mirror of https://lore.kernel.org/lkml/
 help / color / mirror / Atom feed
From: Davidlohr Bueso <dave@stgolabs.net>
To: Oleg Nesterov <oleg@redhat.com>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	Peter Zijlstra <peterz@infradead.org>,
	linux-kernel@vger.kernel.org, waiman.long@hp.com,
	raghavendra.kt@linux.vnet.ibm.com
Subject: Re: [PATCH] sched/completion: completion_done() should serialize with complete()
Date: Fri, 13 Feb 2015 13:56:22 -0800	[thread overview]
Message-ID: <1423864582.2046.82.camel@stgolabs.net> (raw)
In-Reply-To: <20150212195913.GA30430@redhat.com>

On Thu, 2015-02-12 at 20:59 +0100, Oleg Nesterov wrote:
> Commit de30ec47302c "Remove unnecessary ->wait.lock serialization when
> reading completion state" was not correct, without lock/unlock the code
> like stop_machine_from_inactive_cpu()
> 
> 	while (!completion_done())
> 		cpu_relax();
> 
> can return before complete() finishes its spin_unlock() which writes to
> this memory. And spin_unlock_wait().

How about reverting the patch altogether?

This was never a problem nor have I ever seen a performance issues in
completions that would merit these lockless checks. The commit changelog
has *zero* information, so I don't know if this was ever a real issue.

Thanks,
Davidlohr


  parent reply	other threads:[~2015-02-13 21:56 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-02-12  0:34 BUG: spinlock bad magic on CPU#0, migration/0/9 Paul E. McKenney
2015-02-12  3:15 ` Davidlohr Bueso
2015-02-12  3:43   ` Paul E. McKenney
2015-02-12 17:28   ` Oleg Nesterov
2015-02-12 17:41     ` Oleg Nesterov
2015-02-12 17:58       ` Davidlohr Bueso
2015-02-12 19:10       ` Nicholas Mc Guire
2015-02-12 19:37         ` Oleg Nesterov
2015-02-12 21:27           ` Oleg Nesterov
2015-02-13 18:17             ` Nicholas Mc Guire
2015-02-13 18:53               ` Oleg Nesterov
2015-02-14  8:35                 ` Nicholas Mc Guire
2015-02-14 14:00                   ` Oleg Nesterov
2015-02-12 19:59         ` Davidlohr Bueso
2015-02-12 19:32       ` Nicholas Mc Guire
2015-02-12 19:39         ` Oleg Nesterov
2015-02-12 19:59 ` [PATCH] sched/completion: completion_done() should serialize with complete() Oleg Nesterov
2015-02-13 21:09   ` Paul E. McKenney
2015-02-13 21:56   ` Davidlohr Bueso [this message]
2015-02-13 22:02     ` Davidlohr Bueso
2015-02-16  8:21   ` Peter Zijlstra
2015-02-16 16:51     ` Oleg Nesterov
2015-02-18 17:06   ` [tip:sched/core] sched/completion: Serialize completion_done() " tip-bot for Oleg Nesterov

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=1423864582.2046.82.camel@stgolabs.net \
    --to=dave@stgolabs.net \
    --cc=linux-kernel@vger.kernel.org \
    --cc=oleg@redhat.com \
    --cc=paulmck@linux.vnet.ibm.com \
    --cc=peterz@infradead.org \
    --cc=raghavendra.kt@linux.vnet.ibm.com \
    --cc=waiman.long@hp.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
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox
Powered by JetHome