Re: inconsistent usage of

[Jens Axboe <axboe@suse.de>]

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