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

[David Howells]

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,
 * 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