As discussed in [1], removing __cond_lock() will improve the readability
of trylock code. Now that Sparse context tracking support has been
removed, we can also remove __cond_lock().

Change existing APIs to either drop __cond_lock() completely, or make
use of the __cond_acquires() function attribute instead.

In particular, spinlock and rwlock implementations required switching
over to inline helpers rather than statement-expressions for their
trylock_* variants.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/all/20250207082832.GU7145@noisy.programming.kicks-ass.net/ [1]
Link: https://patch.msgid.link/20251219154418.3592607-25-elver@google.com

Add a cond_lock annotation for lockref_put_or_lock to make sparse
happy with using it.  Note that for this the return value has to be
double-inverted as the return value convention of lockref_put_or_lock
is inverted compared to _trylock conventions expected by __cond_lock,
as lockref_put_or_lock returns true when it did not need to take the
lock.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

All users of lockref_init() now initialize the count to 1, so hardcode
that and remove the count argument.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Link: https://lore.kernel.org/r/20250130135624.1899988-4-agruenba@redhat.com
Signed-off-by: Christian Brauner <brauner@kernel.org>

Add a helper to initialize the lockdep, that is initialize the spinlock
and set a value.  Having to open code them isn't a big deal, but having
an initializer feels right for a proper primitive.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20250115094702.504610-6-hch@lst.de
Signed-off-by: Christian Brauner <brauner@kernel.org>

Drop the superfluous externs from the remaining prototypes in lockref.h.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20250115094702.504610-5-hch@lst.de
Signed-off-by: Christian Brauner <brauner@kernel.org>

Replace int used as bool with the actual bool type for return values that
can only be true or false.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20250115094702.504610-4-hch@lst.de
Signed-off-by: Christian Brauner <brauner@kernel.org>

lockref_put_not_zero is not used anywhere, and unless I'm missing
something didn't end up being used used at all.  Remove it.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20250115094702.504610-2-hch@lst.de
Signed-off-by: Christian Brauner <brauner@kernel.org>

Looking at the conditional lock acquire functions in the kernel due to
the new sparse support (see commit 4a557a5d1a61 "sparse: introduce
conditional lock acquire function attribute"), it became obvious that
the lockref code has a couple of them, but they don't match the usual
naming convention for the other ones, and their return value logic is
also reversed.

In the other very similar places, the naming pattern is '*_and_lock()'
(eg 'atomic_put_and_lock()' and 'refcount_dec_and_lock()'), and the
function returns true when the lock is taken.

The lockref code is superficially very similar to the refcount code,
only with the special "atomic wrt the embedded lock" semantics.  But
instead of the '*_and_lock()' naming it uses '*_or_lock()'.

And instead of returning true in case it took the lock, it returns true
if it *didn't* take the lock.

Now, arguably the reflock code is quite logical: it really is a "either
decrement _or_ lock" kind of situation - and the return value is about
whether the operation succeeded without any special care needed.

So despite the similarities, the differences do make some sense, and
maybe it's not worth trying to unify the different conditional locking
primitives in this area.

But while looking at this all, it did become obvious that the
'lockref_get_or_lock()' function hasn't actually had any users for
almost a decade.

The only user it ever had was the shortlived 'd_rcu_to_refcount()'
function, and it got removed and replaced with 'lockref_get_not_dead()'
back in 2013 in commits 0d98439ea3c6 ("vfs: use lockred 'dead' flag to
mark unrecoverably dead dentries") and e5c832d55588 ("vfs: fix dentry
RCU to refcounting possibly sleeping dput()")

In fact, that single use was removed less than a week after the whole
function was introduced in commit b3abd80250c1 ("lockref: add
'lockref_get_or_lock() helper") so this function has been around for a
decade, but only had a user for six days.

Let's just put this mis-designed and unused function out of its misery.

We can think about the naming and semantic oddities of the remaining
'lockref_put_or_lock()' later, but at least that function has users.

And while the naming is different and the return value doesn't match,
that function matches the whole '{atomic,refcount}_dec_and_test()'
pattern much better (ie the magic happens when the count goes down to
zero, not when it is incremented from zero).

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Put a lockref unless the lockref is dead or its count would become zero.
This is the same as lockref_put_or_lock except that the lock is never
left held.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Signed-off-by: Bob Peterson <rpeterso@redhat.com>

Make __lockref_is_dead return bool due to this function only using either
true or false as its return value.

No functional change.

Link: http://lkml.kernel.org/r/1513266622-15860-3-git-send-email-baiyaowei@cmss.chinamobile.com
Signed-off-by: Yaowei Bai <baiyaowei@cmss.chinamobile.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>