PROBLEM : Thread signal informations are not freed when it is execing.

* PROBLEM : Thread signal informations are not freed when it is execing.
@ 2004-10-21 13:02 Laurent Dufour
  2004-10-22  9:17 ` Roland McGrath
  0 siblings, 1 reply; 4+ messages in thread
From: Laurent Dufour @ 2004-10-21 13:02 UTC (permalink / raw)
  To: linux-kernel

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Hi,

It seems that under specific circumstances...

[1] Thread signal informations are not freed when it is execing.

[2] If a thread calling exec has pending signals with signal
informations then this signal informations are unlinked but not freed. 

It is easy to detect it with previous kernel 2.4.x because of rtsig-nr
sysctl value (see [6]).

On kernel 2.4 the result is that no RT signal information can be sent
when rtsig-nr reach is max value. On 2.6 kernels it can't be seen but
allocated memory is never freed.

Problem seems to be due to the call at init_sigpending at the end of
de_thread because it reset signal list without freeing linked items.
Perhaps it should be better to use flush_sigqueue.

In 2.6 kernel by reading de_thread function, it seems that problem still
exists.

[3] de_thread, pending signals, exec

[4] 2.4.21 but it seems also applicable to 2.6.8.1

[5] NA

[6] This small test cannot be run on 2.6 kernel because
"kernel.rtsig-nr" sysctl value doesn't exist anymore. But memory leak
seems to be still present in 2.6.8.1 kernel.

/*
 * This small program generate a memory leak of signal info structure.
 * It can't not be run on new kernel (2.6.x) because rtsig-nr doesn't
 * exist anymore but it seems that leak is still present in 2.6 kernels.
 *
 * The first time the test program is executed, it will set rtsig-nr to
 * it maximum (1024 is the default for kernel.rtsig-max).
 * Then no process can sent signal with information associated.
 * You can verify this by running test program again, it will say that
 * no signal can be sent (pthread_kill will return EAGAIN error).
 *
 * WARNING : You have to reboot the node to reset rtsig-nr value.
 *
 * Laurent Dufour <ldufour@meiosys.com>
 */

#define _GNU_SOURCE
#include <pthread.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <signal.h>

#define SIGNAL	SIGRTMAX

void *thread_fn(void * unused)
{
    sigset_t sset;
    int i;
    pthread_t me = pthread_self();

    /* printf("thread %p started\n", pthread_self()); */

    sigemptyset(&sset);
    sigaddset(&sset, SIGNAL);
    if (pthread_sigmask(SIG_BLOCK, &sset, NULL)) {
	perror("pthread_sigmask");
	exit(1);
    }

    i=0;
    while(1) {
	int err = pthread_kill(me, SIGNAL);
	if (err) {
	    if (!i) {
		printf("no signal sent, pthread_kill : %s\n",
		       strerror(err));
		exit(1);
	    }
	    break;
	}
	i++;
    }
    /* printf("%d signal sent.\n", i);*/

    printf("After thread is execing :");
    execlp("sysctl", "sysctl", "kernel.rtsig-nr", NULL);

    perror("execlp");

    exit(1);
}

void sig_handler(int signal, siginfo_t *info, void * unused)
{
    /* It should never be called since signal is blocked. */
    printf("thread %p catch signal %s\n",
	   pthread_self(), strsignal(signal));
}

int main(int argc, char **argv)
{
    pthread_t thread;
    struct sigaction act;

    setbuf(stdout,NULL);

    printf("Before thread's execing : ");
    system("sysctl kernel.rtsig-nr");

    act.sa_sigaction = sig_handler;
    sigemptyset(&act.sa_mask);
    act.sa_flags = SA_RESTART | SA_NOMASK | SA_SIGINFO;
    if (sigaction(SIGNAL, &act, NULL)) {
	perror("sigaction");
	exit(1);
    }

    if (pthread_create(&thread, NULL, thread_fn, NULL)) {
	perror("pthread_create");
	exit(1);
    }

    /* printf("wait for thread call exec...\n"); */
    while(1) pause();
}

[7] environnement doesn't seems to have any impact.

[8] Hope that helps.

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