>Number:         7539
>Category:       kern
>Synopsis:       extent_alloc_subregion() doesn't
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    kern-bug-people (Kernel Bug People)
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sun May  9 08:35:00 1999
>Last-Modified:
>Originator:     Lennart Augustsson
>Organization:
>Release:        NetBSD-current 1999-05-09
>Environment:
System: NetBSD opus 1.4B NetBSD 1.4B (OPUS) #0: Sun May 9 16:53:38 CEST 1999 augustss@opus:/extra/NetBSD/src/sys/arch/i386/compile/OPUS i386


>Description:
	The extent_alloc_subregion() function is supposed to allocate
	an extent within the given substart-subend interval (if I
	understand right).  But sometimes it doesn't.  If the interval
	is above the last previous allocation it will allocate
	below substart.
>How-To-Repeat:
	Try it as described above.
>Fix:
	Well, just removing the code that moves the start location
	down seems to work for me.  But since this piece of code
	even has a comment describing what it does I don't dare make
	the change.  I simply don't understand why it was there in
	the first place, but it seems deliberate.
	I'll let the original author of the code figure it out.

	Furthermore, I've added a DIAGNOSTIC message if the allocation
	is outside the bounds.

*** subr_extent.c	Thu Feb 18 19:57:41 1999
--- /users/augustss/subr_extent.c	Sun May  9 17:22:00 1999
***************
*** 603,616 ****
  		last = rp;
  	}
  
- 	/*
- 	 * If there are no allocated regions beyond where we want to be,
- 	 * relocate the start of our candidate region to the end of
- 	 * the last allocated region (if there was one).
- 	 */
- 	if (rp == NULL && last != NULL)
- 		newstart = EXTENT_ALIGN((last->er_end + 1), alignment, skew);
- 
  	for (; rp != NULL; rp = rp->er_link.le_next) {
  		/*
  		 * Check the chunk before "rp".  Note that our
--- 603,608 ----
***************
*** 817,822 ****
--- 809,819 ----
  	return (EAGAIN);
  
   found:
+ #ifdef DIAGNOSTIC
+ 	if (newstart < substart || newstart + size > subend) {
+ 	    printf("extent_alloc_subregion: substart=%lx subend=%lx newstart=%lx\n", substart, subend, newstart);
+ 	}
+ #endif
  	/*
  	 * Insert ourselves into the region list.
  	 */
>Audit-Trail:
>Unformatted: