cygwin 3.6.0: Signals may fail permanently if received after SIGSTOP

Mon Feb 24 10:29:59 GMT 2025

Found with 'stress-ng --cpu-sched 1':
Testcase (attached):
$ uname -r
3.6.0-0.387.g8cebbb2b42bf.x86_64
$ gcc -o timersig timersig.c
$ ./timersig
638: fork()=639
!!!!!!!!!!!!!...!!!!!!!!!!!!!SIGSTOP: Permission denied
     0 [itimer] timersig 639 sig_send: error sending signal 14, pid 639, 
pipe handle 0x14C, nb 0, packsize 192, Win32 error 0
SIGKILL: Permission denied
$ kill 639
-bash: kill: (639) - Permission denied
$ kill -9 639
-bash: kill: (639) - Permission denied
$ /bin/kill --force 639
$ /bin/kill --force 639
kill: 639: No such process
A similar problem, but without the "error sending signal" message, 
occurs if the timer is not used but the parent process issues SIGSTOP 
SIGALRM SIGCONT ... sequences.
-- 
Regards,
Christian
-------------- next part --------------
#include <sched.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <unistd.h>
#include <sys/wait.h>
static sig_atomic_t sigcnt;
static void sighandler(int sig)
{
 (void)sig;
 ++sigcnt;
 write(1, "!", 1);
}
int main()
{
 pid_t pid = fork();
 if (pid == (pid_t)-1) {
 perror("fork"); return 1;
 }
 if (!pid) {
 signal(SIGALRM, sighandler);
 timer_t tid;
 if (timer_create(CLOCK_REALTIME, NULL, &tid)) {
 perror("timer_create"); _exit(1);
 }
 struct itimerspec t = {};
 t.it_value.tv_nsec = t.it_interval.tv_nsec = 100;
 timer_settime(tid, 0, &t, NULL); 
 while (sigcnt < 1000)
 sched_yield();
 printf("%d: exit\n", (int)getpid()); fflush(stdout);
 _exit(0);
 }
 printf("%d: fork()=%d\n", (int)getpid(), (int)pid);
 sleep(1);
 int wp, status;
 while (!(wp = waitpid(pid, &status, WNOHANG))) {
 sched_yield();
 if (kill(pid, SIGSTOP)) {
 perror("SIGSTOP"); break;
 }
 sched_yield();
 if (kill(pid, SIGCONT)) {
 perror("SIGCONT"); break;
 }
 }
 if (wp < 0)
 perror("waitpid");
 else if (!wp && kill(pid, SIGKILL))
 perror("SIGKILL");
 return (wp <= 0);
}