LKML Archive on lore.kernel.org
 help / color / Atom feed
From: "Paul E. McKenney" <paulmck@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Marco Elver <elver@google.com>, Qian Cai <cai@lca.pw>,
	Will Deacon <will@kernel.org>, Ingo Molnar <mingo@redhat.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	kasan-dev <kasan-dev@googlegroups.com>
Subject: Re: [PATCH] locking/osq_lock: fix a data race in osq_wait_next
Date: Wed, 29 Jan 2020 11:26:02 -0800
Message-ID: <20200129192602.GA2935@paulmck-ThinkPad-P72> (raw)
In-Reply-To: <20200129184935.GU14879@hirez.programming.kicks-ass.net>

On Wed, Jan 29, 2020 at 07:49:35PM +0100, Peter Zijlstra wrote:
> On Tue, Jan 28, 2020 at 04:22:53PM -0800, Paul E. McKenney wrote:
> > On Tue, Jan 28, 2020 at 05:56:55PM +0100, Peter Zijlstra wrote:
> > > On Tue, Jan 28, 2020 at 12:46:26PM +0100, Marco Elver wrote:
> > > 
> > > > > Marco, any thought on improving KCSAN for this to reduce the false
> > > > > positives?
> > > > 
> > > > Define 'false positive'.
> > > 
> > > I'll use it where the code as written is correct while the tool
> > > complains about it.
> > 
> > I could be wrong, but I would guess that Marco is looking for something
> > a little less subjective and a little more specific.  ;-)
> 
> How is that either? If any valid translation by a compile results in
> correct functionality, yet the tool complains, then surely we can speak
> of a objective fact.

Marco covered my concern in his point about the need to change the
compiler.

In any case, agreed, if a read does nothing but feed into the old/new
values for a CAS, the only thing a reasonable compiler (as opposed to
a just-barely-meets-the-standard demonic compiler) can do to you is to
decrease the CAS success rate.

							Thanx, Paul

  reply index

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-22 16:38 Qian Cai
2020-01-22 16:59 ` Will Deacon
2020-01-22 17:08   ` Qian Cai
2020-01-22 22:38     ` Marco Elver
2020-01-22 23:54       ` Qian Cai
2020-01-23  9:39         ` Peter Zijlstra
2020-01-28  3:11           ` Qian Cai
2020-01-28 11:46             ` Marco Elver
2020-01-28 12:53               ` Qian Cai
2020-01-28 16:52               ` Peter Zijlstra
2020-01-28 16:56               ` Peter Zijlstra
2020-01-29  0:22                 ` Paul E. McKenney
2020-01-29 15:29                   ` Marco Elver
2020-01-29 18:40                     ` Peter Zijlstra
2020-01-30 13:39                       ` Marco Elver
2020-01-30 13:48                         ` Peter Zijlstra
2020-01-31  3:32                           ` Qian Cai
2020-01-29 18:49                   ` Peter Zijlstra
2020-01-29 19:26                     ` Paul E. McKenney [this message]
2020-01-23  9:36       ` Peter Zijlstra
2020-01-28  3:12         ` Qian Cai
2020-01-28  8:18           ` Marco Elver
2020-01-28 10:10             ` Qian Cai
2020-01-28 10:29               ` Marco Elver
2020-01-22 17:09 ` Peter Zijlstra

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=20200129192602.GA2935@paulmck-ThinkPad-P72 \
    --to=paulmck@kernel.org \
    --cc=cai@lca.pw \
    --cc=elver@google.com \
    --cc=kasan-dev@googlegroups.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mingo@redhat.com \
    --cc=peterz@infradead.org \
    --cc=will@kernel.org \
    /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