From 29dee3c03abce04cd527878ef5f9e5f91b7b83f4 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Fri, 10 Feb 2017 16:27:52 +0100 Subject: locking/refcounts: Out-of-line everything Linus asked to please make this real C code. And since size then isn't an issue what so ever anymore, remove the debug knob and make all WARN()s unconditional. Suggested-by: Linus Torvalds Signed-off-by: Peter Zijlstra (Intel) Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: dwindsor@gmail.com Cc: elena.reshetova@intel.com Cc: gregkh@linuxfoundation.org Cc: ishkamiel@gmail.com Cc: keescook@chromium.org Signed-off-by: Ingo Molnar --- include/linux/refcount.h | 277 ++--------------------------------------------- 1 file changed, 12 insertions(+), 265 deletions(-) (limited to 'include/linux/refcount.h') diff --git a/include/linux/refcount.h b/include/linux/refcount.h index 600aadf9cca4..0e8cfb2ce91e 100644 --- a/include/linux/refcount.h +++ b/include/linux/refcount.h @@ -1,55 +1,10 @@ #ifndef _LINUX_REFCOUNT_H #define _LINUX_REFCOUNT_H -/* - * 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 UINT_MAX 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(). - * - */ - #include -#include #include #include -#ifdef CONFIG_DEBUG_REFCOUNT -#define REFCOUNT_WARN(cond, str) WARN_ON(cond) -#define __refcount_check __must_check -#else -#define REFCOUNT_WARN(cond, str) (void)(cond) -#define __refcount_check -#endif - typedef struct refcount_struct { atomic_t refs; } refcount_t; @@ -66,229 +21,21 @@ static inline unsigned int refcount_read(const refcount_t *r) return atomic_read(&r->refs); } -static inline __refcount_check -bool refcount_add_not_zero(unsigned int i, refcount_t *r) -{ - unsigned int old, new, val = atomic_read(&r->refs); - - for (;;) { - if (!val) - return false; - - if (unlikely(val == UINT_MAX)) - return true; - - new = val + i; - if (new < val) - new = UINT_MAX; - old = atomic_cmpxchg_relaxed(&r->refs, val, new); - if (old == val) - break; - - val = old; - } - - REFCOUNT_WARN(new == UINT_MAX, "refcount_t: saturated; leaking memory.\n"); - - return true; -} - -static inline void refcount_add(unsigned int i, refcount_t *r) -{ - REFCOUNT_WARN(!refcount_add_not_zero(i, r), "refcount_t: addition on 0; use-after-free.\n"); -} - -/* - * 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. - */ -static inline __refcount_check -bool refcount_inc_not_zero(refcount_t *r) -{ - unsigned int old, new, val = atomic_read(&r->refs); - - for (;;) { - new = val + 1; - - if (!val) - return false; - - if (unlikely(!new)) - return true; - - old = atomic_cmpxchg_relaxed(&r->refs, val, new); - if (old == val) - break; - - val = old; - } - - REFCOUNT_WARN(new == UINT_MAX, "refcount_t: saturated; leaking memory.\n"); - - return true; -} - -/* - * 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. - */ -static inline void refcount_inc(refcount_t *r) -{ - REFCOUNT_WARN(!refcount_inc_not_zero(r), "refcount_t: increment on 0; use-after-free.\n"); -} - -/* - * 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. - */ -static inline __refcount_check -bool refcount_sub_and_test(unsigned int i, refcount_t *r) -{ - unsigned int old, new, val = atomic_read(&r->refs); - - for (;;) { - if (unlikely(val == UINT_MAX)) - return false; - - new = val - i; - if (new > val) { - REFCOUNT_WARN(new > val, "refcount_t: underflow; use-after-free.\n"); - return false; - } - - old = atomic_cmpxchg_release(&r->refs, val, new); - if (old == val) - break; - - val = old; - } - - return !new; -} - -static inline __refcount_check -bool refcount_dec_and_test(refcount_t *r) -{ - return refcount_sub_and_test(1, r); -} +extern __must_check bool refcount_add_not_zero(unsigned int i, refcount_t *r); +extern void refcount_add(unsigned int i, refcount_t *r); -/* - * Similar to atomic_dec(), 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. - */ -static inline -void refcount_dec(refcount_t *r) -{ - REFCOUNT_WARN(refcount_dec_and_test(r), "refcount_t: decrement hit 0; leaking memory.\n"); -} - -/* - * 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. - */ -static inline __refcount_check -bool refcount_dec_if_one(refcount_t *r) -{ - return atomic_cmpxchg_release(&r->refs, 1, 0) == 1; -} - -/* - * 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) - */ -static inline __refcount_check -bool refcount_dec_not_one(refcount_t *r) -{ - unsigned int old, new, val = atomic_read(&r->refs); +extern __must_check bool refcount_inc_not_zero(refcount_t *r); +extern void refcount_inc(refcount_t *r); - for (;;) { - if (unlikely(val == UINT_MAX)) - return true; +extern __must_check bool refcount_sub_and_test(unsigned int i, refcount_t *r); +extern void refcount_sub(unsigned int i, refcount_t *r); - if (val == 1) - return false; +extern __must_check bool refcount_dec_and_test(refcount_t *r); +extern void refcount_dec(refcount_t *r); - new = val - 1; - if (new > val) { - REFCOUNT_WARN(new > val, "refcount_t: underflow; use-after-free.\n"); - return true; - } - - old = atomic_cmpxchg_release(&r->refs, val, new); - if (old == val) - break; - - val = old; - } - - return true; -} - -/* - * 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. - */ -static inline __refcount_check -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; -} - -/* - * 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. - */ -static inline __refcount_check -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; -} +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); #endif /* _LINUX_REFCOUNT_H */ -- cgit