locking/refcount: Ensure integer operands are treated as signed

In preparation for changing the saturation point of REFCOUNT_FULL to
INT_MIN/2, change the type of integer operands passed into the API
from 'unsigned int' to 'int' so that we can avoid casting during
comparisons when we don't want to fall foul of C integral conversion
rules for signed and unsigned types.

Since the kernel is compiled with '-fno-strict-overflow', we don't need
to worry about the UB introduced by signed overflow here. Furthermore,
we're already making heavy use of the atomic_t API, which operates
exclusively on signed types.

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/20191121115902.2551-3-will@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 3 insertions, 3 deletions

diff --git a/lib/refcount.c b/lib/refcount.c
index 48b78a423d7d..719b0bc42ab1 100644
--- a/lib/refcount.c
+++ b/lib/refcount.c
@@ -61,7 +61,7 @@
  *
  * Return: false if the passed refcount is 0, true otherwise
  */
-bool refcount_add_not_zero_checked(unsigned int i, refcount_t *r)
+bool refcount_add_not_zero_checked(int i, refcount_t *r)
 {
 	unsigned int new, val = atomic_read(&r->refs);
 
@@ -101,7 +101,7 @@ 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(unsigned int i, refcount_t *r)
+void refcount_add_checked(int i, refcount_t *r)
 {
 	WARN_ONCE(!refcount_add_not_zero_checked(i, r), "refcount_t: addition on 0; use-after-free.\n");
 }
@@ -180,7 +180,7 @@ EXPORT_SYMBOL(refcount_inc_checked);
  *
  * Return: true if the resulting refcount is 0, false otherwise
  */
-bool refcount_sub_and_test_checked(unsigned int i, refcount_t *r)
+bool refcount_sub_and_test_checked(int i, refcount_t *r)
 {
 	unsigned int new, val = atomic_read(&r->refs);