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Date: Tue, 3 Feb 1998 19:54:18 -0800 (PST)
From: Matt Dillon <dillon@best.net>
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Subject: kern/5641: running processes at the IDLE priority (idprio) can crash the kernel
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>Number:         5641
>Category:       kern
>Synopsis:       running processes at the IDLE priority (idprio) can crash the kernel
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    freebsd-bugs
>State:          open
>Quarter:
>Keywords:
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Tue Feb  3 20:00:01 PST 1998
>Last-Modified:
>Originator:     Matt Dillon
>Organization:
BEST Internet communications
>Release:        FreeBSD 2.2.5-STABLE i386
>Environment:

	FreeBSD 2.2.5-stable, recent CVS

>Description:

	running processes on the IDLE queue, via idprio, can crash the kernel.

>How-To-Repeat:

	Run a process with idprio that accesses the disk a lot.
	Run a cpu-bound process at normal priority

	Try to do other things... the kernel will crash because the process
	at idprio will be tsleep'ing in biowait or ufslk2 or some other 
	critical point and create a cascade lock chain failure.

>Fix:
	
	Turn the idprio off by default.  Hell, get rid of it entirely, it
	sucks. :-)  Or fix the sleep priority stuff to ensure that the
	process runs at a normal priority while in supervisor mode.

	NOTE:  My previous bug reports in regards to run queue corruption
	are almost certainly THIS bug.  The run queue is NOT corrupted.  I
	thought it was because the process holding the base lock in the
	cascade failure was in a 'R'un state yet not getting any cpu.

							-Matt

>Audit-Trail:
>Unformatted: