linux-kernel - Re: [RFC][PATCH 00/12] Introduce cmpxchg128() -- aka. the demise of cmpxchg

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Message-ID: <Y6OxBW5F/ZF5wocE@boqun-archlinux>
Date:   Wed, 21 Dec 2022 17:21:09 -0800
From:   Boqun Feng <boqun.feng@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     torvalds@...ux-foundation.org, corbet@....net, will@...nel.org,
        mark.rutland@....com, catalin.marinas@....com, dennis@...nel.org,
        tj@...nel.org, cl@...ux.com, hca@...ux.ibm.com, gor@...ux.ibm.com,
        agordeev@...ux.ibm.com, borntraeger@...ux.ibm.com,
        svens@...ux.ibm.com, Herbert Xu <herbert@...dor.apana.org.au>,
        davem@...emloft.net, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, dave.hansen@...ux.intel.com, x86@...nel.org,
        hpa@...or.com, joro@...tes.org, suravee.suthikulpanit@....com,
        robin.murphy@....com, dwmw2@...radead.org,
        baolu.lu@...ux.intel.com, Arnd Bergmann <arnd@...db.de>,
        penberg@...nel.org, rientjes@...gle.com, iamjoonsoo.kim@....com,
        Andrew Morton <akpm@...ux-foundation.org>, vbabka@...e.cz,
        roman.gushchin@...ux.dev, 42.hyeyoo@...il.com,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-s390@...r.kernel.org,
        linux-crypto@...r.kernel.org, iommu@...ts.linux.dev,
        linux-arch@...r.kernel.org
Subject: Re: [RFC][PATCH 00/12] Introduce cmpxchg128() -- aka. the demise of
 cmpxchg_double()

Hi Peter,

On Mon, Dec 19, 2022 at 04:35:25PM +0100, Peter Zijlstra wrote:
> Hi,
> 
> Since Linus hated on cmpxchg_double(), a few patches to get rid of it, as proposed here:
> 
>   https://lkml.kernel.org/r/Y2U3WdU61FvYlpUh@hirez.programming.kicks-ass.net
> 
> based on tip/master because Linus' tree is moving a wee bit fast at the moment.
> 
> 0day robot is all green for building, very limited testing on arm64/s390
> for obvious raisins -- I tried to get the asm right, but please, double
> check.
> 

I added some test cases for cmpxcgh128 APIs, and found two issues. I
will reply separately in the patches. The test cases themselves are at
the end, let me know if you want to me to send a proper patch.

Regards,
Boqun

------------------------------------------------------------>8
Subject: [PATCH] atomic: Add test cases for cmpxchg128 family

Besides for 32bit and 64bit cmpxchg, we only test via atomic_cmpxchg_*
APIs, add tests via cmpxchg* APIs while we are at it.

Signed-off-by: Boqun Feng <boqun.feng@...il.com>
---
 lib/atomic64_test.c | 41 ++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 40 insertions(+), 1 deletion(-)

diff --git a/lib/atomic64_test.c b/lib/atomic64_test.c
index d9d170238165..7f79d0704ba8 100644
--- a/lib/atomic64_test.c
+++ b/lib/atomic64_test.c
@@ -76,12 +76,19 @@ do {								\
 	BUG_ON(atomic##bit##_read(&v) != expect);		\
 } while (0)
 
+#define TEST_ARGS_PLAIN(_, op, init, ret, expect, args...)	\
+do {								\
+	__WRITE_ONCE(n, init);					\
+	BUG_ON(op(&n, ##args) != ret);				\
+	BUG_ON(__READ_ONCE(n) != expect);			\
+} while (0)
+
 #define XCHG_FAMILY_TEST(bit, init, new)				\
 do {									\
 	FAMILY_TEST(TEST_ARGS, bit, xchg, init, init, new, new);	\
 } while (0)
 
-#define CMPXCHG_FAMILY_TEST(bit, init, new, wrong)			\
+#define ATOMIC_CMPXCHG_FAMILY_TEST(bit, init, new, wrong)		\
 do {									\
 	FAMILY_TEST(TEST_ARGS, bit, cmpxchg, 				\
 			init, init, new, init, new);			\
@@ -89,6 +96,14 @@ do {									\
 			init, init, init, wrong, new);			\
 } while (0)
 
+#define CMPXCHG_FAMILY_TEST(bit, init, new, wrong)			\
+do {									\
+	FAMILY_TEST(TEST_ARGS_PLAIN, _, cmpxchg##bit, 			\
+			init, init, new, init, new);			\
+	FAMILY_TEST(TEST_ARGS_PLAIN, _, cmpxchg##bit,			\
+			init, init, init, wrong, new);			\
+} while (0)
+
 #define INC_RETURN_FAMILY_TEST(bit, i)			\
 do {							\
 	FAMILY_TEST(TEST_ARGS, bit, inc_return,		\
@@ -109,6 +124,7 @@ static __init void test_atomic(void)
 	int one = 1;
 
 	atomic_t v;
+	int n;
 	int r;
 
 	TEST(, add, +=, onestwos);
@@ -139,6 +155,7 @@ static __init void test_atomic(void)
 	DEC_RETURN_FAMILY_TEST(, v0);
 
 	XCHG_FAMILY_TEST(, v0, v1);
+	ATOMIC_CMPXCHG_FAMILY_TEST(, v0, v1, onestwos);
 	CMPXCHG_FAMILY_TEST(, v0, v1, onestwos);
 
 }
@@ -155,6 +172,7 @@ static __init void test_atomic64(void)
 	int r_int;
 
 	atomic64_t v = ATOMIC64_INIT(v0);
+	long long n = 0;
 	long long r = v0;
 	BUG_ON(v.counter != r);
 
@@ -201,6 +219,7 @@ static __init void test_atomic64(void)
 	DEC_RETURN_FAMILY_TEST(64, v0);
 
 	XCHG_FAMILY_TEST(64, v0, v1);
+	ATOMIC_CMPXCHG_FAMILY_TEST(64, v0, v1, v2);
 	CMPXCHG_FAMILY_TEST(64, v0, v1, v2);
 
 	INIT(v0);
@@ -245,10 +264,30 @@ static __init void test_atomic64(void)
 	BUG_ON(!r_int);
 }
 
+#ifdef system_has_cmpxchg128
+static __init void test_atomic128(void)
+{
+	long long v0 = 0xaaa31337c001d00dLL;
+	long long v1 = 0xdeadbeefdeafcafeLL;
+	long long v2 = 0xfaceabadf00df001LL;
+	long long v3 = 0x8000000000000000LL;
+
+	s128 init = ((s128)v0 << 64) + v1;
+	s128 new = ((s128)v1 << 64) + v0;
+	s128 wrong = ((s128)v2 << 64) + v3;
+	s128 n = 1;
+
+	CMPXCHG_FAMILY_TEST(128, init, new, wrong);
+}
+#else
+static __init void test_atomic128(void) {}
+#endif
+
 static __init int test_atomics_init(void)
 {
 	test_atomic();
 	test_atomic64();
+	test_atomic128();
 
 #ifdef CONFIG_X86
 	pr_info("passed for %s platform %s CX8 and %s SSE\n",
-- 
2.38.1