From 23e6b169c9917fbd77534f8c5f378cb073f548bd Mon Sep 17 00:00:00 2001
From: Will Deacon <will@kernel.org>
Date: Thu, 21 Nov 2019 11:58:53 +0000
Subject: locking/refcount: Define constants for saturation and max refcount
 values

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>
---
 include/linux/refcount.h | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

(limited to 'include/linux/refcount.h')

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
-- 
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