From ffba19ccae8d98beb0a17345a0b1ee9e415b23b8 Mon Sep 17 00:00:00 2001 From: Michael Ellerman 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 966d2b04e070 ("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 Cc: Douglas Miller Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- lib/atomic64_test.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/lib/atomic64_test.c b/lib/atomic64_test.c index fd70c0e0e673..62ab629f51ca 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