Subject: kern/6641: mount_mfs can cause UVM crash
To: None <>
From: Matthias Scheler <>
List: netbsd-bugs
Date: 12/24/1998 01:48:44
>Number:         6641
>Category:       kern
>Synopsis:       mount_mfs can cause UVM crash
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people (Kernel Bug People)
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Dec 23 17:05:01 1998
>Originator:     Matthias Scheler
Matthias Scheler                      
>Release:        981223
System: NetBSD 1.3I NetBSD 1.3I (LYSSA) #0: Wed Dec 23 11:36:07 MET 1998 i386

After replacing two 400MB swap partitions with a single 750MB one my system
started crashing while mounting a memory filesystem on "/tmp" somewhere
in the UVM code. Here's the output of DDB's trace command:

_amap_copy(fcffc204,fd0043fc,1,1,1e000) at _amap_copy+0x245
_uvm_fault(fcffc204,1e000,0,3,0) at _uvm_fault+0x163
_trap() at _trap+0x41b

The "fstab" looked like this:

/dev/sd0b       none            swap    sw
/dev/sd0b       /tmp            mfs     rw

By reducing the size of the memory filesystem to 512MB the problem can be
avoided completely. With a size between about 600 and 700MB the system
doesn't crash but "mount_mfs" hangs forever.

If it matters:
It's a Pentium II based system with 256MB main memory. 40% of the memory
are used for filesystem buffers.

Try to mount a memory filesystem on a swap partition with a size above 750MB.

Sorry, I don't know.