From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
To: Andy Lutomirski <luto@kernel.org>
Cc: x86 <x86@kernel.org>, linux-kernel <linux-kernel@vger.kernel.org>,
Nicholas Piggin <npiggin@gmail.com>,
Arnd Bergmann <arnd@arndb.de>, Anton Blanchard <anton@ozlabs.org>,
stable <stable@vger.kernel.org>
Subject: Re: [PATCH v2 2/4] membarrier: Add an actual barrier before rseq_preempt()
Date: Wed, 2 Dec 2020 14:40:43 -0500 (EST) [thread overview]
Message-ID: <203775582.21.1606938043613.JavaMail.zimbra@efficios.com> (raw)
In-Reply-To: <510cb07946be056d2da7dda721bbf444c288751b.1606923183.git.luto@kernel.org>
----- On Dec 2, 2020, at 10:35 AM, Andy Lutomirski luto@kernel.org wrote:
> It seems to me that most RSEQ membarrier users will expect any
> stores done before the membarrier() syscall to be visible to the
> target task(s). While this is extremely likely to be true in
> practice, nothing actually guarantees it by a strict reading of the
> x86 manuals. Rather than providing this guarantee by accident and
> potentially causing a problem down the road, just add an explicit
> barrier.
>
> Cc: stable@vger.kernel.org
> Signed-off-by: Andy Lutomirski <luto@kernel.org>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> ---
> kernel/sched/membarrier.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c
> index 5a40b3828ff2..6251d3d12abe 100644
> --- a/kernel/sched/membarrier.c
> +++ b/kernel/sched/membarrier.c
> @@ -168,6 +168,14 @@ static void ipi_mb(void *info)
>
> static void ipi_rseq(void *info)
> {
> + /*
> + * Ensure that all stores done by the calling thread are visible
> + * to the current task before the current task resumes. We could
> + * probably optimize this away on most architectures, but by the
> + * time we've already sent an IPI, the cost of the extra smp_mb()
> + * is negligible.
> + */
> + smp_mb();
> rseq_preempt(current);
> }
>
> --
> 2.28.0
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
next prev parent reply other threads:[~2020-12-02 19:41 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-02 15:35 [PATCH v2 0/4] membarrier fixes Andy Lutomirski
2020-12-02 15:35 ` [PATCH v2 1/4] x86/membarrier: Get rid of a dubious optimization Andy Lutomirski
2020-12-02 15:35 ` [PATCH v2 2/4] membarrier: Add an actual barrier before rseq_preempt() Andy Lutomirski
2020-12-02 19:40 ` Mathieu Desnoyers [this message]
2020-12-02 15:35 ` [PATCH v2 3/4] membarrier: Explicitly sync remote cores when SYNC_CORE is requested Andy Lutomirski
2020-12-02 19:43 ` Mathieu Desnoyers
2020-12-02 15:35 ` [PATCH v2 4/4] membarrier: Execute SYNC_CORE on the calling thread Andy Lutomirski
2020-12-02 19:39 ` Mathieu Desnoyers
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