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selftests/bpf: Fix dangling stdout seen by traffic monitor thread

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Traffic monitor thread may see dangling stdout as the main thread closes
and reassigns stdout without protection. This happens when the main thread
finishes one subtest and moves to another one in the same netns_new()
scope.

The issue can be reproduced by running test_progs repeatedly with traffic
monitor enabled:

for ((i=1;i<=100;i++)); do
   ./test_progs -a flow_dissector_skb* -m '*'
done

For restoring stdout in crash_handler(), since it does not really care
about closing stdout, simlpy flush stdout and restore it to the original
one.

Then, Fix the issue by consolidating stdio_restore_cleanup() and
stdio_restore(), and protecting the use/close/assignment of stdout with
a lock. The locking in the main thread is always performed regradless of
whether traffic monitor is running or not for simplicity. It won't have
any side-effect.

Signed-off-by: Amery Hung <ameryhung@gmail.com>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://patch.msgid.link/20250305182057.2802606-3-ameryhung@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Amery Hung 2025-03-05 10:20:57 -08:00 committed by Alexei Starovoitov
parent 34a25aabcd
commit 8bda5b787d
1 changed files with 33 additions and 28 deletions
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61
tools/testing/selftests/bpf/test_progs.c
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@ -88,27 +88,7 @@ static void stdio_hijack(char **log_buf, size_t *log_cnt)
#endif
}
static void stdio_restore_cleanup(void)
{
#ifdef __GLIBC__
if (verbose() && env.worker_id == -1) {
/* nothing to do, output to stdout by default */
return;
}
fflush(stdout);
if (env.subtest_state) {
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;
}
#endif
}
static pthread_mutex_t stdout_lock = PTHREAD_MUTEX_INITIALIZER;
static void stdio_restore(void)
{
@ -118,16 +98,35 @@ static void stdio_restore(void)
return;
}
if (stdout == env.stdout_saved)
return;
fflush(stdout);
stdio_restore_cleanup();
pthread_mutex_lock(&stdout_lock);
stdout = env.stdout_saved;
stderr = env.stderr_saved;
if (env.subtest_state) {
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;
stdout = env.stdout_saved;
stderr = env.stderr_saved;
}
pthread_mutex_unlock(&stdout_lock);
#endif
}
static int traffic_monitor_print_fn(const char *format, va_list args)
{
pthread_mutex_lock(&stdout_lock);
vfprintf(stdout, format, args);
pthread_mutex_unlock(&stdout_lock);
return 0;
}
/* Adapted from perf/util/string.c */
static bool glob_match(const char *str, const char *pat)
{
@ -536,7 +535,8 @@ void test__end_subtest(void)
test_result(subtest_state->error_cnt,
subtest_state->skipped));
stdio_restore_cleanup();
stdio_restore();
env.subtest_state = NULL;
}
@ -1265,7 +1265,10 @@ void crash_handler(int signum)
sz = backtrace(bt, ARRAY_SIZE(bt));
stdio_restore();
fflush(stdout);
stdout = env.stdout_saved;
stderr = env.stderr_saved;
if (env.test) {
env.test_state->error_cnt++;
dump_test_log(env.test, env.test_state, true, false, NULL);
@ -1957,6 +1960,8 @@ int main(int argc, char **argv)
libbpf_set_strict_mode(LIBBPF_STRICT_ALL);
libbpf_set_print(libbpf_print_fn);
traffic_monitor_set_print(traffic_monitor_print_fn);
srand(time(NULL));
env.jit_enabled = is_jit_enabled();