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Date: Tue, 22 Apr 2003 11:25:36 +0200
From: Jens Axboe <axboe@suse.de>
To: Heiko.Rabe@InVision.de
Cc: linux-kernel@vger.kernel.org
Subject: Re: inconsistent usage of
Message-ID: <20030422092536.GH4911@suse.de>
References: <OF07767E6D.29E660DD-ONC1256D10.002B8A2D@invision.de>
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On Tue, Apr 22 2003, Heiko.Rabe@InVision.de wrote:
> I found inconsistent behavoir between SMP oand none SMP kernels using spin
> locks inside driver programming
> As first an simple example:
> 
> static spinlock_t        qtlock               = SPIN_LOCK_UNLOCKED;
> 
> void foo()
> {
>      unsigned long  local_flags;
>      spin_lock_irqsave (&qtlock, local_flags);
>      spin_lock_irqsave (&qtlock, local_flags);
> }

[snip rant]

Check the spinlock implementation. All the above does in UP is
disable/save interrupts twice. The actual spinlock is a nop. As only one
processor can be executing inside the kernel in UP, you only need to
guard against interrupts.

-- 
Jens Axboe