[PATCH v2 3/6] lib/refcount: Remove unused refcount_*_checked() variants

Will Deacon
2019-08-27T16:32:51Z

The full-fat refcount implementation is exposed via a set of functions
suffixed with "_checked()", the idea being that code can choose to use
the more expensive, yet more secure implementation on a case-by-case
basis.

In reality, this hasn't happened, so with a grand total of zero users,
let's remove the checked variants for now by simply dropping the suffix
and predicating the out-of-line functions on CONFIG_REFCOUNT_FULL=y.

Cc: Kees Cook <keescook@chromium.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Elena Reshetova <elena.reshetova@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Will Deacon <will@kernel.org>
---
include/linux/refcount.h | 25 +++++++---------------
lib/refcount.c | 54 ++++++++++++++++++++++++++----------------------
2 files changed, 36 insertions(+), 43 deletions(-)

diff --git a/include/linux/refcount.h b/include/linux/refcount.h
index 89066a1471dd..edd505d1a23b 100644
--- a/include/linux/refcount.h
+++ b/include/linux/refcount.h
@@ -44,32 +44,21 @@ static inline unsigned int refcount_read(const refcount_t *r)
return atomic_read(&r->refs);
}

-extern __must_check bool refcount_add_not_zero_checked(int i, refcount_t *r);
-extern void refcount_add_checked(int i, refcount_t *r);
-
-extern __must_check bool refcount_inc_not_zero_checked(refcount_t *r);
-extern void refcount_inc_checked(refcount_t *r);
-
-extern __must_check bool refcount_sub_and_test_checked(int i, refcount_t *r);
-
-extern __must_check bool refcount_dec_and_test_checked(refcount_t *r);
-extern void refcount_dec_checked(refcount_t *r);
-
#ifdef CONFIG_REFCOUNT_FULL

#define REFCOUNT_MAX (UINT_MAX - 1)
#define REFCOUNT_SATURATED UINT_MAX

-#define refcount_add_not_zero refcount_add_not_zero_checked
-#define refcount_add refcount_add_checked
+extern __must_check bool refcount_add_not_zero(int i, refcount_t *r);
+extern void refcount_add(int i, refcount_t *r);

-#define refcount_inc_not_zero refcount_inc_not_zero_checked
-#define refcount_inc refcount_inc_checked
+extern __must_check bool refcount_inc_not_zero(refcount_t *r);
+extern void refcount_inc(refcount_t *r);

-#define refcount_sub_and_test refcount_sub_and_test_checked
+extern __must_check bool refcount_sub_and_test(int i, refcount_t *r);

-#define refcount_dec_and_test refcount_dec_and_test_checked
-#define refcount_dec refcount_dec_checked
+extern __must_check bool refcount_dec_and_test(refcount_t *r);
+extern void refcount_dec(refcount_t *r);

#else

diff --git a/lib/refcount.c b/lib/refcount.c
index 719b0bc42ab1..a2f670998cee 100644
--- a/lib/refcount.c
+++ b/lib/refcount.c
@@ -43,8 +43,10 @@
#include <linux/spinlock.h>
#include <linux/bug.h>

+#ifdef CONFIG_REFCOUNT_FULL
+
/**
- * refcount_add_not_zero_checked - add a value to a refcount unless it is 0
+ * refcount_add_not_zero - add a value to a refcount unless it is 0
* @i: the value to add to the refcount
* @r: the refcount
*
@@ -61,7 +63,7 @@
*
* Return: false if the passed refcount is 0, true otherwise
*/
-bool refcount_add_not_zero_checked(int i, refcount_t *r)
+bool refcount_add_not_zero(int i, refcount_t *r)
{
unsigned int new, val = atomic_read(&r->refs);

@@ -83,10 +85,10 @@ bool refcount_add_not_zero_checked(int i, refcount_t *r)

return true;
}
-EXPORT_SYMBOL(refcount_add_not_zero_checked);
+EXPORT_SYMBOL(refcount_add_not_zero);

/**
- * refcount_add_checked - add a value to a refcount
+ * refcount_add - add a value to a refcount
* @i: the value to add to the refcount
* @r: the refcount
*
@@ -101,14 +103,14 @@ EXPORT_SYMBOL(refcount_add_not_zero_checked);
* cases, refcount_inc(), or one of its variants, should instead be used to
* increment a reference count.
*/
-void refcount_add_checked(int i, refcount_t *r)
+void refcount_add(int i, refcount_t *r)
{
- WARN_ONCE(!refcount_add_not_zero_checked(i, r), "refcount_t: addition on 0; use-after-free.\n");
+ WARN_ONCE(!refcount_add_not_zero(i, r), "refcount_t: addition on 0; use-after-free.\n");
}
-EXPORT_SYMBOL(refcount_add_checked);
+EXPORT_SYMBOL(refcount_add);

/**
- * refcount_inc_not_zero_checked - increment a refcount unless it is 0
+ * refcount_inc_not_zero - increment a refcount unless it is 0
* @r: the refcount to increment
*
* Similar to atomic_inc_not_zero(), but will saturate at REFCOUNT_SATURATED
@@ -120,7 +122,7 @@ EXPORT_SYMBOL(refcount_add_checked);
*
* Return: true if the increment was successful, false otherwise
*/
-bool refcount_inc_not_zero_checked(refcount_t *r)
+bool refcount_inc_not_zero(refcount_t *r)
{
unsigned int new, val = atomic_read(&r->refs);

@@ -140,10 +142,10 @@ bool refcount_inc_not_zero_checked(refcount_t *r)

return true;
}
-EXPORT_SYMBOL(refcount_inc_not_zero_checked);
+EXPORT_SYMBOL(refcount_inc_not_zero);

/**
- * refcount_inc_checked - increment a refcount
+ * refcount_inc - increment a refcount
* @r: the refcount to increment
*
* Similar to atomic_inc(), but will saturate at REFCOUNT_SATURATED and WARN.
@@ -154,14 +156,14 @@ EXPORT_SYMBOL(refcount_inc_not_zero_checked);
* Will WARN if the refcount is 0, as this represents a possible use-after-free
* condition.
*/
-void refcount_inc_checked(refcount_t *r)
+void refcount_inc(refcount_t *r)
{
- WARN_ONCE(!refcount_inc_not_zero_checked(r), "refcount_t: increment on 0; use-after-free.\n");
+ WARN_ONCE(!refcount_inc_not_zero(r), "refcount_t: increment on 0; use-after-free.\n");
}
-EXPORT_SYMBOL(refcount_inc_checked);
+EXPORT_SYMBOL(refcount_inc);

/**
- * refcount_sub_and_test_checked - subtract from a refcount and test if it is 0
+ * refcount_sub_and_test - subtract from a refcount and test if it is 0
* @i: amount to subtract from the refcount
* @r: the refcount
*
@@ -180,7 +182,7 @@ EXPORT_SYMBOL(refcount_inc_checked);
*
* Return: true if the resulting refcount is 0, false otherwise
*/
-bool refcount_sub_and_test_checked(int i, refcount_t *r)
+bool refcount_sub_and_test(int i, refcount_t *r)
{
unsigned int new, val = atomic_read(&r->refs);

@@ -203,10 +205,10 @@ bool refcount_sub_and_test_checked(int i, refcount_t *r)
return false;

}
-EXPORT_SYMBOL(refcount_sub_and_test_checked);
+EXPORT_SYMBOL(refcount_sub_and_test);

/**
- * refcount_dec_and_test_checked - decrement a refcount and test if it is 0
+ * refcount_dec_and_test - decrement a refcount and test if it is 0
* @r: the refcount
*
* Similar to atomic_dec_and_test(), it will WARN on underflow and fail to
@@ -218,14 +220,14 @@ EXPORT_SYMBOL(refcount_sub_and_test_checked);
*
* Return: true if the resulting refcount is 0, false otherwise
*/
-bool refcount_dec_and_test_checked(refcount_t *r)
+bool refcount_dec_and_test(refcount_t *r)
{
- return refcount_sub_and_test_checked(1, r);
+ return refcount_sub_and_test(1, r);
}
-EXPORT_SYMBOL(refcount_dec_and_test_checked);
+EXPORT_SYMBOL(refcount_dec_and_test);

/**
- * refcount_dec_checked - decrement a refcount
+ * refcount_dec - decrement a refcount
* @r: the refcount
*
* Similar to atomic_dec(), it will WARN on underflow and fail to decrement
@@ -234,11 +236,13 @@ EXPORT_SYMBOL(refcount_dec_and_test_checked);
* Provides release memory ordering, such that prior loads and stores are done
* before.
*/
-void refcount_dec_checked(refcount_t *r)
+void refcount_dec(refcount_t *r)
{
- WARN_ONCE(refcount_dec_and_test_checked(r), "refcount_t: decrement hit 0; leaking memory.\n");
+ WARN_ONCE(refcount_dec_and_test(r), "refcount_t: decrement hit 0; leaking memory.\n");
}
-EXPORT_SYMBOL(refcount_dec_checked);
+EXPORT_SYMBOL(refcount_dec);
+
+#endif /* CONFIG_REFCOUNT_FULL */

/**
* refcount_dec_if_one - decrement a refcount if it is 1
--
2.11.0