| /* SPDX-License-Identifier: GPL-2.0 */ |
| #ifndef _LINUX_REFCOUNT_H |
| #define _LINUX_REFCOUNT_H |
| |
| #include <linux/atomic.h> |
| #include <linux/compiler.h> |
| #include <linux/limits.h> |
| #include <linux/spinlock_types.h> |
| |
| struct mutex; |
| |
| /** |
| * struct refcount_t - variant of atomic_t specialized for reference counts |
| * @refs: atomic_t counter field |
| * |
| * The counter saturates at REFCOUNT_SATURATED and will not move once |
| * there. This avoids wrapping the counter and causing 'spurious' |
| * use-after-free bugs. |
| */ |
| typedef struct refcount_struct { |
| atomic_t refs; |
| } refcount_t; |
| |
| #define REFCOUNT_INIT(n) { .refs = ATOMIC_INIT(n), } |
| |
| /** |
| * refcount_set - set a refcount's value |
| * @r: the refcount |
| * @n: value to which the refcount will be set |
| */ |
| static inline void refcount_set(refcount_t *r, int n) |
| { |
| atomic_set(&r->refs, n); |
| } |
| |
| /** |
| * refcount_read - get a refcount's value |
| * @r: the refcount |
| * |
| * Return: the refcount's value |
| */ |
| static inline unsigned int refcount_read(const refcount_t *r) |
| { |
| return atomic_read(&r->refs); |
| } |
| |
| #ifdef CONFIG_REFCOUNT_FULL |
| #include <linux/bug.h> |
| |
| #define REFCOUNT_MAX (UINT_MAX - 1) |
| #define REFCOUNT_SATURATED UINT_MAX |
| |
| /* |
| * Variant of atomic_t specialized for reference counts. |
| * |
| * The interface matches the atomic_t interface (to aid in porting) but only |
| * provides the few functions one should use for reference counting. |
| * |
| * It differs in that the counter saturates at REFCOUNT_SATURATED and will not |
| * move once there. This avoids wrapping the counter and causing 'spurious' |
| * use-after-free issues. |
| * |
| * Memory ordering rules are slightly relaxed wrt regular atomic_t functions |
| * and provide only what is strictly required for refcounts. |
| * |
| * The increments are fully relaxed; these will not provide ordering. The |
| * rationale is that whatever is used to obtain the object we're increasing the |
| * reference count on will provide the ordering. For locked data structures, |
| * its the lock acquire, for RCU/lockless data structures its the dependent |
| * load. |
| * |
| * Do note that inc_not_zero() provides a control dependency which will order |
| * future stores against the inc, this ensures we'll never modify the object |
| * if we did not in fact acquire a reference. |
| * |
| * The decrements will provide release order, such that all the prior loads and |
| * stores will be issued before, it also provides a control dependency, which |
| * will order us against the subsequent free(). |
| * |
| * The control dependency is against the load of the cmpxchg (ll/sc) that |
| * succeeded. This means the stores aren't fully ordered, but this is fine |
| * because the 1->0 transition indicates no concurrency. |
| * |
| * Note that the allocator is responsible for ordering things between free() |
| * and alloc(). |
| * |
| * The decrements dec_and_test() and sub_and_test() also provide acquire |
| * ordering on success. |
| * |
| */ |
| |
| /** |
| * refcount_add_not_zero - add a value to a refcount unless it is 0 |
| * @i: the value to add to the refcount |
| * @r: the refcount |
| * |
| * Will saturate at REFCOUNT_SATURATED 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. |
| * |
| * Use of this function is not recommended for the normal reference counting |
| * use case in which references are taken and released one at a time. In these |
| * cases, refcount_inc(), or one of its variants, should instead be used to |
| * increment a reference count. |
| * |
| * Return: false if the passed refcount is 0, true otherwise |
| */ |
| static inline __must_check bool refcount_add_not_zero(int i, refcount_t *r) |
| { |
| unsigned int new, val = atomic_read(&r->refs); |
| |
| do { |
| if (!val) |
| return false; |
| |
| if (unlikely(val == REFCOUNT_SATURATED)) |
| return true; |
| |
| new = val + i; |
| if (new < val) |
| new = REFCOUNT_SATURATED; |
| |
| } while (!atomic_try_cmpxchg_relaxed(&r->refs, &val, new)); |
| |
| WARN_ONCE(new == REFCOUNT_SATURATED, |
| "refcount_t: saturated; leaking memory.\n"); |
| |
| return true; |
| } |
| |
| /** |
| * refcount_add - add a value to a refcount |
| * @i: the value to add to the refcount |
| * @r: the refcount |
| * |
| * Similar to atomic_add(), but will saturate at REFCOUNT_SATURATED 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. |
| * |
| * Use of this function is not recommended for the normal reference counting |
| * use case in which references are taken and released one at a time. In these |
| * cases, refcount_inc(), or one of its variants, should instead be used to |
| * increment a reference count. |
| */ |
| static inline void refcount_add(int i, refcount_t *r) |
| { |
| WARN_ONCE(!refcount_add_not_zero(i, r), "refcount_t: addition on 0; use-after-free.\n"); |
| } |
| |
| /** |
| * refcount_inc_not_zero - increment a refcount unless it is 0 |
| * @r: the refcount to increment |
| * |
| * Similar to atomic_inc_not_zero(), but will saturate at REFCOUNT_SATURATED |
| * 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: true if the increment was successful, false otherwise |
| */ |
| static inline __must_check bool refcount_inc_not_zero(refcount_t *r) |
| { |
| unsigned int new, val = atomic_read(&r->refs); |
| |
| do { |
| new = val + 1; |
| |
| if (!val) |
| return false; |
| |
| if (unlikely(!new)) |
| return true; |
| |
| } while (!atomic_try_cmpxchg_relaxed(&r->refs, &val, new)); |
| |
| WARN_ONCE(new == REFCOUNT_SATURATED, |
| "refcount_t: saturated; leaking memory.\n"); |
| |
| return true; |
| } |
| |
| /** |
| * refcount_inc - increment a refcount |
| * @r: the refcount to increment |
| * |
| * Similar to atomic_inc(), but will saturate at REFCOUNT_SATURATED and WARN. |
| * |
| * Provides no memory ordering, it is assumed the caller already has a |
| * reference on the object. |
| * |
| * Will WARN if the refcount is 0, as this represents a possible use-after-free |
| * condition. |
| */ |
| static inline void refcount_inc(refcount_t *r) |
| { |
| WARN_ONCE(!refcount_inc_not_zero(r), "refcount_t: increment 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(), but it will WARN, return false and |
| * ultimately leak on underflow and will fail to decrement when saturated |
| * at REFCOUNT_SATURATED. |
| * |
| * Provides release memory ordering, such that prior loads and stores are done |
| * before, and provides an acquire ordering on success such that free() |
| * must come after. |
| * |
| * Use of this function is not recommended for the normal reference counting |
| * use case in which references are taken and released one at a time. In these |
| * cases, refcount_dec(), or one of its variants, should instead be used to |
| * decrement a reference count. |
| * |
| * Return: true if the resulting refcount is 0, false otherwise |
| */ |
| static inline __must_check bool refcount_sub_and_test(int i, refcount_t *r) |
| { |
| unsigned int new, val = atomic_read(&r->refs); |
| |
| do { |
| if (unlikely(val == REFCOUNT_SATURATED)) |
| return false; |
| |
| new = val - i; |
| if (new > val) { |
| WARN_ONCE(new > val, "refcount_t: underflow; use-after-free.\n"); |
| return false; |
| } |
| |
| } while (!atomic_try_cmpxchg_release(&r->refs, &val, new)); |
| |
| if (!new) { |
| smp_acquire__after_ctrl_dep(); |
| return true; |
| } |
| return false; |
| |
| } |
| |
| /** |
| * 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 REFCOUNT_SATURATED. |
| * |
| * Provides release memory ordering, such that prior loads and stores are done |
| * before, and provides an acquire ordering on success such that free() |
| * must come after. |
| * |
| * Return: true if the resulting refcount is 0, false otherwise |
| */ |
| 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 REFCOUNT_SATURATED. |
| * |
| * Provides release memory ordering, such that prior loads and stores are done |
| * before. |
| */ |
| static inline void refcount_dec(refcount_t *r) |
| { |
| WARN_ONCE(refcount_dec_and_test(r), "refcount_t: decrement hit 0; leaking memory.\n"); |
| } |
| |
| #else /* CONFIG_REFCOUNT_FULL */ |
| |
| #define REFCOUNT_MAX INT_MAX |
| #define REFCOUNT_SATURATED (INT_MIN / 2) |
| |
| # ifdef CONFIG_ARCH_HAS_REFCOUNT |
| # include <asm/refcount.h> |
| # else |
| static inline __must_check bool refcount_add_not_zero(int i, refcount_t *r) |
| { |
| return atomic_add_unless(&r->refs, i, 0); |
| } |
| |
| static inline void refcount_add(int i, refcount_t *r) |
| { |
| atomic_add(i, &r->refs); |
| } |
| |
| static inline __must_check bool refcount_inc_not_zero(refcount_t *r) |
| { |
| return atomic_add_unless(&r->refs, 1, 0); |
| } |
| |
| static inline void refcount_inc(refcount_t *r) |
| { |
| atomic_inc(&r->refs); |
| } |
| |
| static inline __must_check bool refcount_sub_and_test(int i, refcount_t *r) |
| { |
| return atomic_sub_and_test(i, &r->refs); |
| } |
| |
| static inline __must_check bool refcount_dec_and_test(refcount_t *r) |
| { |
| return atomic_dec_and_test(&r->refs); |
| } |
| |
| static inline void refcount_dec(refcount_t *r) |
| { |
| atomic_dec(&r->refs); |
| } |
| # endif /* !CONFIG_ARCH_HAS_REFCOUNT */ |
| #endif /* !CONFIG_REFCOUNT_FULL */ |
| |
| extern __must_check bool refcount_dec_if_one(refcount_t *r); |
| extern __must_check bool refcount_dec_not_one(refcount_t *r); |
| extern __must_check bool refcount_dec_and_mutex_lock(refcount_t *r, struct mutex *lock); |
| 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); |
| #endif /* _LINUX_REFCOUNT_H */ |