linux-kernel - Re: [PATCH 2/7] kfifo: move out spinlock

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Message-Id: <20090816163422.a147a918.akpm@linux-foundation.org>
Date:	Sun, 16 Aug 2009 16:34:22 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Stefani Seibold <stefani@...bold.net>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Arnd Bergmann <arnd@...db.de>,
	Andi Kleen <andi@...stfloor.org>,
	Amerigo Wang <xiyou.wangcong@...il.com>,
	Joe Perches <joe@...ches.com>
Subject: Re: [PATCH 2/7] kfifo: move out spinlock

On Sun, 16 Aug 2009 23:58:43 +0100 Alan Cox <alan@...rguk.ukuu.org.uk> wrote:

> On Sun, 16 Aug 2009 22:46:30 +0200
> Stefani Seibold <stefani@...bold.net> wrote:
> 
> > Move the pointer to the spinlock out of struct kfifo. Most
> > users in tree do not actually use a spinlock, so the few
> > exceptions now have to call kfifo_{get,put}_locked, which takes
> > an extra argument to a spinlock.
> 
> NAK this one for the moment
> 
> We are about to set fifo loose through all the USB and some other
> char/serial drivers all of which will use the spinlock facility.

That sounds like a good reason for applying this patch first.

kfifo has no business assuming that the caller wants to use
spin_lock() locking.

If we want to add wrapper helpers around kfifo to reduce code
duplication in callers, and if one of those wrapper helpers provides
spinlock-based locking then fine.

But the happens-to-use-spin_lock functions shouldn't be called
kfifo_get(), because that steals namespace from the unlocked functions,
and makes the naming for the happens-to-use-mutex_lock functions look
weird.

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