dave Jones <davej@redhat.com>,
	dhillf@gmail.com, Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@kernel.org>
Subject: Re: [PATCH] kthread: Prevent unpark race which puts threads on the wrong cpu
Date: Thu, 11 Apr 2013 15:46:45 +0200 (CEST)
Message-ID: <alpine.LFD.2.02.1304111545120.21884@ionos> (raw)
In-Reply-To: <51669510.2040200@linux.vnet.ibm.com>

On Thu, 11 Apr 2013, Srivatsa S. Bhat wrote:
> The reason why we can't get rid of the bind in the unpark code is because,
> the threads are parked during CPU offline *after* calling CPU_DOWN_PREPARE.
> And during CPU_DOWN_PREPARE, the scheduler removes the CPU from the cpu_active_mask.
> So on any subsequent wakeup of these threads before they are parked, the scheduler
> will force migrate them to some other CPU (but alas it wont print this event
> because of the p->mm != NULL check in select_fallback_rq()). So during unpark
> during the next online operation we need to bind it again. But that's fine, IMHO.

No, it's not fine. If we do not have TASK_PARKED a wakeup which
happens after onlining the task and races with the unpark code will
cause the task to end up on the wrong CPU. Borislav showed traces
which prove that with ksoftirqd. So no, TASK_PARKED is going to stay.

Thanks,

	tglx

  parent reply index

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-04-05 21:43 kernel BUG at kernel/smpboot.c:134! Dave Hansen
2013-04-06  7:12 ` Srivatsa S. Bhat
2013-04-06  8:31   ` Thomas Gleixner
2013-04-07  9:20     ` Thomas Gleixner
2013-04-07  9:50       ` Borislav Petkov
2013-04-08  9:24         ` Thomas Gleixner
2013-04-08 11:55           ` Borislav Petkov
2013-04-08 12:17             ` Thomas Gleixner
2013-04-09 14:38               ` [PATCH] kthread: Prevent unpark race which puts threads on the wrong cpu Thomas Gleixner
2013-04-09 15:55                 ` Dave Hansen
2013-04-09 18:43                   ` Thomas Gleixner
2013-04-09 19:30                     ` Thomas Gleixner
2013-04-09 20:38                       ` Dave Hansen
2013-04-09 20:54                         ` Dave Hansen
2013-04-10  8:29                         ` Thomas Gleixner
2013-04-10 10:51                           ` Thomas Gleixner
2013-04-10 19:41                             ` Dave Hansen
2013-04-11 10:19                               ` Thomas Gleixner
2013-04-11 10:48                                 ` Srivatsa S. Bhat
2013-04-11 11:43                                   ` Srivatsa S. Bhat
2013-04-11 11:59                                     ` Srivatsa S. Bhat
2013-04-11 12:51                                     ` Thomas Gleixner
2013-04-11 12:54                                     ` Thomas Gleixner
2013-04-11 13:46                                   ` Thomas Gleixner [this message]
2013-04-11 18:07                                 ` Dave Hansen
2013-04-11 19:48                                   ` Thomas Gleixner
2013-04-10 14:03                   ` [PATCH] CPU hotplug, smpboot: Fix crash in smpboot_thread_fn() Srivatsa S. Bhat
2013-04-11  8:10                     ` Thomas Gleixner
2013-04-11 10:19                       ` Srivatsa S. Bhat
2013-04-11 19:16                 ` [PATCH] kthread: Prevent unpark race which puts threads on the wrong cpu Srivatsa S. Bhat
2013-04-11 20:47                   ` Thomas Gleixner
2013-04-11 21:19                     ` Srivatsa S. Bhat
2013-04-12 10:59                       ` Thomas Gleixner
2013-04-12 11:26                         ` Srivatsa S. Bhat
2013-04-15 19:49                         ` Dave Hansen
2013-04-12 10:41                 ` Peter Zijlstra
2013-04-12 12:32                 ` [tip:core/urgent] " tip-bot for Thomas Gleixner

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=alpine.LFD.2.02.1304111545120.21884@ionos \
    --to=tglx@linutronix.de \
    --cc=bp@alien8.de \
    --cc=dave@sr71.net \
    --cc=davej@redhat.com \
    --cc=dhillf@gmail.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mingo@kernel.org \
    --cc=peterz@infradead.org \
    --cc=srivatsa.bhat@linux.vnet.ibm.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

LKML Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/lkml/0 lkml/git/0.git
	git clone --mirror https://lore.kernel.org/lkml/1 lkml/git/1.git
	git clone --mirror https://lore.kernel.org/lkml/2 lkml/git/2.git
	git clone --mirror https://lore.kernel.org/lkml/3 lkml/git/3.git
	git clone --mirror https://lore.kernel.org/lkml/4 lkml/git/4.git
	git clone --mirror https://lore.kernel.org/lkml/5 lkml/git/5.git
	git clone --mirror https://lore.kernel.org/lkml/6 lkml/git/6.git
	git clone --mirror https://lore.kernel.org/lkml/7 lkml/git/7.git
	git clone --mirror https://lore.kernel.org/lkml/8 lkml/git/8.git
	git clone --mirror https://lore.kernel.org/lkml/9 lkml/git/9.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 lkml lkml/ https://lore.kernel.org/lkml \
		linux-kernel@vger.kernel.org
	public-inbox-index lkml

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-kernel


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git