fix for thread signal delivery
PATCH 1/1 fix for thread signal delivery
A signal delivery to a thread is not working properly in the kernel when a signal handler is specified. Here is the case:
A process blocks all signals and registers a handler for a signal.
A newly created thread unblocks that signal. When that signal is sent to a process, the sighandler is not getting called.
(if this signal is sent twice, it works)
I've attached a small test program to reproduce it using NPTL.
The following patch fixes this problem in kernel. Please apply.
Thanks,
Saurabh Desai
kernel/signal.c +4 -2
@@ -854,11 +854,13 @@ tmp = p->sig->curr_target; -if (!tmp || tmp->tgid != p->tgid) +if (!tmp || tmp->tgid != p->tgid) {/* restart balancing at this thread */ p->sig->curr_target = p; + tmp = p; + } -else for (;;) { +for (;;) {if (thread_group_empty (p))BUG ();if (!tmp || tmp->tgid != p->tgid)
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <pthread.h>
#include <signal.h>
void sigcatcher(int sig)
{
fprintf(stderr, "The sigcatcher caught signal %d\n", sig);
pthread_exit(0);
}void *sig_thread(void *p)
{
sigset_t sigs_to_catch;
/* Unblock SIGINT */
sigemptyset(&sigs_to_catch);
sigaddset(&sigs_to_catch, SIGINT);
pthread_sigmask(SIG_UNBLOCK, &sigs_to_catch, NULL);
fprintf(stderr, "sent a SIGINT (ctrl-C) to this process(%d)\n", getpid());
sleep(60);
return (NULL);
}extern int main(void)
{
pthread_t thread;
sigset_t sigs_to_block;
struct sigaction action;
/* Block all signals */
sigfillset(&sigs_to_block);
pthread_sigmask(SIG_BLOCK, &sigs_to_block, NULL);
/* Set a signal handler */
action.sa_handler = sigcatcher;
action.sa_flags = 0;
sigaction(SIGINT, &action, NULL);
pthread_create(&thread, NULL, sig_thread, NULL);
/* wait until thread is finished */
pthread_join(thread, NULL);
return 0;
}