From: Andrea Parri <andrea.parri@amarulasolutions.com>
To: Dmitry Vyukov <dvyukov@google.com>
Cc: "Paul E. McKenney" <paulmck@linux.ibm.com>,
Anatol Pomozov <anatol.pomozov@gmail.com>,
Florian Westphal <fw@strlen.de>,
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: Thu, 10 Jan 2019 13:30:08 +0100 [thread overview]
Message-ID: <20190110123008.GA13625@andrea> (raw)
In-Reply-To: <CACT4Y+ZZYxE5z4_wZ_Na3z6Y-RmhfrHt3y3sQzUcdUuR35Xc_g@mail.gmail.com>
> For seqcounts we currently simply ignore all accesses within the read
> section (thus the requirement to dynamically track read sections).
> What does LKMM say about seqlocks?
LKMM does not currently model seqlocks, if that's what you're asking;
c.f., tools/memory-model/linux-kernel.def for a list of the currently
supported synchronization primitives.
LKMM has also no notion of "data race", it insists that the code must
contain no unmarked accesses; we have been discussing such extensions
since at least Dec'17 (we're not quite there!, as mentioned by Paul).
My opinion is that ignoring all accesses within a given read section
_can_ lead to false negatives (in every possible definition of "data
race" and "read sections" I can think of at the moment ;D):
P0 P1
read_seqbegin() x = 1;
r0 = x;
read_seqretry() // =0
ought to be "racy"..., right? (I didn't audit all the callsites for
read_{seqbegin,seqretry}(), but I wouldn't be surprised to find such
pattern ;D ... "legacy", as you recalled).
Andrea
next prev parent reply other threads:[~2019-01-10 12:30 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-08 19:33 seqcount usage in xt_replace_table() Anatol Pomozov
2019-01-08 22:37 ` Florian Westphal
2019-01-10 12:41 ` Peter Zijlstra
2019-01-10 12:53 ` Dmitry Vyukov
2019-01-10 20:18 ` Peter Zijlstra
2019-01-10 14:48 ` Florian Westphal
2019-01-10 20:20 ` Peter Zijlstra
2019-01-10 20:25 ` Peter Zijlstra
2019-01-10 22:29 ` Florian Westphal
2019-01-11 8:34 ` Peter Zijlstra
2019-01-11 14:08 ` Paul E. McKenney
2019-01-10 14:52 ` Paul E. McKenney
2019-01-09 0:02 ` Andrea Parri
2019-01-09 0:36 ` Anatol Pomozov
2019-01-09 5:35 ` Dmitry Vyukov
2019-01-09 11:24 ` Andrea Parri
2019-01-09 11:55 ` Dmitry Vyukov
2019-01-09 12:11 ` Andrea Parri
2019-01-09 12:29 ` Dmitry Vyukov
2019-01-09 17:10 ` Paul E. McKenney
2019-01-10 8:49 ` Dmitry Vyukov
2019-01-10 12:30 ` Andrea Parri [this message]
2019-01-10 12:38 ` Dmitry Vyukov
2019-01-10 12:46 ` Andrea Parri
2019-01-10 13:25 ` Dmitry Vyukov
2019-01-10 14:50 ` Paul E. McKenney
2019-01-10 12:44 ` Peter Zijlstra
2019-01-10 12:54 ` Dmitry Vyukov
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