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kern/39022: sysmon_envsys reports erroneous events

>Number:         39022
>Category:       kern
>Synopsis:       sysmon_envsys reports erroneous events
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sun Jun 22 16:35:00 +0000 2008
>Originator:     Paul Goyette
>Release:        NetBSD current 4.99.66
NetBSD 4.99.66 NetBSD 4.99.66 (QUICKY (ASUS M2N32 WS) 
2008-06-20 03:02:36) #1: Fri Jun 20 04:58:08 PDT 2008
In the case of a rapidly-changing sensor value, the current sysmon_envsys 
architecture will erroneously report multiple events for a single change in 
sensor value.  This is due to monitoring each individual threshold 

As an example, consider a sensor which has a crit_min value of 40 and a 
crit_max value of 50.

At T=0, the sensor is refreshed and the value is 45.  State is normal.

At T=1, the sensor is refreshed and the new value is 55.  This correctly 
triggers a USER_CRITOVER event.

Now, at T=2, the sensor is again refreshed and has a new value of 35.  The 
USER_CRITOVER event now erroneously reports a "back to normal" condition, AND 
the USER_CRITUNDER event reports its own event.

Unless you have a rapidly changing sensor, you can reproduce this bug manually 
by adjusting the user-specified crit_{min,max} values.  For example, if you 
have a temp sensor that stays between 34C and 38C, you can trigger the T=1 
event by setting crit_min = 20C and crit_max = 30C.  To trigger the T=2 event, 
just reset the limits to crit_min=40C and crit_max=50C.
I believe a fix for this requires modifications to the envsys2 design, to treat 
all the user-specified limits as a single monitor event, rather than as 
separate and independant events.

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