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SubjectRe: [PATCH v2 1/3] locking: Document the semantics of spin_is_locked()
Date
Alan Stern <stern@rowland.harvard.edu> 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

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