bin/59988: undocumented panic with large malloc-backed md

[Colin Percival]

>Number:         59988
>Category:       bin
>Synopsis:       undocumented panic with large malloc-backed md
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          doc-bug
>Submitter-Id:   current-users
>Arrival-Date:   Sat Dec 06 01:40:16 PST 2003
>Closed-Date:
>Last-Modified:
>Originator:     Colin Percival
>Release:        
>Organization:
>Environment:
>Description:

  Large malloc-backed memory disks will cause 5.x systems to panic when they 
are filled.  This isn't documented anywhere.

>How-To-Repeat:

mdconfig -a -t malloc -s 300M -u 0
dd if=/dev/zero of=/dev/md0 bs=1048576 count=300
<do anything which requires kernel memory>

>Fix:

  Document the panic in mdconfig.8

--- src/sbin/mdconfig/mdconfig.8.orig   Sat Dec  6 09:20:15 2003
+++ src/sbin/mdconfig/mdconfig.8        Sat Dec  6 09:26:44 2003
@@ -91,6 +91,11 @@
 Storage for this type of memory disk is allocated with
 .Xr malloc 9 .
 This limits the size to the malloc bucket limit in the kernel.
+If the
+.Fl o Cm reserve
+option is not set, creating and filling a large
+malloc-backed memory disk is a very easy way to
+panic a system.
 .It Cm vnode
 A file specified with
 .Fl f Ar file
>Release-Note:
>Audit-Trail:
>Unformatted: