Commit a435b9a1 authored by Peter Zijlstra's avatar Peter Zijlstra
Browse files

locking/refcount: Provide __refcount API to obtain the old value 



David requested means to obtain the old/previous value from the
refcount API for tracing purposes.

Duplicate (most of) the API as __refcount*() with an additional
'int *' argument into which, if !NULL, the old value will be stored.

Requested-by: default avatarDavid Howells <dhowells@redhat.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarKees Cook <keescook@chromium.org>
Link: https://lkml.kernel.org/r/20200729111120.GA2638@hirez.programming.kicks-ass.net
parent 6eb6d059

include/linux/refcount.h

+57 −8
Original line number Diff line number Diff line
@@ -165,7 +165,7 @@ static inline unsigned int refcount_read(const refcount_t *r) 
 *

 * Return: false if the passed refcount is 0, true otherwise

 */

static inline __must_check bool refcount_add_not_zero(int i, refcount_t *r)

static inline __must_check bool __refcount_add_not_zero(int i, refcount_t *r, int *oldp)

{

	int old = refcount_read(r);
@@ -174,12 +174,20 @@ static inline __must_check bool refcount_add_not_zero(int i, refcount_t *r) 
			break;

	} while (!atomic_try_cmpxchg_relaxed(&r->refs, &old, old + i));



	if (oldp)

		*oldp = old;



	if (unlikely(old < 0 || old + i < 0))

		refcount_warn_saturate(r, REFCOUNT_ADD_NOT_ZERO_OVF);



	return old;

}



static inline __must_check bool refcount_add_not_zero(int i, refcount_t *r)

{

	return __refcount_add_not_zero(i, r, NULL);

}



/**

 * refcount_add - add a value to a refcount

 * @i: the value to add to the refcount
@@ -196,16 +204,24 @@ static inline __must_check bool refcount_add_not_zero(int i, refcount_t *r) 
 * cases, refcount_inc(), or one of its variants, should instead be used to

 * increment a reference count.

 */

static inline void refcount_add(int i, refcount_t *r)

static inline void __refcount_add(int i, refcount_t *r, int *oldp)

{

	int old = atomic_fetch_add_relaxed(i, &r->refs);



	if (oldp)

		*oldp = old;



	if (unlikely(!old))

		refcount_warn_saturate(r, REFCOUNT_ADD_UAF);

	else if (unlikely(old < 0 || old + i < 0))

		refcount_warn_saturate(r, REFCOUNT_ADD_OVF);

}



static inline void refcount_add(int i, refcount_t *r)

{

	__refcount_add(i, r, NULL);

}



/**

 * refcount_inc_not_zero - increment a refcount unless it is 0

 * @r: the refcount to increment
@@ -219,9 +235,14 @@ static inline void refcount_add(int i, refcount_t *r) 
 *

 * Return: true if the increment was successful, false otherwise

 */

static inline __must_check bool __refcount_inc_not_zero(refcount_t *r, int *oldp)

{

	return __refcount_add_not_zero(1, r, oldp);

}



static inline __must_check bool refcount_inc_not_zero(refcount_t *r)

{

	return refcount_add_not_zero(1, r);

	return __refcount_inc_not_zero(r, NULL);

}



/**
@@ -236,9 +257,14 @@ static inline __must_check bool refcount_inc_not_zero(refcount_t *r) 
 * Will WARN if the refcount is 0, as this represents a possible use-after-free

 * condition.

 */

static inline void __refcount_inc(refcount_t *r, int *oldp)

{

	__refcount_add(1, r, oldp);

}



static inline void refcount_inc(refcount_t *r)

{

	refcount_add(1, r);

	__refcount_inc(r, NULL);

}



/**
@@ -261,10 +287,13 @@ static inline void refcount_inc(refcount_t *r) 
 *

 * Return: true if the resulting refcount is 0, false otherwise

 */

static inline __must_check bool refcount_sub_and_test(int i, refcount_t *r)

static inline __must_check bool __refcount_sub_and_test(int i, refcount_t *r, int *oldp)

{

	int old = atomic_fetch_sub_release(i, &r->refs);



	if (oldp)

		*oldp = old;



	if (old == i) {

		smp_acquire__after_ctrl_dep();

		return true;
@@ -276,6 +305,11 @@ static inline __must_check bool refcount_sub_and_test(int i, refcount_t *r) 
	return false;

}



static inline __must_check bool refcount_sub_and_test(int i, refcount_t *r)

{

	return __refcount_sub_and_test(i, r, NULL);

}



/**

 * refcount_dec_and_test - decrement a refcount and test if it is 0

 * @r: the refcount
@@ -289,9 +323,14 @@ static inline __must_check bool refcount_sub_and_test(int i, refcount_t *r) 
 *

 * Return: true if the resulting refcount is 0, false otherwise

 */

static inline __must_check bool __refcount_dec_and_test(refcount_t *r, int *oldp)

{

	return __refcount_sub_and_test(1, r, oldp);

}



static inline __must_check bool refcount_dec_and_test(refcount_t *r)

{

	return refcount_sub_and_test(1, r);

	return __refcount_dec_and_test(r, NULL);

}



/**
@@ -304,12 +343,22 @@ static inline __must_check bool refcount_dec_and_test(refcount_t *r) 
 * Provides release memory ordering, such that prior loads and stores are done

 * before.

 */

static inline void refcount_dec(refcount_t *r)

static inline void __refcount_dec(refcount_t *r, int *oldp)

{

	if (unlikely(atomic_fetch_sub_release(1, &r->refs) <= 1))

	int old = atomic_fetch_sub_release(1, &r->refs);



	if (oldp)

		*oldp = old;



	if (unlikely(old <= 1))

		refcount_warn_saturate(r, REFCOUNT_DEC_LEAK);

}



static inline void refcount_dec(refcount_t *r)

{

	__refcount_dec(r, NULL);

}



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);

CRA Git | Maintained and supported by SUSTech CRA and CCSE