Re: seqcount usage in xt_replace_table()

From: Andrea Parri <andrea.parri@amarulasolutions.com>
To: Dmitry Vyukov <dvyukov@google.com>
Cc: Anatol Pomozov <anatol.pomozov@gmail.com>,
	Florian Westphal <fw@strlen.de>,
	Paul McKenney <paulmck@linux.ibm.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Andrey Konovalov <andreyknvl@google.com>,
	Alan Stern <stern@rowland.harvard.edu>,
	Luc Maranget <luc.maranget@inria.fr>,
	Will Deacon <will.deacon@arm.com>,
	Peter Zijlstra <peterz@infradead.org>
Subject: Re: seqcount usage in xt_replace_table()
Date: Wed, 9 Jan 2019 13:11:26 +0100	[thread overview]
Message-ID: <20190109121126.GA7141@andrea> (raw)
In-Reply-To: <CACT4Y+YAr1XuwAy1qRL678VHZjzsbAQ05o1zoN9ZfC0muYzK8g@mail.gmail.com>

On Wed, Jan 09, 2019 at 12:55:27PM +0100, Dmitry Vyukov wrote:
> On Wed, Jan 9, 2019 at 12:24 PM Andrea Parri
> <andrea.parri@amarulasolutions.com> wrote:
> >
> > On Tue, Jan 08, 2019 at 04:36:46PM -0800, Anatol Pomozov wrote:
> > > Hello
> > >
> > > On Tue, Jan 8, 2019 at 4:02 PM Andrea Parri
> > > <andrea.parri@amarulasolutions.com> wrote:
> > > >
> > > > Hi Anatol,
> > > >
> > > > On Tue, Jan 08, 2019 at 11:33:39AM -0800, Anatol Pomozov wrote:
> > > > > Hello folks,
> > > > >
> > > > > A bit of context what I am doing. I am trying to port KTSAN (Kernel
> > > > > Thread Sanitizer) tool to v4.20. That tool tracks shared data usage
> > > > > and makes sure it is accessed in a thread-safe manner.
> > > >
> > > > Interesting!  FYI, some LKMM's maintainers (Paul included) had and
> > > > continued to have some "fun" discussing topics related to "thread-
> > > > safe memory accesses": I'm sure that they'll be very interested in
> > > > such work of yours and eager to discuss your results.
> > >
> > > Thread Sanitizer is a great tool to find thread-safety issues with
> > > user-space code. The tool been developed by a team of smart people
> > > from Google [1].
> > >
> > > KTSAN is an attempt to bring the same ideas to Linux kernel [2]. A
> > > bunch of work been done there but the project is still at
> > > proof-of-concept point.
> >
> > Yes, I have been aware of these tools since at least  ;-)
> >
> >   https://groups.google.com/forum/#!msg/ktsan/bVZ1c6H2NE0/Dxrw55bfBAAJ
> >
> >
> > >
> > > I am not a part of Google's dynamic tools team. But I've decided to
> > > pick something to do during the New Year holidays so started porting
> > > KTSAN from v4.2 to v4.20. The work is "almost completed" but I need to
> > > fix a few crashes [3].
> >
> > I guess my first reaction would remain
> >
> >   "it's kind of hard (to use an euphemism) to review 7,582 additions
> >   or so for a data race detector without a clear/an accepted (by the
> >   community) notion of data race..."
> 
> Tsan's notion of a data race is basically the C/C++'s notion:
> concurrent/unsynchronized non-atomic access in different threads at
> least one of which is a write.

Yeah, I think that this notion needs to be detailed, discussed,
documented, and discussed again. ;-)

> Tremendous (for such a project) benefits of automatic data race
> detection is a good motivation to finally agree on and accept a
> practically useful notion of a data race.

Agreed.

  Andrea