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Date: Wed, 27 Jun 2001 14:15:14 -0700 (PDT)
From: Umesh Krishnaswamy <umesh@juniper.net>
To: freebsd-gnats-submit@FreeBSD.org
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Subject: kern/28465: Enabling softupdates on a clean but active filesystem can panic the kernel
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>Number:         28465
>Category:       kern
>Synopsis:       Enabling softupdates on a clean but active filesystem can panic 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:   Wed Jun 27 14:20:01 PDT 2001
>Closed-Date:
>Last-Modified:
>Originator:     Umesh Krishnaswamy
>Release:        4.2-STABLE
>Organization:
Juniper Networks
>Environment:
>Description:
If you do a bunch of reads and writes to a filesystem, then mount it
rdonly and enable softupdates, tunefs will allow you to do so, but 
the kernel will panic shortly afterwords with the following stack trace.

# tunefs -n enable /altroot
tunefs: soft updates setp
anic: softdep_deallocate_dependencies: dangling deps
softdep_deallocate_dependencies(c0368000,dcde5c98,c01b417a,d01cd00c,d01cd00c) at softdep_deallocate_dependencies+0x16
softdep_deallocate_dependencies(d01cd00c) at softdep_deallocate_dependencies+0x16
brelse(d01cd00c,d01cd00c) at brelse+0x6a
vinvalbuf(dcd2ee40,0,c41c9800,dcd92400,0) at vinvalbuf+0x24f
ffs_reload(c3b4be00,c41c9800,dcd92400,0,c3b4be00) at ffs_reload+0x51
ffs_mount(c3b4be00,4810890f,bfbff83c,dcde5e80,dcd92400) at ffs_mount+0x163
mount(dcd92400,dcde5f80,bfbff83c,bfbffdf9,8049517) at mount+0x4ef
syscall2(2f,2f,2f,8049517,bfbffdf9) at syscall2+0x1fd
Xint0x80_syscall() at Xint0x80_syscall+0x25
Debugger("panic")
Stopped at      Debugger+0x40:  pushl   $-0x1

The filesystem activity has a bunch of unwritten buffers. When soft
updates is enabled in this state, the iodone routine i
>How-To-Repeat:
fs is the name of a filesystem. If you do these four steps, you will
panic the system.

mount /fs
tar cvfz foo.tgz /usr/lib
mount -u -o rdonly /fs
tunefs -n enable /fs

You will trip into this problem after a bunch of tries. I can successfully
reproduce this approx 20% of the time.
>Fix:

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

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