[RFC 1/2] refcount: introduce generic lockptr funcs

[RFC 1/2] refcount: introduce generic lockptr funcs

[Alexander Aring]

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

[RFC 2/2] kref: introduce kref_put_lockptr() and use lockptr

[Alexander Aring]

This patch switches to make kref_put_lock() more locktype independend by
introducing kref_put_lockptr() and using refcount_dec_and_lockptr(). The
user can now pass a lockptr and do the specific locktype operation by
parameters. The current kref_put_mutex() and kref_put_lock() has been
adapted to use the new kref_put_lockptr() implementation for existing
users.

Signed-off-by: Alexander Aring <aahringo@redhat.com>
---
 include/linux/kref.h | 25 ++++++++++++++++---------
 1 file changed, 16 insertions(+), 9 deletions(-)

diff --git a/include/linux/kref.h b/include/linux/kref.h
index d32e21a2538c..09bc79435dbb 100644
--- a/include/linux/kref.h
+++ b/include/linux/kref.h
@@ -68,26 +68,33 @@ static inline int kref_put(struct kref *kref, void (*release)(struct kref *kref)
 	return 0;
 }
 
-static inline int kref_put_mutex(struct kref *kref,
-				 void (*release)(struct kref *kref),
-				 struct mutex *lock)
+static inline int kref_put_lockptr(struct kref *kref,
+				   void (*release)(struct kref *kref),
+				   void (*lock)(void *lockptr),
+				   void (*unlock)(void *lockptr),
+				   void *lockptr)
 {
-	if (refcount_dec_and_mutex_lock(&kref->refcount, lock)) {
+	if (refcount_dec_and_lockptr(&kref->refcount, lock, unlock, lockptr)) {
 		release(kref);
 		return 1;
 	}
 	return 0;
 }
 
+static inline int kref_put_mutex(struct kref *kref,
+				 void (*release)(struct kref *kref),
+				 struct mutex *lock)
+{
+	return kref_put_lockptr(kref, release, lockptr_mutex_lock,
+				lockptr_mutex_unlock, lock);
+}
+
 static inline int kref_put_lock(struct kref *kref,
 				void (*release)(struct kref *kref),
 				spinlock_t *lock)
 {
-	if (refcount_dec_and_lock(&kref->refcount, lock)) {
-		release(kref);
-		return 1;
-	}
-	return 0;
+	return kref_put_lockptr(kref, release, lockptr_spin_lock,
+				lockptr_spin_unlock, lock);
 }
 
 /**
-- 
2.39.3

Re: [RFC 1/2] refcount: introduce generic lockptr funcs

[Peter Zijlstra]

On Fri, Nov 03, 2023 at 12:16:34PM -0400, Alexander Aring wrote:

> 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);

This is terrible, you're forcing indirect calls on everything.

Re: [RFC 1/2] refcount: introduce generic lockptr funcs

[Alexander Aring]

Hi,

On Fri, Nov 3, 2023 at 2:54 PM Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Fri, Nov 03, 2023 at 12:16:34PM -0400, Alexander Aring wrote:
>
> > 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);
>
> This is terrible, you're forcing indirect calls on everything.
>

Okay, I see. How about introducing a macro producing all the code at
preprocessor time?

- Alex

Re: [RFC 1/2] refcount: introduce generic lockptr funcs

[Peter Zijlstra]

On Fri, Nov 03, 2023 at 03:20:08PM -0400, Alexander Aring wrote:
> Hi,
> 
> On Fri, Nov 3, 2023 at 2:54 PM Peter Zijlstra <peterz@infradead.org> wrote:
> >
> > On Fri, Nov 03, 2023 at 12:16:34PM -0400, Alexander Aring wrote:
> >
> > > 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);
> >
> > This is terrible, you're forcing indirect calls on everything.
> >
> 
> Okay, I see. How about introducing a macro producing all the code at
> preprocessor time?

__always_inline should work, then you get constant propagation for the
function pointer.

But indeed, perhaps a macro is more convenient vs the irq flags
argument. You'll then end up with something like:

#define __refcount_dec_and_lock(_ref, _lock, _unlock) \
({ 	bool _ret = false; \
	if (!refcount_dec_not_one(_ref)) { \
		_lock; \
		if (!refcount_dec_and_test(_ref)) { \
			_unlock; \
		} else { \
			_ret = true; \
		} \
	} \
	_ret; \
})


bool refcount_dec_and_spinlock_irqsave(refcount_t *r, spinlock_t *lock, 
				       unsigned long *flags)
{
	return __refcount_dec_and_lock(r, spin_lock_irqsave(*lock, *flags),
					  spin_unlock_irqrestore(*lock, *flags));
}

Re: [RFC 1/2] refcount: introduce generic lockptr funcs

[Alexander Aring]

Hi,

On Mon, Nov 6, 2023 at 6:11 AM Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Fri, Nov 03, 2023 at 03:20:08PM -0400, Alexander Aring wrote:
> > Hi,
> >
> > On Fri, Nov 3, 2023 at 2:54 PM Peter Zijlstra <peterz@infradead.org> wrote:
> > >
> > > On Fri, Nov 03, 2023 at 12:16:34PM -0400, Alexander Aring wrote:
> > >
> > > > 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);
> > >
> > > This is terrible, you're forcing indirect calls on everything.
> > >
> >
> > Okay, I see. How about introducing a macro producing all the code at
> > preprocessor time?
>
> __always_inline should work, then you get constant propagation for the
> function pointer.
>

Thanks, it is always good to learn something new.

> But indeed, perhaps a macro is more convenient vs the irq flags
> argument. You'll then end up with something like:
>
> #define __refcount_dec_and_lock(_ref, _lock, _unlock) \
> ({      bool _ret = false; \
>         if (!refcount_dec_not_one(_ref)) { \
>                 _lock; \
>                 if (!refcount_dec_and_test(_ref)) { \
>                         _unlock; \
>                 } else { \
>                         _ret = true; \
>                 } \
>         } \
>         _ret; \
> })
>
>
> bool refcount_dec_and_spinlock_irqsave(refcount_t *r, spinlock_t *lock,
>                                        unsigned long *flags)
> {
>         return __refcount_dec_and_lock(r, spin_lock_irqsave(*lock, *flags),
>                                           spin_unlock_irqrestore(*lock, *flags));
> }

I was thinking of solving the additional flags parameter with
prototype and argos macros e.g. TRACE_EVENT() is doing it, but this
version looks much better.
I will send a patch and do similar things with _kref_put_lock().

- Alex

[RFC 1/2] refcount: introduce generic lockptr funcs

[Alexander Aring]

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

Re: [RFC 1/2] refcount: introduce generic lockptr funcs

[Alexander Aring]

Hi,

On Fri, Nov 3, 2023 at 12:07 PM Alexander Aring <aahringo@redhat.com> wrote:
>
> 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.

just an RFC to check if there is any interest to introduce something
like this. I think the idea is clear. My current use case is to have
rwlock_t and its bh lock operations using something like
refcount_dec_and_write_lock_bh() and later kref_put_write_lock_bh(). I
try to avoid copying some copy code again. I am open to any better
design change. Or telling me to just duplicate code again for what I
need it for. However this has the advantage that somebody can use
their "own" locktype implementation out of kernel core code.

Thanks.

- Alex

Re: [RFC 1/2] refcount: introduce generic lockptr funcs

[Alexander Aring]

Hi,

On Fri, Nov 3, 2023 at 12:14 PM Alexander Aring <aahringo@redhat.com> wrote:
>
> Hi,
>
> On Fri, Nov 3, 2023 at 12:07 PM Alexander Aring <aahringo@redhat.com> wrote:
> >
> > 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.
>
> just an RFC to check if there is any interest to introduce something
> like this. I think the idea is clear. My current use case is to have
> rwlock_t and its bh lock operations using something like
> refcount_dec_and_write_lock_bh() and later kref_put_write_lock_bh(). I
> try to avoid copying some copy code again. I am open to any better
> design change. Or telling me to just duplicate code again for what I
> need it for. However this has the advantage that somebody can use
> their "own" locktype implementation out of kernel core code.

I will resubmit this RFC series because I forgot to cc the linux
kernel mailing list that indeed makes sense here.

- Alex