Messages in this thread | | | Date | Fri, 7 Apr 2023 21:36:30 +0100 | From | Matthew Wilcox <> | Subject | Re: [PATCH v2 1/2] Change DEFINE_SEMAPHORE() to take a number argument |
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On Wed, Apr 05, 2023 at 01:35:04PM -0700, Luis Chamberlain wrote: > diff --git a/include/linux/semaphore.h b/include/linux/semaphore.h > index 6694d0019a68..2d6aa3fd7861 100644 > --- a/include/linux/semaphore.h > +++ b/include/linux/semaphore.h > @@ -25,8 +25,15 @@ struct semaphore { > .wait_list = LIST_HEAD_INIT((name).wait_list), \ > } > > -#define DEFINE_SEMAPHORE(name) \ > - struct semaphore name = __SEMAPHORE_INITIALIZER(name, 1) > +/* > + * There is a big difference between a binary semaphore and a mutex. > + * You cannot call mutex_unlock() from IRQ context because it takes an > + * internal mutex spin_lock in a non-IRQ-safe manner. Both try_lock() > + * and unlock() can be called from IRQ context. A mutex must also be > + * released in the same context that locked it. > + */
I think this confuses cause and effect. How about this:
/* * Binary semaphores and mutexes differ in that mutexes have an owner * so they cannot be used from interrupt context and cannot be passed * from one thread to another. down_trylock() and up() can be called * from interrupt context. */
Or this:
/* * Unlike mutexes, binary semaphores do not have an owner, so up() can * be called in a different thread from the one which called down(). * It is also safe to call down_trylock() and up() from interrupt * context. */
I'd like to mention completions as an alternative to semaphores, but can't figure out a nice way to fit that in.
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