* Arjan van de Ven <[email protected]> wrote:
> That case is the simple (and most common) case. Since it uses down()
> only, it can't be irq context. (trylock could be a sign of irq context
> use), and all up()'s are 1) not in irq context either because they're
> in the same function as the down() which isn;t and 2) perfectly
> matched to the down(), eg each down gets one up ---> perfect
> semaphore.
one of the most frequent exceptions to the 'up in a separate function'
rule are seqfile implementations, which all have start(), mid(), stop()
methods, where start() does the down(), stop() does the up(). These can
still be converted to mutexes (and i converted a couple of them), after
manual review.
> The other case on the other side of the spectrum is a down in one
> function and an up in an irq function. Which is a pretty good sign of
> a completion.... (same is true for a specific scenario where kernel
> thread creation is involved and the up() is done in the just created
> thread).
another good sign of completion type of semaphores is the use of
DECLARE_MUTEX_LOCKED(), init_MUTEX_LOCKED(), or sema_init(&sem, 0). In
95% of these cases these signal semaphores used as completions. That is
one reason why i did not add DEFINE_MUTEX_LOCKED(), nor
mutex_init_locked() to the mutex APIs.
the 'struct work' conversion is rare, i've only seen it in XFS so far.
Ingo
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