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kern/46248: kevent won't return when kqueue is being closed

>Number:         46248
>Category:       kern
>Synopsis:       kevent won't return when kqueue is being closed
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Mar 23 01:10:01 +0000 2012
>Originator:     Julian Fagir
>Release:        6.0_BETA
NetBSD eselhitler 6.0_BETA NetBSD 6.0_BETA (ESELHITLER) #15: Fri Mar 16 
12:21:49 CET 2012  
gnrp@eselhitler:/home/ssd/netbsd-6.0/sys/arch/amd64/compile/obj/ESELHITLER amd64
NetBSD devrandom 6.0_BETA NetBSD 6.0_BETA (GENERIC) sparc64
Apparently, FreeBSD and NetBSD handle kqueue'ing differently when the kqueue 
underneath a kevent(2) call is closed.

On FreeBSD, closing the kqueue just succeeds and kevent returns, or whatever, 
at least the close(2) call succeeds.
On NetBSD, the close won't return. If you have a pending kevent without timeout 
(i.e. last field set to NULL), you won't be able to shut that call down (at 
least not by this way).
Save the attached program to `test.c`, and then compile and run with
`cc -lpthread test.c; time ./a.out`.
On NetBSD, this won't return until you stop it manually.
On FreeBSD, this will return after one second.

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/event.h>
#include <sys/time.h>
#include <pthread.h>

static void *
closekq(void *kq)
        close(*(int *) kq);

main(int argc, char *argv[])
        int kq, event;
        struct kevent kq_events;
        pthread_t thr;

        if ((kq = kqueue()) == -1)
                err(1, "kqueue");
        if (pthread_create(&thr, NULL, closekq, &kq))
                err(1, "pthread_create");
        event = kevent(kq, NULL, 0, &kq_events, 1, NULL);
        if (event == -1)
                err(1, "kevent");
        return 0;


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