[DragonFlyBSD - Bug #3433] (New) vm_map: use normal COW inheritance for user-wired mappings

[sigttou]

Issue #3433 has been reported by sigttou.

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Bug #3433: vm_map: use normal COW inheritance for user-wired mappings
http://bugs.dragonflybsd.org/issues/3433

* Author: sigttou
* Status: New
* Priority: Normal
* Category: Kernel
* Target version: 6.6
* Start date: 2026-10-03
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Forking an mlock()ed MAP_PRIVATE file mapping can panic with "vm_fault_copy_wired: page missing". The wired-copy path expects the page in the front object, but it may be in a backing object or have been removed after the file was truncated.

Use normal COW inheritance for normal mappings with only a user wire. The parent stays user-wired and the child remains unwired. The normal fault path resolves backing pages and handles pager errors. Keep eager copying for hard-wired and virtual-page-table mappings.

---Files--------------------------------
0003-vm-map-user-wired-fork-cow.patch (1.54 KB)


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