locking/refcounts: Out-of-line everything (29dee3c0) · Commits · 戴 / test

include/linux/refcount.h

+12 −265

Original line number	Diff line number	Diff line
		#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;
		extern __must_check bool refcount_add_not_zero(unsigned int i, refcount_t *r);
		extern void refcount_add(unsigned int i, refcount_t *r);

		val = old;
		}
		extern __must_check bool refcount_inc_not_zero(refcount_t *r);
		extern void refcount_inc(refcount_t *r);

		return !new;
		}

		static inline __refcount_check
		bool refcount_dec_and_test(refcount_t *r)
		{
		return refcount_sub_and_test(1, 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");
		}
		extern __must_check bool refcount_sub_and_test(unsigned int i, refcount_t *r);
		extern void refcount_sub(unsigned int i, refcount_t *r);

		/*
		* 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);

		for (;;) {
		if (unlikely(val == UINT_MAX))
		return true;

		if (val == 1)
		return false;

		new = val - 1;
		if (new > val) {
		REFCOUNT_WARN(new > val, "refcount_t: underflow; use-after-free.\n");
		return true;
		}
		extern __must_check bool refcount_dec_and_test(refcount_t *r);
		extern void refcount_dec(refcount_t *r);

		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 */

lib/Kconfig.debug

+0 −13

Original line number	Diff line number	Diff line
		@@ -716,19 +716,6 @@ source "lib/Kconfig.kmemcheck"

		source "lib/Kconfig.kasan"

		config DEBUG_REFCOUNT
		bool "Verbose refcount checks"
		help
		Say Y here if you want reference counters (refcount_t and kref) to
		generate WARNs on dubious usage. Without this refcount_t will still
		be a saturating counter and avoid Use-After-Free by turning it into
		a resource leak Denial-Of-Service.

		Use of this option will increase kernel text size but will alert the
		admin of potential abuse.

		If in doubt, say "N".

		endmenu # "Memory Debugging"

		config ARCH_HAS_KCOV

lib/Makefile

+1 −1

Original line number	Diff line number	Diff line
		@@ -36,7 +36,7 @@ obj-y += bcd.o div64.o sort.o parser.o debug_locks.o random32.o \
		gcd.o lcm.o list_sort.o uuid.o flex_array.o iov_iter.o clz_ctz.o \
		bsearch.o find_bit.o llist.o memweight.o kfifo.o \
		percpu-refcount.o percpu_ida.o rhashtable.o reciprocal_div.o \
		once.o
		once.o refcount.o
		obj-y += string_helpers.o
		obj-$(CONFIG_TEST_STRING_HELPERS) += test-string_helpers.o
		obj-y += hexdump.o

lib/refcount.c

0 → 100644

+267 −0

Original line number	Diff line number	Diff line
		/*
		* 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/refcount.h>
		#include <linux/bug.h>

		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;
		}

		WARN(new == UINT_MAX, "refcount_t: saturated; leaking memory.\n");

		return true;
		}
		EXPORT_SYMBOL_GPL(refcount_add_not_zero);

		void refcount_add(unsigned int i, refcount_t *r)
		{
		WARN(!refcount_add_not_zero(i, r), "refcount_t: addition on 0; use-after-free.\n");
		}
		EXPORT_SYMBOL_GPL(refcount_add);

		/*
		* 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.
		*/
		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;
		}

		WARN(new == UINT_MAX, "refcount_t: saturated; leaking memory.\n");

		return true;
		}
		EXPORT_SYMBOL_GPL(refcount_inc_not_zero);

		/*
		* 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.
		*/
		void refcount_inc(refcount_t *r)
		{
		WARN(!refcount_inc_not_zero(r), "refcount_t: increment on 0; use-after-free.\n");
		}
		EXPORT_SYMBOL_GPL(refcount_inc);

		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) {
		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;
		}
		EXPORT_SYMBOL_GPL(refcount_sub_and_test);

		/*
		* 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.
		*/
		bool refcount_dec_and_test(refcount_t *r)
		{
		return refcount_sub_and_test(1, r);
		}
		EXPORT_SYMBOL_GPL(refcount_dec_and_test);

		/*
		* 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.
		*/

		void refcount_dec(refcount_t *r)
		{
		WARN(refcount_dec_and_test(r), "refcount_t: decrement hit 0; leaking memory.\n");
		}
		EXPORT_SYMBOL_GPL(refcount_dec);

		/*
		* 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.
		*/
		bool refcount_dec_if_one(refcount_t *r)
		{
		return atomic_cmpxchg_release(&r->refs, 1, 0) == 1;
		}
		EXPORT_SYMBOL_GPL(refcount_dec_if_one);

		/*
		* 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)
		*/
		bool refcount_dec_not_one(refcount_t *r)
		{
		unsigned int old, new, val = atomic_read(&r->refs);

		for (;;) {
		if (unlikely(val == UINT_MAX))
		return true;

		if (val == 1)
		return false;

		new = val - 1;
		if (new > val) {
		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;
		}
		EXPORT_SYMBOL_GPL(refcount_dec_not_one);

		/*
		* 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.
		*/
		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_GPL(refcount_dec_and_mutex_lock);

		/*
		* 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.
		*/
		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_GPL(refcount_dec_and_lock);

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