From: "Paul E. McKenney" <paulmck@kernel.org>
To: Jonas Oberhauser <jonas.oberhauser@huaweicloud.com>
Cc: Alan Stern <stern@rowland.harvard.edu>,
parri.andrea@gmail.com, will@kernel.org, peterz@infradead.org,
boqun.feng@gmail.com, npiggin@gmail.com, dhowells@redhat.com,
j.alglave@ucl.ac.uk, luc.maranget@inria.fr, akiyks@gmail.com,
dlustig@nvidia.com, joel@joelfernandes.org, urezki@gmail.com,
quic_neeraju@quicinc.com, frederic@kernel.org,
linux-kernel@vger.kernel.org, lkmm@lists.linux.dev,
hernan.poncedeleon@huaweicloud.com
Subject: Re: [RFC] tools/memory-model: Rule out OOTA
Date: Thu, 16 Jan 2025 11:39:32 -0800 [thread overview]
Message-ID: <4411cf20-f889-4fd7-9e03-14744deaaf72@paulmck-laptop> (raw)
In-Reply-To: <446d6a64-7ee4-494a-bbfe-dbfdb6959f9c@huaweicloud.com>
On Thu, Jan 16, 2025 at 08:28:06PM +0100, Jonas Oberhauser wrote:
>
>
> Am 1/16/2025 um 7:40 PM schrieb Paul E. McKenney:
> > o If a value is read in the seqlock reader and used
> > across a "you need to retry" indication, that
> > flags a seqlock data race.
>
>
> This too is insufficient, you also need to prevent dereferencing or having
> control dependency inside the seqlock. Otherwise you could derefence a torn
> pointer and...
True, but isn't that prohibition separable from the underlying
implementation?
> At this point your definition of data race becomes pretty much the same as
> we have.
>
> https://github.com/open-s4c/libvsync/blob/main/vmm/vmm.cat#L150
>
>
> (also this rule should only concern reads that are actually "data-racy" - if
> the read is synchronized by some other writes, then you can read & use it
> just fine across the seqlock data race)
Perhaps LKMM should adopt this or something similar, but what do others
think?
> I also noticed that in my previous e-mail I had overlooked the reads inside
> the CS in the failure case, but you are of course right, there needs to be
> some mechanism to prevent them from being data racy unless abused.
>
> But I am not sure how to formalize that in a way that is simpler than just
> re-defining data races in general, without adding some special support to
> herd7 for it.
>
> What do you think?
I was thinking in terms of identifying reads in critical sections (sort
of like LKMM does for RCU read-side critical sections), then identifying
any dependencies from those reads that cross a failed reader boundary.
If that set is non-empty, flag it.
But I clearly cannot claim to have thought this through. ;-)
Thanx, Paul
next prev parent reply other threads:[~2025-01-16 19:39 UTC|newest]
Thread overview: 59+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-01-06 21:40 [RFC] tools/memory-model: Rule out OOTA Jonas Oberhauser
2025-01-07 10:06 ` Peter Zijlstra
2025-01-07 11:02 ` Jonas Oberhauser
2025-01-07 15:46 ` Jonas Oberhauser
2025-01-07 16:09 ` Alan Stern
2025-01-07 18:47 ` Paul E. McKenney
2025-01-08 17:39 ` Jonas Oberhauser
2025-01-08 18:09 ` Paul E. McKenney
2025-01-08 19:17 ` Jonas Oberhauser
2025-01-09 17:54 ` Paul E. McKenney
2025-01-09 18:35 ` Jonas Oberhauser
2025-01-10 14:54 ` Paul E. McKenney
2025-01-10 16:21 ` Jonas Oberhauser
2025-01-13 22:04 ` Paul E. McKenney
2025-01-16 18:40 ` Paul E. McKenney
2025-01-16 19:13 ` Jonas Oberhauser
2025-01-16 19:31 ` Paul E. McKenney
2025-01-16 20:21 ` Jonas Oberhauser
2025-01-16 19:28 ` Jonas Oberhauser
2025-01-16 19:39 ` Paul E. McKenney [this message]
2025-01-17 12:08 ` Jonas Oberhauser
2025-01-16 19:08 ` Jonas Oberhauser
2025-01-16 23:02 ` Alan Stern
2025-01-17 8:34 ` Hernan Ponce de Leon
2025-01-17 11:29 ` Jonas Oberhauser
2025-01-17 20:01 ` Alan Stern
2025-01-21 10:36 ` Jonas Oberhauser
2025-01-21 16:39 ` Alan Stern
2025-01-22 3:46 ` Jonas Oberhauser
2025-01-22 19:11 ` Alan Stern
2025-01-17 15:52 ` Alan Stern
2025-01-17 16:45 ` Jonas Oberhauser
2025-01-17 19:02 ` Alan Stern
2025-01-09 20:37 ` Peter Zijlstra
2025-01-09 21:13 ` Paul E. McKenney
2025-01-08 17:33 ` Jonas Oberhauser
2025-01-08 18:47 ` Alan Stern
2025-01-08 19:22 ` Jonas Oberhauser
2025-01-09 16:17 ` Alan Stern
2025-01-09 16:44 ` Jonas Oberhauser
2025-01-09 19:27 ` Alan Stern
2025-01-09 20:09 ` Jonas Oberhauser
2025-01-10 3:12 ` Alan Stern
2025-01-10 12:21 ` Jonas Oberhauser
2025-01-10 21:51 ` Alan Stern
2025-01-11 12:46 ` Jonas Oberhauser
2025-01-11 21:19 ` Alan Stern
2025-01-12 15:55 ` Jonas Oberhauser
2025-01-13 19:43 ` Alan Stern
2025-07-23 0:43 ` Paul E. McKenney
2025-07-23 7:26 ` Hernan Ponce de Leon
2025-07-23 16:39 ` Paul E. McKenney
2025-07-24 14:14 ` Paul E. McKenney
2025-07-25 5:23 ` Hernan Ponce de Leon
2025-07-29 20:34 ` Paul E. McKenney
2025-07-23 17:13 ` Alan Stern
2025-07-23 17:27 ` Paul E. McKenney
2025-07-23 19:25 ` Alan Stern
2025-07-23 19:57 ` Paul E. McKenney
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