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Date: Tue, 26 Sep 2023 15:02:08 -0400
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Justin Stitt <justinstitt@...gle.com>,
Peter Zijlstra <peterz@...radead.org>,
"Paul E. McKenney" <paulmck@...nel.org>,
Boqun Feng <boqun.feng@...il.com>,
Shuah Khan <shuah@...nel.org>,
Nathan Chancellor <nathan@...nel.org>,
Nick Desaulniers <ndesaulniers@...gle.com>,
Tom Rix <trix@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
llvm@...ts.linux.dev
Subject: Re: [PATCH] selftests/rseq: fix kselftest Clang build warnings
On 9/26/23 08:20, Justin Stitt wrote:
> Ping.
>
> Looking to get this patch and [1] slated for 6.7 which fixes some
> kselftest builds on older kernels.
>
> On Wed, Sep 13, 2023 at 6:03 AM Justin Stitt <justinstitt@...gle.com> wrote:
>>
>> When building with Clang, I am getting many warnings from the selftests/rseq tree.
>>
>> Here's one such example from rseq tree:
>> | param_test.c:1234:10: error: address argument to atomic operation must be a pointer to _Atomic type ('intptr_t *' (aka 'long *') invalid)
>> | 1234 | while (!atomic_load(&args->percpu_list_ptr)) {}
>> | | ^ ~~~~~~~~~~~~~~~~~~~~~~
>> | /usr/local/google/home/justinstitt/repos/tc-build/build/llvm/final/lib/clang/18/include/stdatomic.h:140:29: note: expanded from macro 'atomic_load'
>> | 140 | #define atomic_load(object) __c11_atomic_load(object, __ATOMIC_SEQ_CST)
>> | | ^ ~~~~~~
>>
>> Use compiler builtins `__atomic_load_n()` and `__atomic_store_n()` with
>> accompanying __ATOMIC_ACQUIRE and __ATOMIC_RELEASE, respectively. This
>> will fix the warnings because the compiler builtins do not expect their
>> arguments to have _Atomic type. This should also make TSAN happier.
>>
>> Link: https://github.com/ClangBuiltLinux/linux/issues/1698
>> Link: https://github.com/ClangBuiltLinux/continuous-integration2/issues/61
>> Suggested-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
>> Signed-off-by: Justin Stitt <justinstitt@...gle.com>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Peter, should this go through tip ?
Shuah, should to go through selftests ?
Thanks,
Mathieu
>> ---
>> Note: Previous RFC https://lore.kernel.org/r/20230908-kselftest-param_test-c-v1-1-e35bd9052d61@google.com
>> ---
>> tools/testing/selftests/rseq/param_test.c | 20 ++++++++++----------
>> 1 file changed, 10 insertions(+), 10 deletions(-)
>>
>> diff --git a/tools/testing/selftests/rseq/param_test.c b/tools/testing/selftests/rseq/param_test.c
>> index bf951a490bb4..20403d58345c 100644
>> --- a/tools/testing/selftests/rseq/param_test.c
>> +++ b/tools/testing/selftests/rseq/param_test.c
>> @@ -1231,7 +1231,7 @@ void *test_membarrier_worker_thread(void *arg)
>> }
>>
>> /* Wait for initialization. */
>> - while (!atomic_load(&args->percpu_list_ptr)) {}
>> + while (!__atomic_load_n(&args->percpu_list_ptr, __ATOMIC_ACQUIRE)) {}
>>
>> for (i = 0; i < iters; ++i) {
>> int ret;
>> @@ -1299,22 +1299,22 @@ void *test_membarrier_manager_thread(void *arg)
>> test_membarrier_init_percpu_list(&list_a);
>> test_membarrier_init_percpu_list(&list_b);
>>
>> - atomic_store(&args->percpu_list_ptr, (intptr_t)&list_a);
>> + __atomic_store_n(&args->percpu_list_ptr, (intptr_t)&list_a, __ATOMIC_RELEASE);
>>
>> - while (!atomic_load(&args->stop)) {
>> + while (!__atomic_load_n(&args->stop, __ATOMIC_ACQUIRE)) {
>> /* list_a is "active". */
>> cpu_a = rand() % CPU_SETSIZE;
>> /*
>> * As list_b is "inactive", we should never see changes
>> * to list_b.
>> */
>> - if (expect_b != atomic_load(&list_b.c[cpu_b].head->data)) {
>> + if (expect_b != __atomic_load_n(&list_b.c[cpu_b].head->data, __ATOMIC_ACQUIRE)) {
>> fprintf(stderr, "Membarrier test failed\n");
>> abort();
>> }
>>
>> /* Make list_b "active". */
>> - atomic_store(&args->percpu_list_ptr, (intptr_t)&list_b);
>> + __atomic_store_n(&args->percpu_list_ptr, (intptr_t)&list_b, __ATOMIC_RELEASE);
>> if (rseq_membarrier_expedited(cpu_a) &&
>> errno != ENXIO /* missing CPU */) {
>> perror("sys_membarrier");
>> @@ -1324,27 +1324,27 @@ void *test_membarrier_manager_thread(void *arg)
>> * Cpu A should now only modify list_b, so the values
>> * in list_a should be stable.
>> */
>> - expect_a = atomic_load(&list_a.c[cpu_a].head->data);
>> + expect_a = __atomic_load_n(&list_a.c[cpu_a].head->data, __ATOMIC_ACQUIRE);
>>
>> cpu_b = rand() % CPU_SETSIZE;
>> /*
>> * As list_a is "inactive", we should never see changes
>> * to list_a.
>> */
>> - if (expect_a != atomic_load(&list_a.c[cpu_a].head->data)) {
>> + if (expect_a != __atomic_load_n(&list_a.c[cpu_a].head->data, __ATOMIC_ACQUIRE)) {
>> fprintf(stderr, "Membarrier test failed\n");
>> abort();
>> }
>>
>> /* Make list_a "active". */
>> - atomic_store(&args->percpu_list_ptr, (intptr_t)&list_a);
>> + __atomic_store_n(&args->percpu_list_ptr, (intptr_t)&list_a, __ATOMIC_RELEASE);
>> if (rseq_membarrier_expedited(cpu_b) &&
>> errno != ENXIO /* missing CPU*/) {
>> perror("sys_membarrier");
>> abort();
>> }
>> /* Remember a value from list_b. */
>> - expect_b = atomic_load(&list_b.c[cpu_b].head->data);
>> + expect_b = __atomic_load_n(&list_b.c[cpu_b].head->data, __ATOMIC_ACQUIRE);
>> }
>>
>> test_membarrier_free_percpu_list(&list_a);
>> @@ -1401,7 +1401,7 @@ void test_membarrier(void)
>> }
>> }
>>
>> - atomic_store(&thread_args.stop, 1);
>> + __atomic_store_n(&thread_args.stop, 1, __ATOMIC_RELEASE);
>> ret = pthread_join(manager_thread, NULL);
>> if (ret) {
>> errno = ret;
>>
>> ---
>> base-commit: 2dde18cd1d8fac735875f2e4987f11817cc0bc2c
>> change-id: 20230908-kselftest-param_test-c-1763b62e762f
>>
>> Best regards,
>> --
>> Justin Stitt <justinstitt@...gle.com>
>>
>
> [1]: https://lore.kernel.org/all/20230908-kselftest-09-08-v2-0-0def978a4c1b@google.com/
>
> Thanks
> Justin
--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com
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