misc/68757: rapid file creation on snapshotted filesystems panics lockmgr

[John Kozubik]

>Number:         68757
>Category:       misc
>Synopsis:       rapid file creation on snapshotted filesystems panics lockmgr
>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 Jul 07 06:40:24 GMT 2004
>Closed-Date:
>Last-Modified:
>Originator:     John Kozubik
>Release:        FreeBSD 5.2.1-RELEASE
>Organization:
http://www.kozubik.com
>Environment:
FreeBSD kozubik 5.2.1-RELEASE FreeBSD 5.2.1-RELEASE #0: Mon Feb 23 20:45:55 GMT 2004     root at wv1u.btc.adaptec.com:/usr/obj/usr/src/sys/GENERIC  i386 
>Description:
Rapid file creation on filesystems with as few as one snapshot on them
will panic lockmgr:

panic: lockmgr: locking against myself
cpuid = 0;

syncing disks, buffers remaining... panic: ffs_copyonwrite: recursive call
cpuid = 0;
uptime: 5m10s
Shutting down ACPI

(crash)
>How-To-Repeat:
Here is how you can quickly recreate this problem:

mksnap_ffs /mnt/mount1 /mnt/mount1/snapshot_1
cd /mnt/mount1
tar cvf /mnt/mount1/devel.tar /usr/ports/devel
tar xvf devel.tar

You will crash the system and (possibly) receive the above output within
seconds.

I have repeated this problem on both a laptop and a server, with both IDE
and SCSI disks, and with both a GENERIC and a pared down kernel (no
additions, simply subtractions).  Further, disabling ACPI by adding
hint.acpi.0.disabled="1" to the file /boot/loader.conf did not help in any
way.  All tested systems were single processor Pentium-3 systems.
>Fix:
No known fix or workaround, other than to avoid creating snapshots on filesystems.
>Release-Note:
>Audit-Trail:
>Unformatted: