Introduce kref_put_ww_mutex() helper that will handle the wait-wound
mutex auto-locking on kref_put(). This helper is wanted by DRM drivers
that extensively use dma-reservation locking which in turns uses ww-mutex.
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx>
---
include/linux/kref.h | 12 ++++++++++++
include/linux/refcount.h | 5 +++++
lib/refcount.c | 34 ++++++++++++++++++++++++++++++++++
3 files changed, 51 insertions(+)
diff --git a/include/linux/kref.h b/include/linux/kref.h
index d32e21a2538c..b2d8dc6e9ae0 100644
--- a/include/linux/kref.h
+++ b/include/linux/kref.h
@@ -90,6 +90,18 @@ static inline int kref_put_lock(struct kref *kref,
return 0;
}
+static inline int kref_put_ww_mutex(struct kref *kref,
+ void (*release)(struct kref *kref),
+ struct ww_mutex *lock,
+ struct ww_acquire_ctx *ctx)
+{
+ if (refcount_dec_and_ww_mutex_lock(&kref->refcount, lock, ctx)) {
+ release(kref);
+ return 1;
+ }
+ return 0;
+}
+
/**
* kref_get_unless_zero - Increment refcount for object unless it is zero.
* @kref: object.
diff --git a/include/linux/refcount.h b/include/linux/refcount.h
index a62fcca97486..be9ad272bc77 100644
--- a/include/linux/refcount.h
+++ b/include/linux/refcount.h
@@ -99,6 +99,8 @@
#include <linux/spinlock_types.h>
struct mutex;
+struct ww_mutex;
+struct ww_acquire_ctx;
/**
* typedef refcount_t - variant of atomic_t specialized for reference counts
@@ -366,4 +368,7 @@ 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 __must_check bool refcount_dec_and_ww_mutex_lock(refcount_t *r,
+ struct ww_mutex *lock,
+ struct ww_acquire_ctx *ctx) __cond_acquires(&lock->base);
#endif /* _LINUX_REFCOUNT_H */
diff --git a/lib/refcount.c b/lib/refcount.c
index a207a8f22b3c..3f6fd0ceed02 100644
--- a/lib/refcount.c
+++ b/lib/refcount.c
@@ -6,6 +6,7 @@
#include <linux/mutex.h>
#include <linux/refcount.h>
#include <linux/spinlock.h>
+#include <linux/ww_mutex.h>
#include <linux/bug.h>
#define REFCOUNT_WARN(str) WARN_ONCE(1, "refcount_t: " str ".\n")
@@ -184,3 +185,36 @@ bool refcount_dec_and_lock_irqsave(refcount_t *r, spinlock_t *lock,
return true;
}
EXPORT_SYMBOL(refcount_dec_and_lock_irqsave);
+
+/**
+ * refcount_dec_and_ww_mutex_lock - return holding ww-mutex if able to
+ * decrement refcount to 0
+ * @r: the refcount
+ * @lock: the ww-mutex to be locked
+ * @ctx: wait-wound context
+ *
+ * Similar to atomic_dec_and_lock(), it will WARN on underflow and fail to
+ * decrement when saturated at REFCOUNT_SATURATED.
+ *
+ * Provides release memory ordering, such that prior loads and stores are done
+ * before, and provides a control dependency such that free() must come after.
+ * See the comment on top.
+ *
+ * Return: true and hold ww-mutex lock if able to decrement refcount to 0,
+ * false otherwise
+ */
+bool refcount_dec_and_ww_mutex_lock(refcount_t *r, struct ww_mutex *lock,
+ struct ww_acquire_ctx *ctx)
+{
+ if (refcount_dec_not_one(r))
+ return false;
+
+ ww_mutex_lock(lock, ctx);
+ if (!refcount_dec_and_test(r)) {
+ ww_mutex_unlock(lock);
+ return false;
+ }
+
+ return true;
+}
+EXPORT_SYMBOL(refcount_dec_and_ww_mutex_lock);
--
2.41.0
