kern/147647: select wakes after 24 hours even if timeout is longer

[Martin Simmons]

>Number:         147647
>Category:       kern
>Synopsis:       select wakes after 24 hours even if timeout is longer
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Mon Jun 07 12:10:03 UTC 2010
>Closed-Date:
>Last-Modified:
>Originator:     Martin Simmons
>Release:        8.0-RELEASE-p2
>Organization:
>Environment:
FreeBSD lwfs1-cam.cam.lispworks.com 8.0-RELEASE-p2 FreeBSD 8.0-RELEASE-p2 #0: Tue Jan  5 21:11:58 UTC 2010     root at amd64-builder.daemonology.net:/usr/obj/usr/src/sys/GENERIC  amd64
>Description:
The select system call wakes indicating timeout after 24 hours even if the timeout specifies a longer delay.

>How-To-Repeat:
Running the code below with argument 10000000 exits after 24 hours with:
res = 0 delay = 86398 fd = 3, fd active = 0


#include <sys/select.h>
#include <unistd.h>
#include <time.h>
#include <stdio.h>
#include <stdlib.h>

int main(int argc, char **argv)
{
  fd_set fdset;
  struct timeval tv;
  int fds[2], fd, res;
  time_t start, end;

  pipe(fds);
  fd = fds[0];

  tv.tv_sec = atoi(argv[1]);
  tv.tv_usec = 0;
  FD_ZERO(&fdset);
  FD_SET(fd, &fdset);

  start = time(NULL);
  res = select(fd + 1, &fdset, NULL, NULL, &tv);
  end = time(NULL);

  printf("res = %d delay = %ld fd = %d, fd active = %d\n",
	 res, (long)(end - start), fd, FD_ISSET(fd, &fdset));

  return 0;
}


>Fix:
I think the problem is that seltdwait is implemented using cv_timedwait_sig, which returns EWOULDBLOCK on timeout.  The calls to seltdwait in kern_select etc limit the timeout to a maximum of 24 * 60 * 60 * hz but interpret EWOULDBLOCK as a reason to exit rather than checking the actual timeout.


>Release-Note:
>Audit-Trail:
>Unformatted: