kern/159013: kldunload dtraceall crashing if userland dtrace provider is in use

[Alex Samorukov]

>Number:         159013
>Category:       kern
>Synopsis:       kldunload dtraceall crashing if userland dtrace provider is in use
>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:   Mon Jul 18 17:20:14 UTC 2011
>Closed-Date:
>Last-Modified:
>Originator:     Alex Samorukov
>Release:        FreeBSD-STABLE
>Organization:
netart
>Environment:
FreeBSD bsd.home 8.2-STABLE FreeBSD 8.2-STABLE #3: Fri Jul 15 21:22:54 UTC 2011     root at bsd.home:/usr/obj/usr/src/sys/DTRACE  amd64

>Description:
I found that kldunload dtracell causing kernel crash if userland providers are in use.
>How-To-Repeat:
1) Compile kernel with DTRACE support on -STABLE.
2) Run program acting as userland provider. I am using mod_php + apache for this, see ports/158983 for the source. 
3) Load module (kldload dtraceall)
4) start the web server to initialize the provider. 
5) Do kldunload dtraceall. System will panic. 

bsd# head -n 31 core.txt.0
bsd.home dumped core - see /var/crash/vmcore.0

Mon Jul 18 22:10:40 UTC 2011

FreeBSD bsd.home 8.2-STABLE FreeBSD 8.2-STABLE #3: Fri Jul 15 21:22:54 UTC 2011     root at bsd.home:/usr/obj/usr/src/sys/DTRACE  amd64

panic: double fault

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Unread portion of the kernel message buffer:

Fatal double fault
rip = 0xffffffff808f2cf8
rsp = 0xffffff8126aa8f60
rbp = 0xffffff8126aa90e0
cpuid = 0; apic id = 00
panic: double fault
cpuid = 0
KDB: stack backtrace:
#0 0xffffffff8062d78e at kdb_backtrace+0x5e
#1 0xffffffff805f8d17 at panic+0x187
#2 0xffffffff808f2494 at dblfault_handler+0xa4
#3 0xffffffff808daced at Xdblfault+0xad
Uptime: 2m18s

6) if i`m unloading httpd before kldunload everything is fine. 

I think this bug is not critical, but needs to be fixed. 

>Fix:


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