linux-kernel - Re: [PATCH 1/3] kernel.h: Add DO_ONCE statement expression macro

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20090522004127.1a91056b@lxorguk.ukuu.org.uk>
Date:	Fri, 22 May 2009 00:41:27 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Joe Perches <joe@...ches.com>
Cc:	Randy Dunlap <randy.dunlap@...cle.com>,
	linux-kernel@...r.kernel.org, cpufreq@...r.kernel.org,
	Dave Jones <davej@...hat.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
	x86@...r.kernel.org, Len Brown <len.brown@...el.com>,
	Mike Travis <travis@....com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Thomas Gleixner <tglx@...utronix.de>,
	Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>
Subject: Re: [PATCH 1/3] kernel.h: Add DO_ONCE statement expression macro

> 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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/