// SPDX-License-Identifier: GPL-2.0 /* * Out-of-line refcount functions. */ #include <linux/mutex.h> #include <linux/refcount.h> #include <linux/spinlock.h> #include <linux/bug.h> #define REFCOUNT_WARN(str) WARN_ONCE(1, "refcount_t: " str ".\n") void refcount_warn_saturate(refcount_t *r, enum refcount_saturation_type t) { refcount_set(r, REFCOUNT_SATURATED); switch (t) { case REFCOUNT_ADD_NOT_ZERO_OVF: REFCOUNT_WARN("saturated; leaking memory"); break; case REFCOUNT_ADD_OVF: REFCOUNT_WARN("saturated; leaking memory"); break; case REFCOUNT_ADD_UAF: REFCOUNT_WARN("addition on 0; use-after-free"); break; case REFCOUNT_SUB_UAF: REFCOUNT_WARN("underflow; use-after-free"); break; case REFCOUNT_DEC_LEAK: REFCOUNT_WARN("decrement hit 0; leaking memory"); break; default: REFCOUNT_WARN("unknown saturation event!?"); } } EXPORT_SYMBOL(refcount_warn_saturate); /** * 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. * * Like all decrement operations, it provides release memory order and provides * a control dependency. * * 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 resulting refcount is 0, false otherwise */ bool refcount_dec_if_one(refcount_t *r) { int val = 1; return atomic_try_cmpxchg_release(&r->refs, &val, 0); } EXPORT_SYMBOL(refcount_dec_if_one); /** * 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: true if the decrement operation was successful, false otherwise */ bool refcount_dec_not_one(refcount_t *r) { unsigned int new, val = atomic_read(&r->refs); do { if (unlikely(val == REFCOUNT_SATURATED)) return true; if (val == 1) return false; new = val - 1; if (new > val) { WARN_ONCE(new > val, "refcount_t: underflow; use-after-free.\n"); return true; } } while (!atomic_try_cmpxchg_release(&r->refs, &val, new)); return true; } EXPORT_SYMBOL(refcount_dec_not_one); /** * 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 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 mutex if able to decrement refcount to 0, false * otherwise */ bool refcount_dec_and_mutex_lock(refcount_t *r, struct mutex *lock) { if (refcount_dec_not_one(r)) return false; mutex_lock(lock); if (!refcount_dec_and_test(r)) { mutex_unlock(lock); return false; } return true; } EXPORT_SYMBOL(refcount_dec_and_mutex_lock); /** * 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 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 spinlock if able to decrement refcount to 0, false * otherwise */ bool refcount_dec_and_lock(refcount_t *r, spinlock_t *lock) { if (refcount_dec_not_one(r)) return false; spin_lock(lock); if (!refcount_dec_and_test(r)) { spin_unlock(lock); return false; } return true; } EXPORT_SYMBOL(refcount_dec_and_lock); /** * refcount_dec_and_lock_irqsave - return holding spinlock with disabled * interrupts if able to decrement refcount to 0 * @r: the refcount * @lock: the spinlock to be locked * @flags: saved IRQ-flags if the is acquired * * Same as refcount_dec_and_lock() above except that the spinlock is acquired * with disabled interupts. * * Return: true and hold spinlock if able to decrement refcount to 0, false * otherwise */ bool refcount_dec_and_lock_irqsave(refcount_t *r, spinlock_t *lock, unsigned long *flags) { if (refcount_dec_not_one(r)) return false; spin_lock_irqsave(lock, *flags); if (!refcount_dec_and_test(r)) { spin_unlock_irqrestore(lock, *flags); return false; } return true; } EXPORT_SYMBOL(refcount_dec_and_lock_irqsave);