From ccf3cd471eb7e215cd5d137f71a7fe0f87b20455 Mon Sep 17 00:00:00 2001
From: Michael Ellerman <mpe@ellerman.id.au>
Date: Fri, 14 Jul 2017 14:49:41 -0700
Subject: [PATCH] lib/atomic64_test.c: add a test that atomic64_inc_not_zero()
returns an int
atomic64_inc_not_zero() returns a "truth value" which in C is
traditionally an int. That means callers are likely to expect the
result will fit in an int.
If an implementation returns a "true" value which does not fit in an
int, then there's a possibility that callers will truncate it when they
store it in an int.
In fact this happened in practice, see commit 8fc39be920a9
("percpu-refcount: fix reference leak during percpu-atomic transition").
So add a test that the result fits in an int, even when the input
doesn't. This catches the case where an implementation just passes the
non-zero input value out as the result.
Link: http://lkml.kernel.org/r/1499775133-1231-1-git-send-email-mpe@ellerman.id.au
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Cc: Douglas Miller <dougmill@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
lib/atomic64_test.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/lib/atomic64_test.c b/lib/atomic64_test.c
index fd70c0e0e6731..62ab629f51ca2 100644
--- a/lib/atomic64_test.c
+++ b/lib/atomic64_test.c
@@ -153,8 +153,10 @@ static __init void test_atomic64(void)
long long v0 = 0xaaa31337c001d00dLL;
long long v1 = 0xdeadbeefdeafcafeLL;
long long v2 = 0xfaceabadf00df001LL;
+ long long v3 = 0x8000000000000000LL;
long long onestwos = 0x1111111122222222LL;
long long one = 1LL;
+ int r_int;
atomic64_t v = ATOMIC64_INIT(v0);
long long r = v0;
@@ -240,6 +242,11 @@ static __init void test_atomic64(void)
BUG_ON(!atomic64_inc_not_zero(&v));
r += one;
BUG_ON(v.counter != r);
+
+ /* Confirm the return value fits in an int, even if the value doesn't */
+ INIT(v3);
+ r_int = atomic64_inc_not_zero(&v);
+ BUG_ON(!r_int);
}
static __init int test_atomics_init(void)
--
2.39.5