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Date: Wed, 29 May 2019 22:02:43 +0100
From: David Howells <>
To: Jann Horn <>
Cc:, Greg KH <>,
    Al Viro <>,,
    linux-fsdevel <>,
    Linux API <>,,,
    linux-security-module <>,
    kernel list <>,
    Kees Cook <>,
    Kernel Hardening <>
Subject: Re: [PATCH 1/7] General notification queue with user mmap()'able ring buffer

Jann Horn <> wrote:

> Does this mean that refcount_read() isn't sufficient for what you want
> to do with tracing (because for some reason you actually need to know
> the values atomically at the time of increment/decrement)?

Correct.  There's a gap and if an interrupt or something occurs, it's
sufficiently big for the refcount trace to go weird.

I've seen it in afs/rxrpc where the incoming network packets that are part of
the rxrpc call flow disrupt the refcounts noted in trace lines.


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