linux-kernel - RE: [RFC][PATCH 2/7] kref: Add kref

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Date:   Mon, 21 Nov 2016 15:39:19 +0000
From:   "Reshetova, Elena" <elena.reshetova@...el.com>
To:     David Windsor <dwindsor@...il.com>
CC:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        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()

> By the way, there are several sites where the use of
> atomic_t/atomic_wrap_t as a counter ventures beyond the standard (inc,
> dec, add, sub, read, set) operations we're planning on implementing
> for both refcount_t and stats_t. 

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. 

Also, simple atomic_dec() is used pretty much everywhere for counters, which we don’t have a straight match in refcount_t API.