From: Peter Zijlstra <peterz@infradead.org>
To: Andy Lutomirski <luto@kernel.org>
Cc: X86 ML <x86@kernel.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
LKML <linux-kernel@vger.kernel.org>,
Nicholas Piggin <npiggin@gmail.com>,
Arnd Bergmann <arnd@arndb.de>, Anton Blanchard <anton@ozlabs.org>
Subject: Re: [PATCH 3/3] membarrier: Propagate SYNC_CORE and RSEQ actions more carefully
Date: Tue, 1 Dec 2020 19:55:56 +0100 [thread overview]
Message-ID: <20201201185556.GV3040@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CALCETrUZHWvjO8otEWat6SDwDFRdV0iSp=RZDaHnyytJ=4a6cg@mail.gmail.com>
On Tue, Dec 01, 2020 at 10:09:22AM -0800, Andy Lutomirski wrote:
> > smp_call_function_single(.wait=1) already orders against completion of
> > the IPI. Do we really need more?
>
> What kind of order does it provide? A quick skim of the code suggests
> that it's an acquire barrier, but I think we need a full sequential
> consistency barrier, at least on sufficiently weakly ordered
> architectures. On x86, loads are ordered and this is probably
> irrelevant. Also, this barrier was already there (it's the one I
> deleted below), and I think that removing it should be its own patch
> if we want to go that route.
smp_mb()
raise-IPI ---->
<IPI>
/* do crud */
STORE-RELEASE csd->lock, 0;
</IPI/
LOAD-ACQUIRE csd->lock
prev parent reply other threads:[~2020-12-01 18:56 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-30 17:50 [PATCH 0/3] membarrier fixes Andy Lutomirski
2020-11-30 17:50 ` [PATCH 1/3] x86/membarrier: Get rid of a dubious optimization Andy Lutomirski
2020-12-01 14:39 ` Mathieu Desnoyers
2020-12-01 17:47 ` Andy Lutomirski
2020-11-30 17:50 ` [PATCH 2/3] membarrier: Add an actual barrier before rseq_preempt() Andy Lutomirski
2020-12-01 10:06 ` Peter Zijlstra
2020-12-01 14:31 ` Mathieu Desnoyers
2020-12-01 17:55 ` Andy Lutomirski
2020-11-30 17:50 ` [PATCH 3/3] membarrier: Propagate SYNC_CORE and RSEQ actions more carefully Andy Lutomirski
2020-12-01 10:16 ` Peter Zijlstra
2020-12-01 14:28 ` Mathieu Desnoyers
2020-12-01 18:12 ` Andy Lutomirski
2020-12-01 18:29 ` Mathieu Desnoyers
2020-12-01 18:48 ` Andy Lutomirski
2020-12-01 20:51 ` Mathieu Desnoyers
2020-12-01 18:09 ` Andy Lutomirski
2020-12-01 18:53 ` Peter Zijlstra
2020-12-01 18:55 ` Peter Zijlstra [this message]
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