Date: Sat, 14 Jan 2006 14:38:40 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Arjan van de Ven <arjan@infradead.org>
Cc: Ingo Oeser <ioe-lkml@rameria.de>, linux-kernel@vger.kernel.org,
       Andrew Morton <akpm@osdl.org>, Linus Torvalds <torvalds@osdl.org>,
       Jes Sorensen <jes@trained-monkey.org>, Greg KH <greg@kroah.com>
Subject: Re: [patch 00/62] sem2mutex: -V1
Message-ID: <20060114133840.GA4038@elte.hu>
References: <20060113124402.GA7351@elte.hu> <200601131925.34971.ioe-lkml@rameria.de> <20060113195658.GA3780@elte.hu> <200601141416.20055.ioe-lkml@rameria.de> <1137245466.3014.20.camel@laptopd505.fenrus.org>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <1137245466.3014.20.camel@laptopd505.fenrus.org>
User-Agent: Mutt/1.4.2.1i
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1648
Lines: 36


* Arjan van de Ven <arjan@infradead.org> wrote:

> That case is the simple (and most common) case. Since it uses down() 
> only, it can't be irq context. (trylock could be a sign of irq context 
> use), and all up()'s are 1) not in irq context either because they're 
> in the same function as the down() which isn;t and 2) perfectly 
> matched to the down(), eg each down gets one up ---> perfect 
> semaphore.

one of the most frequent exceptions to the 'up in a separate function' 
rule are seqfile implementations, which all have start(), mid(), stop() 
methods, where start() does the down(), stop() does the up(). These can 
still be converted to mutexes (and i converted a couple of them), after 
manual review.

> The other case on the other side of the spectrum is a down in one 
> function and an up in an irq function. Which is a pretty good sign of 
> a completion.... (same is true for a specific scenario where kernel 
> thread creation is involved and the up() is done in the just created 
> thread).

another good sign of completion type of semaphores is the use of 
DECLARE_MUTEX_LOCKED(), init_MUTEX_LOCKED(), or sema_init(&sem, 0). In 
95% of these cases these signal semaphores used as completions. That is 
one reason why i did not add DEFINE_MUTEX_LOCKED(), nor 
mutex_init_locked() to the mutex APIs.

the 'struct work' conversion is rare, i've only seen it in XFS so far.

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