[155] in Pthreads Bugs

pthread_kill() Bug

daemon@ATHENA.MIT.EDU (Thu Dec 26 20:34:45 1996 )

From: Chris Colohan <colohan@eecg.toronto.edu>
To: pthreads-bugs@MIT.EDU, proven@MIT.EDU
Date: 	Thu, 26 Dec 1996 20:33:48 -0500

pthread_kill() has a problem in PThreads 1.60beta6.  It checks to see
if the target thread is in the state PS_SIGWAIT, and if it is it
reschedules it.  But it does not check if there is more than one
thread in the PS_SIGWAIT state, and hence mangles the pthread_sigwait
linked list, potentially resulting in threads getting blocked forever,
and signals never being delivered.  I have a *very* contrived test
case that demonstrates this problem if you would like it.  Please let
me know...

Chris
===

Diffs created with diff -c:

*** /home/colohan/thesis/t/pthreads-1_60_beta6/pthreads/pthread_kill.c	Tue Feb 21 03:07:18 1995
--- pthread_kill.c	Thu Dec 26 19:50:22 1996
***************
*** 41,51 ****
--- 41,58 ----
  
  #include <pthread.h>
  
+ /* Defined in sig.c, a linked list of threads currently
+  * blocked in sigwait(): */
+ extern struct pthread * pthread_sigwait;
+ 
+ 
  /* ==========================================================================
   * pthread_kill()
   */
  int pthread_kill(struct pthread * pthread, int sig)
  {
+ 	struct pthread ** pthread_ptr;
+ 
  	pthread_sched_prevent();
  
  	/* Check who is the current owner of pthread */
***************
*** 53,62 ****
  	if (0) {
  	} else {
  		if (pthread->state == PS_SIGWAIT) {
! 			if (sigismember(pthread->data.sigwait, sig)) {
! 				*(int *)(pthread->ret) = sig;
! 				pthread_sched_other_resume(pthread);
! 				return(OK);
  			}
  		}
  		sigaddset(&(pthread->sigpending), sig);
--- 60,84 ----
  	if (0) {
  	} else {
  		if (pthread->state == PS_SIGWAIT) {
! 			if(sigismember(pthread->data.sigwait, sig)) {
! 			    for (pthread_ptr = &pthread_sigwait;
! 				 (*pthread_ptr);
! 				 pthread_ptr = &((*pthread_ptr)->next)) {
! 				if ((*pthread_ptr) == pthread) {
! 
! 				    /* Take the thread out of the
! 				     * pthread_sigwait linked list: */
! 				    *pthread_ptr=(*pthread_ptr)->next;
! 			
! 				    *(int *)(pthread->ret) = sig;
! 				    pthread_sched_other_resume(pthread);
! 				    return(OK);
! 				}
! 			    }
! 			    /* A thread should not be in the state PS_SIGWAIT
! 			     * without being in the pthread_sigwait linked
! 			     * list: */
! 			    PANIC();
  			}
  		}
  		sigaddset(&(pthread->sigpending), sig);