From: Martin KaFai Lau <martin.lau@linux.dev>
To: Amery Hung <ameryhung@gmail.com>
Cc: daniel@iogearbox.net, andrii@kernel.org,
alexei.starovoitov@gmail.com, martin.lau@kernel.org,
kernel-team@meta.com, bpf@vger.kernel.org
Subject: Re: [PATCH bpf-next v4 3/3] selftests/bpf: Fix dangling stdout seen by traffic monitor thread
Date: Tue, 4 Mar 2025 17:36:14 -0800 [thread overview]
Message-ID: <716c1a2d-f4fb-407f-b77d-03019e0dd2a5@linux.dev> (raw)
In-Reply-To: <20250304163626.1362031-3-ameryhung@gmail.com>
On 3/4/25 8:36 AM, Amery Hung wrote:
> diff --git a/tools/testing/selftests/bpf/test_progs.c b/tools/testing/selftests/bpf/test_progs.c
> index ab0f2fed3c58..5b89f6ca5a0a 100644
> --- a/tools/testing/selftests/bpf/test_progs.c
> +++ b/tools/testing/selftests/bpf/test_progs.c
> @@ -88,7 +88,11 @@ static void stdio_hijack(char **log_buf, size_t *log_cnt)
> #endif
> }
>
> -static void stdio_restore_cleanup(void)
> +static pthread_mutex_t stdout_lock = PTHREAD_MUTEX_INITIALIZER;
> +
> +static bool in_crash_handler(void);
> +
> +static void stdio_restore(void)
> {
> #ifdef __GLIBC__
> if (verbose() && env.worker_id == -1) {
> @@ -98,34 +102,34 @@ static void stdio_restore_cleanup(void)
>
> fflush(stdout);
>
> - if (env.subtest_state) {
> + pthread_mutex_lock(&stdout_lock);
> +
> + if (!env.subtest_state || in_crash_handler()) {
Can the stdio restore be done in the crash_handler() itself instead of having a
special case here and adding another in_crash_handler()?
Theoretically, the crash_handler() only needs to
fflush(stdout /* whatever the current stdout is */) and...
> + if (stdout == env.stdout_saved)
> + goto out;
> +
> + fclose(env.test_state->stdout_saved);
> + env.test_state->stdout_saved = NULL;
> + stdout = env.stdout_saved;
> + stderr = env.stderr_saved;
... restore std{out,err} = env.std{out,err}_saved.
At the crash point, it does not make a big difference to
fclose(evn.test_state->stdout_saved) or not?
If the crash_handler() does not close the stdout that the traffic monitor might
potentially be using, then crash_handler() does not need to take mutex, right?
> + } else {
> fclose(env.subtest_state->stdout_saved);
> env.subtest_state->stdout_saved = NULL;
> stdout = env.test_state->stdout_saved;
> stderr = env.test_state->stdout_saved;
> - } else {
> - fclose(env.test_state->stdout_saved);
> - env.test_state->stdout_saved = NULL;
> }
> +out:
> + pthread_mutex_unlock(&stdout_lock);
> #endif
> }
>
[ ... ]
> +static bool in_crash_handler(void)
> +{
> + struct sigaction sigact;
> +
> + /* sa_handler will be cleared if invoked since crash_handler is
> + * registered with SA_RESETHAND
> + */
> + sigaction(SIGSEGV, NULL, &sigact);
> +
> + return sigact.sa_handler != crash_handler;
> +}
> +
next prev parent reply other threads:[~2025-03-05 1:36 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-03-04 16:36 [PATCH bpf-next v4 1/3] selftests/bpf: Clean up call sites of stdio_restore() Amery Hung
2025-03-04 16:36 ` [PATCH bpf-next v4 2/3] selftests/bpf: Allow assigning traffic monitor print function Amery Hung
2025-03-04 16:36 ` [PATCH bpf-next v4 3/3] selftests/bpf: Fix dangling stdout seen by traffic monitor thread Amery Hung
2025-03-05 0:12 ` Eduard Zingerman
2025-03-05 16:52 ` Amery Hung
2025-03-05 1:36 ` Martin KaFai Lau [this message]
2025-03-05 16:52 ` Amery Hung
2025-03-04 21:48 ` [PATCH bpf-next v4 1/3] selftests/bpf: Clean up call sites of stdio_restore() Eduard Zingerman
2025-03-04 23:39 ` Amery Hung
2025-03-05 0:14 ` Eduard Zingerman
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