Messages in this thread |  | | Date | Tue, 3 Apr 2018 16:04:43 -0400 (EDT) | From | Alan Stern <> | Subject | Re: [PATCH v2 1/3] locking: Document the semantics of spin_is_locked() |
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On Tue, 3 Apr 2018, Andrea Parri wrote:
> On Tue, Apr 03, 2018 at 04:23:07PM +0100, David Howells wrote: > > Andrea Parri <andrea.parri@amarulasolutions.com> wrote: > > > > > Sorry, but I don't understand your objection: are you suggesting to add > > > something like "Always return 0 on !SMP" to the comment? what else? > > > > Something like that, possibly along with a warning that this might not be what > > you want. You might actually want it to return true on !SMP, it depends on > > what you're using it for. > > I ended up with the following revision. I hesitated on whether to refer > to 'include/linux/spinlock_up.h' or not, but in the end I decided to not > include the reference. Please let me know what you think about this.
> +/** > + * spin_is_locked() - Check whether a spinlock is locked. > + * @lock: Pointer to the spinlock. > + * > + * This function is NOT required to provide any memory ordering > + * guarantees; it could be used for debugging purposes or, when > + * additional synchronization is needed, accompanied with other > + * constructs (memory barriers) enforcing the synchronization. > + * > + * Return: 1, if @lock is (found to be) locked; 0, otherwise. > + * > + * Remark that this primitve can return a fixed value > + * under certain !SMP configurations.
I would change these last two paragraphs as follows:
+ * 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.
Alan
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