linux-kernel - Re: [PATCH 3/4] IPMI: convert locked counters to atomics

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Message-Id: <20080214111143.7e0937ea.akpm@linux-foundation.org>
Date:	Thu, 14 Feb 2008 11:11:43 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	minyard@....org
Cc:	Linux Kernel <linux-kernel@...r.kernel.org>,
	OpenIPMI Developers <openipmi-developer@...ts.sourceforge.net>,
	Konstantin Baydarov <kbaidarov@...mvista.com>
Subject: Re: [PATCH 3/4] IPMI: convert locked counters to atomics

> +	for (i = 0; i < IPMI_NUM_STATS; i++)
> +		atomic_set(&intf->stats[i], 0);

And this is why it would be very hard for any architecture to ever
implement atomic_t as

struct atomic_t {
	int counter;
	spinlock_t lock;
};

The interface assumes that atomic_set() fully initialises the atomic_t, and
that atomic_set() can be used agaisnt both an uninitialised atomic_t and
against an already-initialised atomic_t.  IOW, we don't have atomic_init().

So would our hypothetical future architcture's atomic_set() do spin_lock(),
or would it do spin_lock_init()?  Either one is wrong in many atomic_set
callsites.

Oh well.
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