From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: Joe Perches <joe@perches.com>
Cc: Randy Dunlap <randy.dunlap@oracle.com>,
linux-kernel@vger.kernel.org, cpufreq@vger.kernel.org,
Dave Jones <davej@redhat.com>,
Greg Kroah-Hartman <gregkh@suse.de>,
"H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
x86@vger.kernel.org, Len Brown <len.brown@intel.com>,
Mike Travis <travis@sgi.com>,
Rusty Russell <rusty@rustcorp.com.au>,
Thomas Gleixner <tglx@linutronix.de>,
Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Subject: Re: [PATCH 1/3] kernel.h: Add DO_ONCE statement expression macro
Date: Fri, 22 May 2009 00:41:27 +0100 [thread overview]
Message-ID: <20090522004127.1a91056b@lxorguk.ukuu.org.uk> (raw)
In-Reply-To: <1242948762.3373.143.camel@Joe-Laptop.home>
> Add a DO_ONCE statement expression analogous to printk_once
> that executes any arbitrary statement exactly once.
Your implementation is racy. Its also hiding stuff in macro magic which
is asking for accidents to happen.
The natural kernel way to write this is
if (!test_and_set_bit(....))
which is a lot more obvious than a magic macro, doesn't race and can use
other bits in an existing set of flags and be used as a
"do-once-for-this-object-instance" - which is almost always want you want.
Alan
next prev parent reply other threads:[~2009-05-21 23:41 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-05-21 23:00 [PATCH 0/3] Introduce and use " Joe Perches
2009-05-21 23:00 ` [PATCH 1/3] kernel.h: Add " Joe Perches
2009-05-21 23:27 ` Randy Dunlap
2009-05-21 23:32 ` Joe Perches
2009-05-21 23:36 ` H. Peter Anvin
2009-05-21 23:41 ` Alan Cox [this message]
2009-05-22 0:27 ` Al Viro
2009-05-22 1:09 ` Joe Perches
2009-05-25 6:45 ` Rusty Russell
2009-05-26 2:42 ` Andrew Morton
2009-05-21 23:00 ` [PATCH 2/3] arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c: Use DO_ONCE & spelling fix Joe Perches
2009-05-21 23:26 ` Dave Jones
2009-05-21 23:34 ` Joe Perches
2009-05-21 23:47 ` Dave Jones
2009-05-21 23:52 ` Joe Perches
2009-05-21 23:00 ` [PATCH 3/3] kernel.h: Remove unused printk_once Joe Perches
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