[Bug 258932] panic: vm_page_free_prep: freeing mapped page

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=258932

--- Comment #8 from Mark Johnston <markj@FreeBSD.org> ---
(In reply to Bryan Drewery from comment #7)
Thanks.  So it appears that the referencing pmap belongs to the parent process,
another tmux process:

db> show proc 1634
Process 1634 (tmux) at 0xfffff809dd32f000:
 state: NORMAL
 uid: 0  gids: 0, 0, 5, 65531, 65532
 parent: pid 1 at 0xfffff801140cf538
 ABI: FreeBSD ELF64
 flag: 0x10000000  flag2: 0
 arguments: tmux: server (/tmp/tmux-0/default)
 reaper: 0xfffff801140cf538 reapsubtree: 1
 sigparent: 20
 vmspace: 0xfffffe238e741000
   (map 0xfffffe238e741000)
   (map.pmap 0xfffffe238e7410c0)
   (pmap 0xfffffe238e741120)
 threads: 1
101736                   S       select  0xfffff80a3a993740  tmux

Switching to that thread,

db> show pte 0x811be5000                                                        
VA 0x0000000811be5000 pml4e 0x0000000338dad067 pdpe 0x0000000876895067 pde
0x000000077bde3067 pte 0x800000107d157425

So the PTE is indeed valid and the paddr matches that of the page in question.

Proc 1634 has a very very fragmented vm_map for some reason, tons of small map
entries.  I need to let "show procvm" run for a while to find the map entry
corresponding to 0x811be5000.

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