[PATCH 1/3 gnumach] vm_map: Fix deadlock in vm code

[Damien Zammit]

Authored-by: Sergey Bugaev <bugaevc@gmail.com>
---
 vm/vm_map.c | 32 ++++++++++++++++++++++----------
 1 file changed, 22 insertions(+), 10 deletions(-)

diff --git a/vm/vm_map.c b/vm/vm_map.c
index f221c532..e4672260 100644
--- a/vm/vm_map.c
+++ b/vm/vm_map.c
@@ -1424,8 +1424,9 @@ vm_map_pageable_scan(struct vm_map *map,
                     struct vm_map_entry *start,
                     struct vm_map_entry *end)
 {
-       struct vm_map_entry *entry;
-       boolean_t do_wire_faults;
+       struct vm_map_entry     *entry;
+       struct vm_map_entry     entry_copy;
+       boolean_t               do_wire_faults;
 
        /*
         * Pass 1. Update counters and prepare wiring faults.
@@ -1549,15 +1550,30 @@ vm_map_pageable_scan(struct vm_map *map,
         * while we have it unlocked.  We cannot trust user threads
         * to do the same.
         *
+        * Once we unlock the map, even well-intentioned operations
+        * on adjacent VM regions can end up affecting our entry,
+        * due to clipping and coalescing entries.  So, make a
+        * temporary copy of the entry, and pass that to vm_fault_wire()
+        * instead of the original.
+        *
         * HACK HACK HACK HACK
         */
        if (vm_map_pmap(map) == kernel_pmap) {
+               /*
+                *      TODO: Support wiring more than one entry
+                *      in the kernel map at a time.
+                */
+               assert(start->vme_next == end);
+               entry_copy = *start;
                vm_map_unlock(map); /* trust me ... */
-       } else {
-               vm_map_lock_set_recursive(map);
-               vm_map_lock_write_to_read(map);
+               vm_fault_wire(map, &entry_copy);
+               vm_map_lock(map);
+               return;
        }
 
+       vm_map_lock_set_recursive(map);
+       vm_map_lock_write_to_read(map);
+
        for (entry = start; entry != end; entry = entry->vme_next) {
                /*
                 * The wiring count can only be 1 if it was
@@ -1572,11 +1588,7 @@ vm_map_pageable_scan(struct vm_map *map,
                }
        }
 
-       if (vm_map_pmap(map) == kernel_pmap) {
-               vm_map_lock(map);
-       } else {
-               vm_map_lock_clear_recursive(map);
-       }
+       vm_map_lock_clear_recursive(map);
 }
 
 /*
-- 
2.43.0