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

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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: David Howells <dhowells@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lkml.kernel.org/r/20200729111120.GA2638@hirez.programming.kicks-ass.net
This commit is contained in:
Peter Zijlstra 2020-07-29 13:00:57 +02:00
parent 6eb6d05958
commit a435b9a143
1 changed files with 57 additions and 8 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

65
include/linux/refcount.h
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@ -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);
}
/**
@ -304,10 +343,20 @@ 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, int *oldp)
{
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)
{
if (unlikely(atomic_fetch_sub_release(1, &r->refs) <= 1))
refcount_warn_saturate(r, REFCOUNT_DEC_LEAK);
__refcount_dec(r, NULL);
}
extern __must_check bool refcount_dec_if_one(refcount_t *r);