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From:   Alexander Aring <aahringo@redhat.com>
To:     will@kernel.org
Cc:     gfs2@lists.linux.dev, aahringo@redhat.com, peterz@infradead.org,
        boqun.feng@gmail.com, mark.rutland@arm.com,
        linux-kernel@vger.kernel.org
Subject: [RFC 1/2] refcount: introduce generic lockptr funcs
Date:   Fri,  3 Nov 2023 12:16:34 -0400
Message-Id: <20231103161635.1902667-1-aahringo@redhat.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

This patch introduce lockptr refcount operations. Currently refcount has
a lot of refcount_dec_and_lock() functionality for most common used
locktype. Those functions look mostly all the same and is duplicated
inside the refcount implementation. Instead of introducing a new whole
refcount_dec_and_lock() functionality e.g. for rwlock_t and their _bh
variants this patch will introduce lockptr. A lockptr is just a void *
and refers to the actual locking instance that can even be an own
locking type. Over the passed callbacks for lock and unlock operations
the void *lockptr becomes to the real thing by casting it and do the
locktype specific lock operation.

Signed-off-by: Alexander Aring <aahringo@redhat.com>
---
 include/linux/refcount.h | 15 +++++++
 lib/refcount.c           | 92 ++++++++++++++++++++++++++++------------
 2 files changed, 80 insertions(+), 27 deletions(-)

diff --git a/include/linux/refcount.h b/include/linux/refcount.h
index a62fcca97486..7b1fb85212cc 100644
--- a/include/linux/refcount.h
+++ b/include/linux/refcount.h
@@ -366,4 +366,19 @@ extern __must_check bool refcount_dec_and_lock(refcount_t *r, spinlock_t *lock)
 extern __must_check bool refcount_dec_and_lock_irqsave(refcount_t *r,
 						       spinlock_t *lock,
 						       unsigned long *flags) __cond_acquires(lock);
+extern bool refcount_dec_and_lockptr(refcount_t *r, void (*lock)(void *lockptr),
+				     void (*unlock)(void *lockptr),  void *lockptr) __cond_acquires(lockptr);
+
+extern void lockptr_mutex_lock(void *lockptr) __acquires(lockptr);
+extern void lockptr_mutex_unlock(void *lockptr) __releases(lockptr);
+extern void lockptr_spin_lock(void *lockptr) __acquires(lockptr);
+extern void lockptr_spin_unlock(void *lockptr) __releases(lockptr);
+
+struct lockptr_irqsave_data {
+	void *lockptr;
+	unsigned long *flags;
+};
+extern void lockptr_irqsave(void *lockptr) __acquires(lockptr);
+extern void lockptr_irqsave(void *lockptr) __releases(lockptr);
+
 #endif /* _LINUX_REFCOUNT_H */
diff --git a/lib/refcount.c b/lib/refcount.c
index a207a8f22b3c..e28678f0f473 100644
--- a/lib/refcount.c
+++ b/lib/refcount.c
@@ -94,6 +94,34 @@ bool refcount_dec_not_one(refcount_t *r)
 }
 EXPORT_SYMBOL(refcount_dec_not_one);
 
+bool refcount_dec_and_lockptr(refcount_t *r, void (*lock)(void *lockptr),
+			      void (*unlock)(void *lockptr),  void *lockptr)
+{
+	if (refcount_dec_not_one(r))
+		return false;
+
+	lock(lockptr);
+	if (!refcount_dec_and_test(r)) {
+		unlock(lockptr);
+		return false;
+	}
+
+	return true;
+}
+EXPORT_SYMBOL(refcount_dec_and_lockptr);
+
+void lockptr_mutex_lock(void *lockptr)
+{
+	mutex_lock(lockptr);
+}
+EXPORT_SYMBOL(lockptr_mutex_lock);
+
+void lockptr_mutex_unlock(void *lockptr)
+{
+	mutex_unlock(lockptr);
+}
+EXPORT_SYMBOL(lockptr_mutex_unlock);
+
 /**
  * refcount_dec_and_mutex_lock - return holding mutex if able to decrement
  *                               refcount to 0
@@ -112,18 +140,22 @@ EXPORT_SYMBOL(refcount_dec_not_one);
  */
 bool refcount_dec_and_mutex_lock(refcount_t *r, struct mutex *lock)
 {
-	if (refcount_dec_not_one(r))
-		return false;
+	return refcount_dec_and_lockptr(r, lockptr_mutex_lock,
+					lockptr_mutex_unlock, lock);
+}
+EXPORT_SYMBOL(refcount_dec_and_mutex_lock);
 
-	mutex_lock(lock);
-	if (!refcount_dec_and_test(r)) {
-		mutex_unlock(lock);
-		return false;
-	}
+void lockptr_spin_lock(void *lockptr)
+{
+	spin_lock(lockptr);
+}
+EXPORT_SYMBOL(lockptr_spin_lock);
 
-	return true;
+void lockptr_spin_unlock(void *lockptr)
+{
+	spin_unlock(lockptr);
 }
-EXPORT_SYMBOL(refcount_dec_and_mutex_lock);
+EXPORT_SYMBOL(lockptr_spin_unlock);
 
 /**
  * refcount_dec_and_lock - return holding spinlock if able to decrement
@@ -143,18 +175,26 @@ EXPORT_SYMBOL(refcount_dec_and_mutex_lock);
  */
 bool refcount_dec_and_lock(refcount_t *r, spinlock_t *lock)
 {
-	if (refcount_dec_not_one(r))
-		return false;
+	return refcount_dec_and_lockptr(r, lockptr_spin_lock,
+					lockptr_spin_unlock, lock);
+}
+EXPORT_SYMBOL(refcount_dec_and_lock);
 
-	spin_lock(lock);
-	if (!refcount_dec_and_test(r)) {
-		spin_unlock(lock);
-		return false;
-	}
+void lockptr_lock_irqsave(void *lockptr)
+{
+	struct lockptr_irqsave_data *d = lockptr;
 
-	return true;
+	spin_lock_irqsave(d->lockptr, *d->flags);
 }
-EXPORT_SYMBOL(refcount_dec_and_lock);
+EXPORT_SYMBOL(lockptr_lock_irqsave);
+
+void lockptr_unlock_irqsave(void *lockptr)
+{
+	struct lockptr_irqsave_data *d = lockptr;
+
+	spin_unlock_irqrestore(d->lockptr, *d->flags);
+}
+EXPORT_SYMBOL(lockptr_unlock_irqsave);
 
 /**
  * refcount_dec_and_lock_irqsave - return holding spinlock with disabled
@@ -172,15 +212,13 @@ EXPORT_SYMBOL(refcount_dec_and_lock);
 bool refcount_dec_and_lock_irqsave(refcount_t *r, spinlock_t *lock,
 				   unsigned long *flags)
 {
-	if (refcount_dec_not_one(r))
-		return false;
+	struct lockptr_irqsave_data d = {
+		.lockptr = lock,
+		.flags = flags,
+	};
 
-	spin_lock_irqsave(lock, *flags);
-	if (!refcount_dec_and_test(r)) {
-		spin_unlock_irqrestore(lock, *flags);
-		return false;
-	}
-
-	return true;
+	return refcount_dec_and_lockptr(r, lockptr_lock_irqsave,
+					lockptr_unlock_irqsave, &d);
 }
 EXPORT_SYMBOL(refcount_dec_and_lock_irqsave);
+
-- 
2.39.3