linux-kernel - Re: [KJ] remove SPIN_LOCK

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Message-ID: <Pine.LNX.4.64.0704110140480.7851@CPE00045a9c397f-CM001225dbafb6>
Date:	Wed, 11 Apr 2007 01:47:09 -0400 (EDT)
From:	"Robert P. J. Day" <rpjday@...dspring.com>
To:	Matthew Wilcox <matthew@....cx>
cc:	Roland Dreier <rdreier@...co.com>, kernelnewbies@...linux.org,
	kernel-janitors@...ts.osdl.org,
	Jan Engelhardt <jengelh@...ux01.gwdg.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [KJ] remove SPIN_LOCK_UNLOCKED

On Tue, 10 Apr 2007, Matthew Wilcox wrote:

> On Tue, Apr 10, 2007 at 05:45:07PM -0400, Robert P. J. Day wrote:
> > that works fine if you're defining a single spinlock, but what do you
> > do in cases like this:
> >
> > arch/sparc/lib/atomic32.c:      [0 ... (ATOMIC_HASH_SIZE-1)] = SPIN_LOCK_UNLOCKED
> >
> > that is, when you're assigning an array of them?  you still need
> > some kind of generic, unnamed spinlock in those circumstances, no?
>
> That's a special case for architecture-only code.  It's not to be
> used by drivers.

be that as it may, it still means you need to take it into account
whenever someone says they want to entirely remove the
SPIN_LOCK_UNLOCKED macro from the source tree, as suggested in
Documentation/spinlocks.txt.

if you do that removal, you can always replace SPIN_LOCK_UNLOCKED with
its current definition of __SPIN_LOCK_UNLOCKED(old_style_spin_init),
or what have you.  but you would obviously have to replace it with
*something* that represents an unnamed spinlock if SPIN_LOCK_UNLOCKED
goes away.

rday

p.s.  just FYI:

$ grep -r "\.\.\..*SPIN_LOCK_UNLOCKED" *
arch/sparc/lib/atomic32.c:      [0 ... (ATOMIC_HASH_SIZE-1)] = SPIN_LOCK_UNLOCKED
arch/cris/arch-v32/kernel/smp.c:spinlock_t cris_atomic_locks[] = { [0 ... LOCK_COUNT - 1] = SPIN_LOCK_UNLOCKED};
arch/parisc/lib/bitops.c:       [0 ... (ATOMIC_HASH_SIZE-1)]  = __RAW_SPIN_LOCK_UNLOCKED
arch/mips/kernel/gdb-stub.c:    [0 ... NR_CPUS-1] = __RAW_SPIN_LOCK_UNLOCKED,
arch/powerpc/platforms/iseries/htab.c:  { [0 ... 63] = SPIN_LOCK_UNLOCKED};

so, as matthew says, it's clearly not for drivers.

-- 
========================================================================
Robert P. J. Day
Linux Consulting, Training and Annoying Kernel Pedantry
Waterloo, Ontario, CANADA

http://fsdev.net/wiki/index.php?title=Main_Page
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