[PATCH 5.4 60/87] locking/refcount: Define constants for saturation and max refcount values

Greg Kroah-Hartman
2022-07-27T16:43:29Z

From: Will Deacon <will@kernel.org>

[ Upstream commit 23e6b169c9917fbd77534f8c5f378cb073f548bd ]

The REFCOUNT_FULL implementation uses a different saturation point than
the x86 implementation, which means that the shared refcount code in
lib/refcount.c (e.g. refcount_dec_not_one()) needs to be aware of the
difference.

Rather than duplicate the definitions from the lkdtm driver, instead
move them into <linux/refcount.h> and update all references accordingly.

Signed-off-by: Will Deacon <will@kernel.org>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Tested-by: Hanjun Guo <guohanjun@huawei.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Elena Reshetova <elena.reshetova@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20191121115902.2551-2-will@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/misc/lkdtm/refcount.c | 8 --------
include/linux/refcount.h | 10 +++++++++-
lib/refcount.c | 37 +++++++++++++++++++----------------
3 files changed, 29 insertions(+), 26 deletions(-)

diff --git a/drivers/misc/lkdtm/refcount.c b/drivers/misc/lkdtm/refcount.c
index 0a146b32da13..abf3b7c1f686 100644
--- a/drivers/misc/lkdtm/refcount.c
+++ b/drivers/misc/lkdtm/refcount.c
@@ -6,14 +6,6 @@
#include "lkdtm.h"
#include <linux/refcount.h>

-#ifdef CONFIG_REFCOUNT_FULL
-#define REFCOUNT_MAX (UINT_MAX - 1)
-#define REFCOUNT_SATURATED UINT_MAX
-#else
-#define REFCOUNT_MAX INT_MAX
-#define REFCOUNT_SATURATED (INT_MIN / 2)
-#endif
-
static void overflow_check(refcount_t *ref)
{
switch (refcount_read(ref)) {
diff --git a/include/linux/refcount.h b/include/linux/refcount.h
index e28cce21bad6..79f62e8d2256 100644
--- a/include/linux/refcount.h
+++ b/include/linux/refcount.h
@@ -4,6 +4,7 @@

#include <linux/atomic.h>
#include <linux/compiler.h>
+#include <linux/limits.h>
#include <linux/spinlock_types.h>

struct mutex;
@@ -12,7 +13,7 @@ struct mutex;
* struct refcount_t - variant of atomic_t specialized for reference counts
* @refs: atomic_t counter field
*
- * The counter saturates at UINT_MAX and will not move once
+ * The counter saturates at REFCOUNT_SATURATED and will not move once
* there. This avoids wrapping the counter and causing 'spurious'
* use-after-free bugs.
*/
@@ -56,6 +57,9 @@ 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

@@ -68,6 +72,10 @@ extern void refcount_dec_checked(refcount_t *r);
#define refcount_dec refcount_dec_checked

#else
+
+#define REFCOUNT_MAX INT_MAX
+#define REFCOUNT_SATURATED (INT_MIN / 2)
+
# ifdef CONFIG_ARCH_HAS_REFCOUNT
# include <asm/refcount.h>
# else
diff --git a/lib/refcount.c b/lib/refcount.c
index 6e904af0fb3e..48b78a423d7d 100644
--- a/lib/refcount.c
+++ b/lib/refcount.c
@@ -5,8 +5,8 @@
* 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'
+ * It differs in that the counter saturates at REFCOUNT_SATURATED 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
@@ -48,7 +48,7 @@
* @i: the value to add to the refcount
* @r: the refcount
*
- * Will saturate at UINT_MAX and WARN.
+ * Will saturate at REFCOUNT_SATURATED 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
@@ -69,16 +69,17 @@ bool refcount_add_not_zero_checked(unsigned int i, refcount_t *r)
if (!val)
return false;

- if (unlikely(val == UINT_MAX))
+ if (unlikely(val == REFCOUNT_SATURATED))
return true;

new = val + i;
if (new < val)
- new = UINT_MAX;
+ new = REFCOUNT_SATURATED;

} while (!atomic_try_cmpxchg_relaxed(&r->refs, &val, new));

- WARN_ONCE(new == UINT_MAX, "refcount_t: saturated; leaking memory.\n");
+ WARN_ONCE(new == REFCOUNT_SATURATED,
+ "refcount_t: saturated; leaking memory.\n");

return true;
}
@@ -89,7 +90,7 @@ EXPORT_SYMBOL(refcount_add_not_zero_checked);
* @i: the value to add to the refcount
* @r: the refcount
*
- * Similar to atomic_add(), but will saturate at UINT_MAX and WARN.
+ * Similar to atomic_add(), but will saturate at REFCOUNT_SATURATED 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
@@ -110,7 +111,8 @@ EXPORT_SYMBOL(refcount_add_checked);
* refcount_inc_not_zero_checked - increment a refcount unless it is 0
* @r: the refcount to increment
*
- * Similar to atomic_inc_not_zero(), but will saturate at UINT_MAX and WARN.
+ * Similar to atomic_inc_not_zero(), but will saturate at REFCOUNT_SATURATED
+ * 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
@@ -133,7 +135,8 @@ bool refcount_inc_not_zero_checked(refcount_t *r)

} while (!atomic_try_cmpxchg_relaxed(&r->refs, &val, new));

- WARN_ONCE(new == UINT_MAX, "refcount_t: saturated; leaking memory.\n");
+ WARN_ONCE(new == REFCOUNT_SATURATED,
+ "refcount_t: saturated; leaking memory.\n");

return true;
}
@@ -143,7 +146,7 @@ EXPORT_SYMBOL(refcount_inc_not_zero_checked);
* refcount_inc_checked - increment a refcount
* @r: the refcount to increment
*
- * Similar to atomic_inc(), but will saturate at UINT_MAX and WARN.
+ * Similar to atomic_inc(), but will saturate at REFCOUNT_SATURATED and WARN.
*
* Provides no memory ordering, it is assumed the caller already has a
* reference on the object.
@@ -164,7 +167,7 @@ EXPORT_SYMBOL(refcount_inc_checked);
*
* Similar to atomic_dec_and_test(), but it will WARN, return false and
* ultimately leak on underflow and will fail to decrement when saturated
- * at UINT_MAX.
+ * at REFCOUNT_SATURATED.
*
* Provides release memory ordering, such that prior loads and stores are done
* before, and provides an acquire ordering on success such that free()
@@ -182,7 +185,7 @@ bool refcount_sub_and_test_checked(unsigned int i, refcount_t *r)
unsigned int new, val = atomic_read(&r->refs);

do {
- if (unlikely(val == UINT_MAX))
+ if (unlikely(val == REFCOUNT_SATURATED))
return false;

new = val - i;
@@ -207,7 +210,7 @@ EXPORT_SYMBOL(refcount_sub_and_test_checked);
* @r: the refcount
*
* Similar to atomic_dec_and_test(), it will WARN on underflow and fail to
- * decrement when saturated at UINT_MAX.
+ * decrement when saturated at REFCOUNT_SATURATED.
*
* Provides release memory ordering, such that prior loads and stores are done
* before, and provides an acquire ordering on success such that free()
@@ -226,7 +229,7 @@ EXPORT_SYMBOL(refcount_dec_and_test_checked);
* @r: the refcount
*
* Similar to atomic_dec(), it will WARN on underflow and fail to decrement
- * when saturated at UINT_MAX.
+ * when saturated at REFCOUNT_SATURATED.
*
* Provides release memory ordering, such that prior loads and stores are done
* before.
@@ -277,7 +280,7 @@ bool refcount_dec_not_one(refcount_t *r)
unsigned int new, val = atomic_read(&r->refs);

do {
- if (unlikely(val == UINT_MAX))
+ if (unlikely(val == REFCOUNT_SATURATED))
return true;

if (val == 1)
@@ -302,7 +305,7 @@ EXPORT_SYMBOL(refcount_dec_not_one);
* @lock: the mutex to be locked
*
* Similar to atomic_dec_and_mutex_lock(), it will WARN on underflow and fail
- * to decrement when saturated at UINT_MAX.
+ * to decrement when saturated at REFCOUNT_SATURATED.
*
* Provides release memory ordering, such that prior loads and stores are done
* before, and provides a control dependency such that free() must come after.
@@ -333,7 +336,7 @@ EXPORT_SYMBOL(refcount_dec_and_mutex_lock);
* @lock: the spinlock to be locked
*
* Similar to atomic_dec_and_lock(), it will WARN on underflow and fail to
- * decrement when saturated at UINT_MAX.
+ * decrement when saturated at REFCOUNT_SATURATED.
*
* Provides release memory ordering, such that prior loads and stores are done
* before, and provides a control dependency such that free() must come after.
--
2.35.1