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