Date: Wed, 11 Nov 2015 19:44:27 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: David Miller <davem@davemloft.net>, will.deacon@arm.com,
        daniel@iogearbox.net, arnd@arndb.de, yang.shi@linaro.org,
        linaro-kernel@lists.linaro.org, eric.dumazet@gmail.com,
        zlim.lnx@gmail.com, ast@kernel.org, linux-kernel@vger.kernel.org,
        netdev@vger.kernel.org, xi.wang@gmail.com, catalin.marinas@arm.com,
        linux-arm-kernel@lists.infradead.org, yhs@plumgrid.com,
        bblanco@plumgrid.com
Subject: Re: [PATCH 2/2] arm64: bpf: add BPF XADD instruction
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On Wed, Nov 11, 2015 at 07:31:28PM +0100, Peter Zijlstra wrote:
> > Add new one that does 'fetch_and_add' ? What is the real use case it
> > will be used for?
> 
> Look at all the atomic_{add,dec}_return*() users in the kernel. A typical
> example would be a reader-writer lock implementations. See
> include/asm-generic/rwsem.h for examples.

Maybe a better example would be refcounting, where you free on 0.

	if (!fetch_add(&obj->ref, -1))
		free(obj);


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