linux-kernel - Re: [PATCH v6 02/13] user_events: Add minimal support for trace

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Message-ID: <20211209151930.709d3d0b@gandalf.local.home>
Date:   Thu, 9 Dec 2021 15:19:30 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Beau Belgrave <beaub@...ux.microsoft.com>
Cc:     mhiramat@...nel.org, linux-trace-devel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 02/13] user_events: Add minimal support for
 trace_event into ftrace

On Thu, 9 Dec 2021 12:11:12 -0800
Beau Belgrave <beaub@...ux.microsoft.com> wrote:

> I guess I am being paranoid about an architecture that does not have
> automatic cache consistency and while the write / read don't happen at
> the exact time, they happen close together. Close enough that one CPU
> reads the old value from a cache line and gets it wrong.
> 
> I don't believe that is possible on Intel, but I don't know if it's
> possible on other architectures (especially older ones).

If this was possible, then there would be a lot more bugs out there than
this one. For one thing, the file descriptor itself would be freed while
accessed.

-- Steve