linux-kernel - Re: [PATCH 2.6.36 1/1 RESEND] kernel SPIN_LOCK_UNLOCKED changed to __SPIN_LOCK

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Date:	Mon, 15 Nov 2010 09:24:04 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Atul Sowani <sowani@...il.com>
Cc:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	alan@...ux.intel.com, ralf@...ux-mips.org
Subject: Re: [PATCH 2.6.36 1/1 RESEND] kernel SPIN_LOCK_UNLOCKED changed to
	__SPIN_LOCK_UNLOCKED()

On Sun, Nov 14, 2010 at 12:01:06AM +0530, Atul Sowani wrote:
> There are still some files containing .lock = SPIN_LOCK_UNLOCKED type
> assignments which should be converted to __SPIN_LOCK_UNLOCKED().
> Corrected spacing between __SPIN_LOCK_UNLOCKED and ( for ARM.

Thinking about the ARM bit, I'll have to NAK this patch.

> diff -uprN a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
> --- a/arch/arm/kernel/smp.c	2010-10-21 02:00:22.000000000 +0530
> +++ b/arch/arm/kernel/smp.c	2010-11-07 00:47:32.000000000 +0530
> @@ -56,7 +56,7 @@ struct ipi_data {
>  };
> 
>  static DEFINE_PER_CPU(struct ipi_data, ipi_data) = {
> -	.lock	= SPIN_LOCK_UNLOCKED,
> +	.lock	= __SPIN_LOCK_UNLOCKED(ipi_data.lock),
>  };

This lock is in the percpu data area.  This means that when other CPUs
are brought online, and therefore other percpu areas are instantiated,
this lock will be mis-initialized (the pointers et.al. will be pointing
at the original percpu instance.)

So NAK, this will break.

We can either go back to a static array for this, initialize the lock
manually (though this could be problematical), or we require to go to
per-ipi type interrupts for all SMP architectures.
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