Re: [Xen-devel] [PATCH] spinlock: improve spin_is_locked() for recursive locks

[David Vrabel <david.vrabel@xxxxxxxxxx>]

On 24/03/16 11:30, Jan Beulich wrote:
> Recursive locks know their current owner, and since we use the function
> solely to determine whether a particular lock is being held by the
> current CPU (which so far has been an imprecise check), make actually
> check the owner for recusrively acquired locks.

What's the expected behaviour of _spin_is_locked() if the lock is held
by another CPU?

Before it may return true if it is held by another CPU, now it will
always return false in this case.

David

> --- a/xen/common/spinlock.c
> +++ b/xen/common/spinlock.c
> @@ -188,7 +188,9 @@ void _spin_unlock_irqrestore(spinlock_t
>  int _spin_is_locked(spinlock_t *lock)
>  {
>      check_lock(&lock->debug);
> -    return lock->tickets.head != lock->tickets.tail;
> +    return lock->recurse_cpu == SPINLOCK_NO_CPU
> +           ? lock->tickets.head != lock->tickets.tail
> +           : lock->recurse_cpu == smp_processor_id();
>  }
>  
>  int _spin_trylock(spinlock_t *lock)
> 
> 
> 
> 
> 
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> 


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