From owner-freebsd-current  Sun Jul 21 16:52: 4 2002
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Date: Sun, 21 Jul 2002 16:43:47 -0700 (PDT)
From: David Xu <bsddiy@yahoo.com>
Subject: signal handling bug in KSE MIII
To: Julian Elischer <julian@elischer.org>
Cc: freebsd-current@freebsd.org
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I found signal handling is still broken in CURRENT source.
the following program demostrates the bug is still in kernel:

#include <stdio.h>
#include <signal.h>

void handler(int sig)
{
     signal(SIGTSTP, SIG_DFL);
     kill(getpid(), SIGTSTP);
}

int main()
{
    char buf[64];

    signal(SIGTSTP, handler);
    kill(getpid(), SIGTSTP);
    printf("input foo:");
    scanf("%63s", buf);
    printf("you input:%s\n", buf);
    return 0;
}

when I press CTRL+Z, the program does not suspend and directly exits.
ktrace indicates that the program directly exits in kernel without 
calling exit() from program.
I found SA_STOP handling is disabled in issignal(), delayed SIGTSTP
is forgotten by kernel, this is the reason why SIGTSTP signal handling
is broken. at least, one program is affected --- ftp, run ftp
client program, when 'ftp>' prompt appears, pressing CTRL+Z, causes ftp 
to exit and do not suspend. patch:

--- kern_sig.c.old	Sun Jul 21 15:38:00 2002
+++ kern_sig.c	Sun Jul 21 16:31:02 2002
@@ -1657,7 +1657,7 @@
 #endif
 				break;		/* == ignore */
 			}
-#if 0
+
 			/*
 			 * If there is a pending stop signal to process
 			 * with default action, stop here,
@@ -1679,16 +1679,10 @@
 				PROC_UNLOCK(p->p_pptr);
 				mtx_lock_spin(&sched_lock);
 				stop(p);
-				PROC_UNLOCK(p);
-				DROP_GIANT();
-				p->p_stats->p_ru.ru_nivcsw++;
-				mi_switch();
 				mtx_unlock_spin(&sched_lock);
-				PICKUP_GIANT();
-				PROC_LOCK(p);
 				break;
 			} else
-#endif
+
 			     if (prop & SA_IGNORE) {
 				/*
 				 * Except for SIGCONT, shouldn't get here.

David Xu


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