Bug 1662936

Created attachment 1517950 [details]
full strace log output on aarch64

Description of problem:
Latest strace-4.24-3.el8 occasionally reports '<ptrace(SYSCALL):No such process>' on getuid() calls when running the testcase below:

[root@qualcomm-amberwing-rep-10 ~]# cat many_looping_threads.c 
#include <stdio.h>
#include <pthread.h>
#include <unistd.h>
#include <sys/types.h>
#include <signal.h>
#include <stdlib.h>

static int thd_no;

static void *sub_thd(void *c)
{
	fprintf(stderr, "sub-thread %d created\n", ++thd_no);
	for (;;)
		getuid();
	return NULL;
}

int main(int argc, char *argv[])
{
	int i;
	pthread_t *thd;
	int num_threads = 1;

	if (argv[1])
		num_threads = atoi(argv[1]);

	thd = malloc(num_threads * sizeof(thd[0]));
	fprintf(stderr, "test start, num_threads:%d...\n", num_threads);
	for (i = 0; i < num_threads; i++) {
		pthread_create(&thd[i], NULL, sub_thd, NULL);
		fprintf(stderr, "after pthread_create\n");
	}
	/* Exit. This kills all threads */
	return 0;
}
[root@qualcomm-amberwing-rep-10 ~]# gcc many_looping_threads.c -o many_looping_threads -lpthread
[root@qualcomm-amberwing-rep-10 ~]# strace -f -o strace-log.log ./many_looping_threads 20
test start, num_threads:20...
after pthread_create
sub-thread 1 created
sub-thread 2 created
after pthread_create
after pthread_create
sub-thread 3 created
after pthread_create
sub-thread 4 created
after pthread_create
sub-thread 5 created
after pthread_create
sub-thread 6 created
after pthread_create
sub-thread 7 created
after pthread_create
sub-thread 8 created
after pthread_create
sub-thread 9 created
after pthread_create
sub-thread 10 created
after pthread_create
sub-thread 11 created
after pthread_create
sub-thread 12 created
after pthread_create
sub-thread 13 created
after pthread_create
sub-thread 14 created
after pthread_create
sub-thread 15 created
after pthread_create
sub-thread 16 created
after pthread_create
sub-thread 17 created
after pthread_create
sub-thread 18 created
after pthread_create
sub-thread 19 created
after pthread_create
sub-thread 20 created
[root@qualcomm-amberwing-rep-10 ~]# grep 'No such process' strace-log.log -C3
22468 getuid( <unfinished ...>
22467 exit_group(0 <unfinished ...>
22487 <... write resumed> )             = 22
22486 getuid( <ptrace(SYSCALL):No such process>
22485 <... getuid resumed> )            = ? <unavailable>
22484 ????( <unfinished ...>
22483 <... getuid resumed> )            = 0

The same tests also runs successfully sometimes, without any 'No such process' message.

Version-Release number of selected component (if applicable):
strace-4.24-3.el8
RHEL-8.0-20181220.1

How reproducible:
Occasionally