linux-kernel - Re: [PATCH 1/2] serial: samsung: Move uart_register

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]

Date:	Tue, 21 Jan 2014 09:45:29 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
Cc:	Greg KH <gregkh@...uxfoundation.org>,
	Tushar Behera <tushar.behera@...aro.org>,
	linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
	linux-samsung-soc@...r.kernel.org, jslaby@...e.cz,
	ben.dooks@...ethink.co.uk, broonie@...nel.org
Subject: Re: [PATCH 1/2] serial: samsung: Move uart_register_driver call to
	device probe

On Tue, Jan 21, 2014 at 09:25:31AM +0000, One Thousand Gnomes wrote:
> > static DEFINE_MUTEX(foo_mutex);
> > static unsigned foo_devices;
> > 
> > static int foo_probe(struct platform_device *pdev)
> > {
> > 	int ret;
> > 
> > 	mutex_lock(&foo_mutex);
> > 	if (foo_devices++ == 0)
> > 		uart_register_driver(&driver);
> > 
> > 	ret = foo_really_probe_device(pdev);
> 
> We have atomic_inc_and_test and atomic_dec_and_test so it's
> fractionally less ugly.

How do atomics help here?  If we do this as:

	if (atomic_inc_and_test(&foo_atomic))
		uart_register_driver(&driver);

Then let's think about what can happen:

	CPU0				CPU1
	foo_probe
	atomic_inc_and_test() == true
		uart_register_driver
					foo_probe
					atomic_inc_and_test()
					really_probe_foo()
						*bang*

-- 
FTTC broadband for 0.8mile line: 5.8Mbps down 500kbps up.  Estimation
in database were 13.1 to 19Mbit for a good line, about 7.5+ for a bad.
Estimate before purchase was "up to 13.2Mbit".
--
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/