@@ -42,22 +42,51 @@
#include <linux/mutex.h>
#include <linux/spinlock.h>
+/**
+ * refcount_t - variant of atomic_t specialized for reference counts
+ * @refs: atomic_t counter field
+ *
+ * The counter saturates at UINT_MAX and will not move once
+ * there. This avoids wrapping the counter and causing 'spurious'
+ * use-after-free issues.
+ */
typedef struct refcount_struct {
atomic_t refs;
} refcount_t;
#define REFCOUNT_INIT(n) { .refs = ATOMIC_INIT(n), }
+/**
+ * refcount_set - set a refcount's internal counter
+ * @r: the refcount
+ * @n: value to which internal counter will be set
+ */
static inline void refcount_set(refcount_t *r, unsigned int n)
{
atomic_set(&r->refs, n);
}
+/**
+ * refcount_read - get a refcount's internal counter
+ * @r: the refcount
+ *
+ * Return: the value of the refcount's internal counter
+ */
static inline unsigned int refcount_read(const refcount_t *r)
{
return atomic_read(&r->refs);
}
+
+/**
+ * refcount_add_not_zero - add a value to a refcount unless the refcount is 0
+ * @i: the value to add to the refcount
+ * @r: the refcount
+ *
+ * Will saturate at UINT_MAX and WARN.
+ *
+ * Return: false if the refcount is 0, true otherwise.
+ */
static inline __must_check
bool refcount_add_not_zero(unsigned int i, refcount_t *r)
{
@@ -85,12 +114,17 @@ bool refcount_add_not_zero(unsigned int i, refcount_t *r)
return true;
}
-/*
+/**
+ * refcount_inc_not_zero - increment a refcount unless it is 0
+ * @r: the refcount to increment
+ *
* Similar to atomic_inc_not_zero(), will saturate at UINT_MAX and WARN.
*
* Provides no memory ordering, it is assumed the caller has guaranteed the
* object memory to be stable (RCU, etc.). It does provide a control dependency
* and thereby orders future stores. See the comment on top.
+ *
+ * Return: false if the refcount is 0, true otherwise
*/
static inline __must_check
bool refcount_inc_not_zero(refcount_t *r)
@@ -98,29 +132,49 @@ bool refcount_inc_not_zero(refcount_t *r)
return refcount_add_not_zero(1, r);
}
-/*
+/**
+ * refcount_inc - increment a refcount
+ * @r: the refcount to increment
+ *
* Similar to atomic_inc(), will saturate at UINT_MAX and WARN.
*
* Provides no memory ordering, it is assumed the caller already has a
* reference on the object, will WARN when this is not so.
+ *
+ * Will WARN if refcount is 0.
*/
static inline void refcount_inc(refcount_t *r)
{
WARN(!refcount_inc_not_zero(r), "refcount_t: increment on 0; use-after-free.\n");
}
+/**
+ * refcount_add - add a value to a refcount
+ * @i: the value to add to the refcount
+ * @r: the refcount
+ *
+ * Similar to atomic_add(), will saturate at UINT_MAX and WARN.
+ */
static inline void refcount_add(unsigned int i, refcount_t *r)
{
WARN(!refcount_add_not_zero(i, r), "refcount_t: addition on 0; use-after-free.\n");
}
-/*
+/**
+ * refcount_sub_and_test - subtract from a refcount and test if it is 0
+ * @i: amount to subtract from the refcount
+ * @r: the refcount
+ *
* Similar to atomic_dec_and_test(), it will WARN on underflow and fail to
* decrement when saturated at UINT_MAX.
*
* 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 if the resulting refcount is greater than 0, false if the
+ * resulting refcount is 0, the refcount's initial value is UINT_MAX
+ * or the subtraction operation causes an underflow.
*/
static inline __must_check
bool refcount_sub_and_test(unsigned int i, refcount_t *r)
@@ -145,13 +199,27 @@ bool refcount_sub_and_test(unsigned int i, refcount_t *r)
return !new;
}
+/**
+ * refcount_dec_and_test - decrement a refcount and test if it is 0
+ * @r: the refcount
+ *
+ * Similar to atomic_dec_and_test(), it will WARN on underflow and fail to
+ * decrement when saturated at UINT_MAX.
+ *
+ * Return: true if the resulting refcount is greater than 0, false if the
+ * resulting refcount is 0, the refcount's initial value is UINT_MAX
+ * or the decrement operation causes an underflow.
+ */
static inline __must_check
bool refcount_dec_and_test(refcount_t *r)
{
return refcount_sub_and_test(1, r);
}
-/*
+/**
+ * refcount_dec - decrement a refcount
+ * @r: the refcount
+ *
* Similar to atomic_dec(), it will WARN on underflow and fail to decrement
* when saturated at UINT_MAX.
*
@@ -164,7 +232,10 @@ void refcount_dec(refcount_t *r)
WARN(refcount_dec_and_test(r), "refcount_t: decrement hit 0; leaking memory.\n");
}
-/*
+/**
+ * refcount_dec_if_one - decrement a refcount if it is 1
+ * @r: the refcount
+ *
* No atomic_t counterpart, it attempts a 1 -> 0 transition and returns the
* success thereof.
*
@@ -174,6 +245,8 @@ void refcount_dec(refcount_t *r)
* It can be used like a try-delete operator; this explicit case is provided
* and not cmpxchg in generic, because that would allow implementing unsafe
* operations.
+ *
+ * Return: true if the refcount was decremented, false otherwise
*/
static inline __must_check
bool refcount_dec_if_one(refcount_t *r)
@@ -181,11 +254,16 @@ bool refcount_dec_if_one(refcount_t *r)
return atomic_cmpxchg_release(&r->refs, 1, 0) == 1;
}
-/*
+/**
+ * refcount_dec_not_one - decrement a refcount if it is not 1
+ * @r: the refcount
+ *
* No atomic_t counterpart, it decrements unless the value is 1, in which case
* it will return false.
*
* Was often done like: atomic_add_unless(&var, -1, 1)
+ *
+ * Return: false if the refcount was 1, true otherwise
*/
static inline __must_check
bool refcount_dec_not_one(refcount_t *r)
@@ -213,13 +291,21 @@ bool refcount_dec_not_one(refcount_t *r)
return true;
}
-/*
+/**
+ * refcount_dec_and_mutex_lock - return holding mutex if able to decrement
+ * refcount to 0
+ * @r: the refcount
+ * @lock: the mutex to be locked
+ *
* Similar to atomic_dec_and_mutex_lock(), it will WARN on underflow and fail
* to decrement when saturated at UINT_MAX.
*
* 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 lock if able to decrement refcount to 0, false
+ * otherwise
*/
static inline __must_check
bool refcount_dec_and_mutex_lock(refcount_t *r, struct mutex *lock)
@@ -236,13 +322,21 @@ bool refcount_dec_and_mutex_lock(refcount_t *r, struct mutex *lock)
return true;
}
-/*
+/**
+ * refcount_dec_and_lock - return holding spinlock if able to decrement
+ * refcount to 0
+ * @r: the refcount
+ * @lock: the spinlock to be locked
+ *
* Similar to atomic_dec_and_lock(), it will WARN on underflow and fail to
* decrement when saturated at UINT_MAX.
*
* 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 lock if able to decrement refcount to 0, false
+ * otherwise
*/
static inline __must_check
bool refcount_dec_and_lock(refcount_t *r, spinlock_t *lock)