Re: [PATCH v2 1/3] locking: Document the semantics of spin_is_locked()

[Randy Dunlap]

On 04/03/2018 02:43 PM, David Howells wrote:
> Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote:
> 
>> + * Returns: 1 if @lock is locked, 0 otherwise.
>> + * However, on !CONFIG_SMP builds with !CONFIG_DEBUG_SPINLOCK,
>> + * the return value is always 0 (see include/linux/spinlock_up.h).
>> + * Therefore you should not rely heavily on the return value.
> 
> Seems reasonable.
> 
> It might also want to include a note that the lock isn't necessarily held by
> your own CPU.  I would also use "=n" rather than "!", so maybe something like:
> 
>  * Returns: 1 if @lock is locked, 0 otherwise.
>  *
>  * Note that the function only tells you that the CPU is seen to be locked,

the CPU is locked??

>  * not that it is locked on your CPU.
>  *
>  * Further, on CONFIG_SMP=n builds with CONFIG_DEBUG_SPINLOCK=n, the return
>  * value is always 0 (see include/linux/spinlock_up.h).  Therefore you should
>  * not rely heavily on the return value.
> 
> David
> 


-- 
~Randy