ptrace bug in -rc2+

[Gerd Knorr <kraxel@bytesex.org>]

  Hi,

The introduction of the new TASK_TRACED state in 2.6.9-rc2 changed the
behavior of the kernel in a IMHO buggy way.  Sending a SIGKILL to a
process which is traced _and_ stopped doesn't work any more.  user mode
linux kernels do that on shutdown, thats why I ran into this.

Below is a short test app which shows the behavior.  On 2.6.9-rc2+ the
last waitpid() call blocks forever, on older kernels it doesn't ...

  Gerd

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#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
#include <sys/ptrace.h>
#include <sys/types.h>
#include <sys/wait.h>

int main(int argc, char *argv[])
{
	int child,rc,status;

	child = fork();
	if (0 == child) {
		fprintf(stderr,"[child] ptrace me ...\n");
		ptrace(PTRACE_TRACEME);
		fprintf(stderr,"[child] exec sleep 10 ...\n");
		execlp("sleep", "sleep", "10", NULL);
		perror("execlp");
		exit(1);
	}

	sleep(1);
	fprintf(stderr,"kill %d,STOP ...\n",child);
	kill(child,SIGSTOP);
	fprintf(stderr,"waitpid %d...\n",child);
	rc = waitpid(child,&status,WUNTRACED);
	fprintf(stderr,"%s: rc=%d status=%s%s%s termsig=%d\n",__FUNCTION__,rc,
		WIFEXITED(status)   ? "exit"    : "",
		WIFSIGNALED(status) ? "signal"  : "",
		WIFSTOPPED(status)  ? "stopped" : "",
		WTERMSIG(status));

	sleep(1);
	fprintf(stderr,"kill %d,KILL ...\n",child);
	kill(child,SIGKILL);
	fprintf(stderr,"waitpid %d...\n",child);
	rc = waitpid(child,&status,WUNTRACED);
	fprintf(stderr,"%s: rc=%d status=%s%s%s termsig=%d\n",__FUNCTION__,rc,
		WIFEXITED(status)   ? "exit"    : "",
		WIFSIGNALED(status) ? "signal"  : "",
		WIFSTOPPED(status)  ? "stopped" : "",
		WTERMSIG(status));

	exit(0);
}