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From:   David Howells <dhowells@redhat.com>
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To:     Jann Horn <jannh@google.com>
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        Al Viro <viro@zeniv.linux.org.uk>, raven@themaw.net,
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Subject: Re: [PATCH 1/7] General notification queue with user mmap()'able ring buffer
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Date:   Wed, 29 May 2019 22:02:43 +0100
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Jann Horn <jannh@google.com> 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.

David