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Date: Tue, 22 Apr 2003 10:21:38 +0100
From: viro@parcelfarce.linux.theplanet.co.uk
To: Heiko.Rabe@InVision.de
Cc: linux-kernel@vger.kernel.org
Subject: Re: inconsistent usage of
Message-ID: <20030422092138.GS10374@parcelfarce.linux.theplanet.co.uk>
References: <OF07767E6D.29E660DD-ONC1256D10.002B8A2D@invision.de>
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On Tue, Apr 22, 2003 at 10:11:11AM +0200, 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);
> }
> 
> Calling the function foo() works proper in none SMP kernels. I assume, the

... only because spinlocks are no-op on UP.

> spinlocks internaly will be initialized as
> recursive semaphore as default. So it is possible to aquire it more than
> once by the same thread.

Spinlocks are *not* recursive.  The code above is a bug - it's just that
on non-SMP it doesn't get caught.

Spinlock is a mutex, not a recursive sempahore.