linux-kernel - Re: Locking in the clk API

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 for Android: free password hash cracker in your pocket

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

Date:	Tue, 11 Jan 2011 12:11:29 +0800
From:	Jeremy Kerr <jeremy.kerr@...onical.com>
To:	Paul Mundt <lethal@...ux-sh.org>
Cc:	linux-sh@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Ben Herrenschmidt <benh@...nel.crashing.org>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	"Uwe Kleine-K??nig" <u.kleine-koenig@...gutronix.de>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>
Subject: Re: Locking in the clk API

Hi Paul,

> This looks like a complete disaster, and is also completely inconsistent
> with how the API is being used by the vast majority of users today.

I've been basing this on the mxc clock code, which acquires a mutex for all 
clk_enable()s. This may not be representative of the majority of clock usage.

>From a quick search there are a few other cases of non-atomic clock usage:

tcc:		clk_enable() acquires a global clocks_mutex
tegra:	has a clk_enable_cansleep()
davinci: clk_set_parent() aquires a global clocks_mutex

Excluding the davinci code (we won't worry about set_parent for now...), if we 
can port mxc and tcc to a sleepable clk_enable, perhaps we could just go with 
purely atomic operations.

We'd still need some method of using sleeping clocks though. How about making 
clk_enable() BUG if the clock is not atomic, and add clk_enable_cansleep() for 
the cases where clk->ops.enable may sleep.

Do we need something similar for other parts of the API? (clk_set_rate?)

Cheers,

Jeremy
--
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/