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 <torvalds@linux-foundation.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
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 <mingo@kernel.org>

1 files changed, 12 insertions, 265 deletions

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 <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
-
 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 */