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From: Peter Zijlstra <peterz@infradead.org>
To: Daniel Borkmann <daniel@iogearbox.net>
Cc: alexei.starovoitov@gmail.com, paulmck@linux.vnet.ibm.com,
	will.deacon@arm.com, acme@redhat.com, yhs@fb.com,
	john.fastabend@gmail.com, netdev@vger.kernel.org
Subject: Re: [PATCH bpf-next 3/3] bpf, libbpf: use proper barriers in perf ring buffer walk
Date: Wed, 17 Oct 2018 17:51:35 +0200	[thread overview]
Message-ID: <20181017155135.GN3121@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20181017144156.16639-4-daniel@iogearbox.net>

On Wed, Oct 17, 2018 at 04:41:56PM +0200, Daniel Borkmann wrote:
> +static __u64 bpf_perf_read_head(struct perf_event_mmap_page *header)
> +{
> +	__u64 data_head = READ_ONCE(header->data_head);
> +
> +	smp_rmb();
> +	return data_head;
> +}
> +
> +static void bpf_perf_write_tail(struct perf_event_mmap_page *header,
> +				__u64 data_tail)
> +{
> +	smp_mb();
> +	header->data_tail = data_tail;
> +}

Same coments, either smp_load_acquire()/smp_store_release() or at the
very least a WRITE_ONCE() there.

  reply	other threads:[~2018-10-17 23:48 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-17 14:41 [PATCH bpf-next 0/3] improve and fix barriers for walking perf rb Daniel Borkmann
2018-10-17 14:41 ` [PATCH bpf-next 1/3] tools: add smp_* barrier variants to include infrastructure Daniel Borkmann
2018-10-17 14:41 ` [PATCH bpf-next 2/3] tools, perf: use smp_{rmb,mb} barriers instead of {rmb,mb} Daniel Borkmann
2018-10-17 15:50   ` Peter Zijlstra
2018-10-17 23:10     ` Daniel Borkmann
2018-10-18  8:14       ` Peter Zijlstra
2018-10-18 15:04         ` Daniel Borkmann
2018-10-18 15:33           ` Alexei Starovoitov
2018-10-18 19:00             ` Daniel Borkmann
2018-10-19  3:53               ` Alexei Starovoitov
2018-10-19 11:02                 ` Will Deacon
2018-10-19 11:56                   ` Paul E. McKenney
2018-10-19  8:04             ` Peter Zijlstra
2018-10-19  9:44           ` Peter Zijlstra
2018-10-19 10:37             ` Daniel Borkmann
2018-10-17 14:41 ` [PATCH bpf-next 3/3] bpf, libbpf: use proper barriers in perf ring buffer walk Daniel Borkmann
2018-10-17 15:51   ` Peter Zijlstra [this message]
2018-10-17 15:03 ` [PATCH bpf-next 0/3] improve and fix barriers for walking perf rb Arnaldo Carvalho de Melo

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