The patch titled
Subject: lib/atomic64_test.c: add a test that atomic64_inc_not_zero() returns an int
has been added to the -mm tree. Its filename is
lib-atomic64-test-add-a-test-that-atomic64_inc_not_zero-returns-an-int.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/lib-atomic64-test-add-a-test-that-atomic64_inc_not_zero-returns-an-int.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/lib-atomic64-test-add-a-test-that-atomic64_inc_not_zero-returns-an-int.patch
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From: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Subject: 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@xxxxxxxxxxxxxx
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: Douglas Miller <dougmill@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
lib/atomic64_test.c | 7 +++++++
1 file changed, 7 insertions(+)
diff -puN lib/atomic64_test.c~lib-atomic64-test-add-a-test-that-atomic64_inc_not_zero-returns-an-int lib/atomic64_test.c
--- a/lib/atomic64_test.c~lib-atomic64-test-add-a-test-that-atomic64_inc_not_zero-returns-an-int
+++ a/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)
_
Patches currently in -mm which might be from mpe@xxxxxxxxxxxxxx are
lib-atomic64-test-add-a-test-that-atomic64_inc_not_zero-returns-an-int.patch
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