diff options
author | Linus Torvalds <torvalds@linux-foundation.org> | 2017-02-28 10:44:16 -0800 |
---|---|---|
committer | Linus Torvalds <torvalds@linux-foundation.org> | 2017-02-28 10:44:16 -0800 |
commit | 74efe07bc38c538ba7ac40a895910f4f3bee3152 (patch) | |
tree | ab1eed83938e6f1358a40f3e72b0ae93a91dbd6c /include/linux/refcount.h | |
parent | e72e58faa709d554f95431dbafd3374db5ed3fbb (diff) | |
parent | 318b1dedcd39012624f466d281627553e9fa2570 (diff) | |
download | linux-stable-74efe07bc38c538ba7ac40a895910f4f3bee3152.tar.gz linux-stable-74efe07bc38c538ba7ac40a895910f4f3bee3152.tar.bz2 linux-stable-74efe07bc38c538ba7ac40a895910f4f3bee3152.zip |
Merge branch 'locking-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull locking fixes from Ingo Molnar:
"The main change is the uninlining of large refcount_t APIs, plus a
header dependency fix.
Note that the uninlining allowed us to enable the underflow/overflow
warnings unconditionally and remove the debug Kconfig switch: this
might trigger new warnings in buggy code and turn
crashes/use-after-free bugs into less harmful memory leaks"
* 'locking-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
locking/refcounts: Add missing kernel.h header to have UINT_MAX defined
locking/refcounts: Out-of-line everything
Diffstat (limited to 'include/linux/refcount.h')
-rw-r--r-- | include/linux/refcount.h | 278 |
1 files changed, 13 insertions, 265 deletions
diff --git a/include/linux/refcount.h b/include/linux/refcount.h index 600aadf9cca4..0023fee4bbbc 100644 --- a/include/linux/refcount.h +++ b/include/linux/refcount.h @@ -1,54 +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 <linux/atomic.h> -#include <linux/bug.h> #include <linux/mutex.h> #include <linux/spinlock.h> - -#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 +#include <linux/kernel.h> typedef struct refcount_struct { atomic_t refs; @@ -66,229 +22,21 @@ 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 */ |