ia64/147501: [ia64] options PREEMPTION causes instability

[Marcel Moolenaar]

>Number:         147501
>Category:       ia64
>Synopsis:       [ia64] options PREEMPTION causes instability
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    freebsd-ia64
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Sat Jun 05 17:00:16 UTC 2010
>Closed-Date:
>Last-Modified:
>Originator:     Marcel Moolenaar
>Release:        9-CURRENT
>Organization:
>Environment:
FreeBSD hob.lan.xcllnt.net 9.0-CURRENT FreeBSD 9.0-CURRENT #1 r208634:208809M: Sat Jun  5 08:36:47 PDT 2010     marcel at hob.lan.xcllnt.net:/usr/obj/nfs/freebsd/base/head/sys/HOB  ia64

>Description:
Running pho's stress2 with PREEMPTION results in kernel panics that are not seen when PREEMPTION is not enabled. This is with a SMP kernel.
>How-To-Repeat:
On a Montecito box:
o   checkout projects/stress2
o   compile and run
o   Wait for a panic (possibly a hard hang) within a few hours.

NOTE: Due to another bug, Montecito is the more reliable test platform.

>Fix:
Problem areas that are at the top of my head:
o   The weak memory ordering could result in race conditions if memory fences aren't properly used
o   Access to PCPU fields is non-atomic, which may result in getting the wrong field when the thread migrates to another CPU in the middle of the access sequence.


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