Date: Wed, 29 May 2019 22:02:43 +0100 From: David Howells <dhowells@...hat.com> To: Jann Horn <jannh@...gle.com> Cc: dhowells@...hat.com, Greg KH <gregkh@...uxfoundation.org>, Al Viro <viro@...iv.linux.org.uk>, raven@...maw.net, linux-fsdevel <linux-fsdevel@...r.kernel.org>, Linux API <linux-api@...r.kernel.org>, linux-block@...r.kernel.org, keyrings@...r.kernel.org, linux-security-module <linux-security-module@...r.kernel.org>, kernel list <linux-kernel@...r.kernel.org>, Kees Cook <keescook@...omium.org>, Kernel Hardening <kernel-hardening@...ts.openwall.com> Subject: Re: [PATCH 1/7] General notification queue with user mmap()'able ring buffer Jann Horn <jannh@...gle.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
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