Date: Fri, 26 Jun 1998 17:35:15 -0700 (PDT) From: Matthew Dillon <dillon@backplane.com> To: FreeBSD-gnats-submit@FreeBSD.ORG Subject: kern/7085: Possible bug in checks for scheduler need_resched() call Message-ID: <199806270035.RAA10806@apollo.backplane.com>
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>Number: 7085
>Category: kern
>Synopsis: maybe_resched() priority check conditionals may be wrong.
>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: Fri Jun 26 17:40:01 PDT 1998
>Last-Modified:
>Originator: Matthew Dillon
>Organization:
Best Internet Communications, Inc.
>Release: FreeBSD 3.0-CURRENT i386
>Environment:
FreeBSD-current from CVS, PPro 200
>Description:
While searching for another bug, I found a bug in the priority
testing code in maybe_resched(). The bug is not critical, but
should probably be fixed.
The problem is that maybe_resched() is not properly handling the
case where a realtime process wakes up in the face of a normal
process running. It explicitly checks for the current process being
on the idle priority queue, but that isn't good enough. It also
improperly calls need_resched() when one idle-queue process wakes up
in the face of another running idle-queue process.
Properly it should check the case where p_priority is less then
curpriority, but ALSO check the case where the chk process's queue
number is less (more realtime) then the current processes queue.
Please check my work. This bug report is not in response to an
experienced problem, just something I saw as I was tracking down
another problem.
>How-To-Repeat:
>Fix:
Index: sys/kern/kern_synch.c
===================================================================
RCS file: /src/FreeBSD-CVS/ncvs/src/sys/kern/kern_synch.c,v
retrieving revision 1.57
diff -c -r1.57 kern_synch.c
*** kern_synch.c 1998/05/28 09:30:19 1.57
--- kern_synch.c 1998/06/27 00:29:28
***************
*** 112,121 ****
* the priority of the new one is higher then reschedule.
*/
if (p == 0 ||
! RTP_PRIO_BASE(p->p_rtprio.type) == RTP_PRIO_IDLE ||
(chk->p_priority < curpriority &&
! RTP_PRIO_BASE(p->p_rtprio.type) == RTP_PRIO_BASE(chk->p_rtprio.type)) )
need_resched();
}
#define ROUNDROBIN_INTERVAL (hz / quantum)
--- 112,124 ----
* the priority of the new one is higher then reschedule.
*/
if (p == 0 ||
! /* RTP_PRIO_BASE(p->p_rtprio.type) == RTP_PRIO_IDLE || */
(chk->p_priority < curpriority &&
! RTP_PRIO_BASE(p->p_rtprio.type) == RTP_PRIO_BASE(chk->p_rtprio.type)) ||
! RTP_PRIO_BASE(chk->p_rtprio.type) < RTP_PRIO_BASE(p->p_rtprio.type)
! ) {
need_resched();
+ }
}
#define ROUNDROBIN_INTERVAL (hz / quantum)
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