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Date: Tue, 26 Sep 2023 16:20:52 +0900
From: Justin Stitt <justinstitt@...gle.com>
To: Mathieu Desnoyers <mathieu.desnoyers@...icios.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
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>
> ---
> 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
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