Commit ffba19cc authored by Michael Ellerman's avatar Michael Ellerman Committed by Linus Torvalds
Browse files

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 966d2b04
("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.


Signed-off-by: default avatarMichael Ellerman <>
Cc: Douglas Miller <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 37511fb5
......@@ -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)
r += one;
BUG_ON(v.counter != r);
/* Confirm the return value fits in an int, even if the value doesn't */
r_int = atomic64_inc_not_zero(&v);
static __init int test_atomics_init(void)
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