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Message-ID: <2236FBA76BA1254E88B949DDB74E612B41C156AE@IRSMSX102.ger.corp.intel.com>
Date: Mon, 21 Nov 2016 19:27:29 +0000
From: "Reshetova, Elena" <elena.reshetova@...el.com>
To: Peter Zijlstra <peterz@...radead.org>
CC: David Windsor <dwindsor@...il.com>,
Alexei Starovoitov <alexei.starovoitov@...il.com>,
Kees Cook <keescook@...omium.org>,
Greg KH <gregkh@...uxfoundation.org>,
Will Deacon <will.deacon@....com>,
"Arnd Bergmann" <arnd@...db.de>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...nel.org>,
"H. Peter Anvin" <hpa@...or.com>,
LKML <linux-kernel@...r.kernel.org>,
Daniel Borkmann <daniel@...earbox.net>
Subject: RE: [RFC][PATCH 2/7] kref: Add kref_read()
> On Mon, Nov 21, 2016 at 04:49:15PM +0100, Peter Zijlstra wrote:
> > > Speaking of non-fitting patterns. This one is quite common in
> > > networking code for refcounters:
> > >
> > > if (atomic_cmpxchg(&cur->refcnt, 1, 0) == 1) {} This is from
> > > net/netfilter/nfnetlink_acct.c, but there are similar ones in other
> > > places.
> >
> > Cute, but weird it doesn't actually decrement if not 1.
>
> Hurgh.. creative refcounting that. The question is how much of that do
> we want to support? It really must not decrement there.
And one more creative usage:
http://lxr.free-electrons.com/source/net/ipv4/udp.c#L1940
if (!sk || !atomic_inc_not_zero_hint(&sk->sk_refcnt, 2))
return;
I didn't even guess anyone is using atomic_inc_not_zero_hint...
But network code keeps surprising me today :)
So, yes, I guess the question is what to do with these cases really?
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