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Date: Thu, 11 Jan 2024 09:57:40 +0000
From: Vincent Donnefort <vdonnefort@google.com>
To: Masami Hiramatsu <mhiramat@kernel.org>
Cc: rostedt@goodmis.org, linux-kernel@vger.kernel.org,
	linux-trace-kernel@vger.kernel.org, mathieu.desnoyers@efficios.com,
	kernel-team@android.com
Subject: Re: [PATCH v10 1/2] ring-buffer: Introducing ring-buffer mapping
 functions
Message-ID: <ZZ-7lAdAUxlwoY0z@google.com>
References: <20240105094729.2363579-1-vdonnefort@google.com>
 <20240105094729.2363579-2-vdonnefort@google.com>
 <20240109234230.e99da87104d58fee59ad75c6@kernel.org>
 <ZZ1ir0edlY3OzjyC@google.com>
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[...]

> > > +	 */
> > > +	smp_wmb();
> > > +	WRITE_ONCE(cpu_buffer->mapped, 1);
> > > +
> > > +	/* Init meta_page values unless the writer did it already */
> > > +	cmpxchg(&cpu_buffer->meta_page->entries, 0,
> > > +		local_read(&cpu_buffer->entries));
> > > +	cmpxchg(&cpu_buffer->meta_page->overrun, 0,
> > > +		local_read(&cpu_buffer->overrun));
> > > +	cmpxchg(&cpu_buffer->meta_page->subbufs_touched, 0,
> > > +		local_read(&cpu_buffer->pages_touched));
> > > +	cmpxchg(&cpu_buffer->meta_page->subbufs_lost, 0,
> > > +		local_read(&cpu_buffer->pages_lost));
> > 
> > Instead of using these cmpxchg, can we move this initialization before
> > smp_wmb()? Thus we can avoid conflict with rb_update_meta_page()
> 
> Good point, Not sure why I made this more complicated than it should be.

Ha, I know, that was before v6, where the writer was updating all of that. From
v6 the update has been moved to the irq_rb_work.

> 
> > 
> > Thank you,
> >
> 
> [...]