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Since r218070 reenabled the call to vm_map_simplify_entry() from

Browse Source 
vm_map_insert(), the kmem_back() assumption about newly inserted
entry might be broken due to interference of two factors. In the low
memory condition, when vm_page_alloc() returns NULL, supplied map is
unlocked. If another thread performs kmem_malloc() meantime, and its
map entry is placed right next to our thread map entry in the map,
both entries wire count is still 0 and entries are coalesced due to
vm_map_simplify_entry().

Mark new entry with MAP_ENTRY_IN_TRANSITION to prevent coalesce.
Fix some style issues, tighten the assertions to account for
MAP_ENTRY_IN_TRANSITION state.

Reported and tested by:	pho
Reviewed by:	alc
This commit is contained in:
Konstantin Belousov 2011-02-15 09:03:58 +00:00
parent c43728a230
commit 56bdf2dbc2
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=218701
1 changed files with 23 additions and 9 deletions
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32
sys/vm/vm_kern.c
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@ -353,12 +353,24 @@ kmem_back(vm_map_t map, vm_offset_t addr, vm_size_t size, int flags)
vm_map_entry_t entry;
vm_page_t m;
int pflags;
boolean_t found;
KASSERT(vm_map_locked(map), ("kmem_back: map %p is not locked", map));
offset = addr - VM_MIN_KERNEL_ADDRESS;
vm_object_reference(kmem_object);
vm_map_insert(map, kmem_object, offset, addr, addr + size,
VM_PROT_ALL, VM_PROT_ALL, 0);
VM_PROT_ALL, VM_PROT_ALL, 0);
/*
* Assert: vm_map_insert() will never be able to extend the
* previous entry so vm_map_lookup_entry() will find a new
* entry exactly corresponding to this address range and it
* will have wired_count == 0.
*/
found = vm_map_lookup_entry(map, addr, &entry);
KASSERT(found && entry->start == addr && entry->end == addr + size &&
entry->wired_count == 0 && (entry->eflags & MAP_ENTRY_IN_TRANSITION)
== 0, ("kmem_back: entry not found or misaligned"));
if ((flags & (M_NOWAIT|M_USE_RESERVE)) == M_NOWAIT)
pflags = VM_ALLOC_INTERRUPT | VM_ALLOC_WIRED;
@ -381,9 +393,15 @@ kmem_back(vm_map_t map, vm_offset_t addr, vm_size_t size, int flags)
if (m == NULL) {
if ((flags & M_NOWAIT) == 0) {
VM_OBJECT_UNLOCK(kmem_object);
entry->eflags |= MAP_ENTRY_IN_TRANSITION;
vm_map_unlock(map);
VM_WAIT;
vm_map_lock(map);
KASSERT(
(entry->eflags & (MAP_ENTRY_IN_TRANSITION | MAP_ENTRY_NEEDS_WAKEUP)) ==
MAP_ENTRY_IN_TRANSITION,
("kmem_back: volatile entry"));
entry->eflags &= ~MAP_ENTRY_IN_TRANSITION;
VM_OBJECT_LOCK(kmem_object);
goto retry;
}
@ -413,15 +431,11 @@ kmem_back(vm_map_t map, vm_offset_t addr, vm_size_t size, int flags)
VM_OBJECT_UNLOCK(kmem_object);
/*
* Mark map entry as non-pageable. Assert: vm_map_insert() will never
* be able to extend the previous entry so there will be a new entry
* exactly corresponding to this address range and it will have
* wired_count == 0.
* Mark map entry as non-pageable. Repeat the assert.
*/
if (!vm_map_lookup_entry(map, addr, &entry) ||
entry->start != addr || entry->end != addr + size ||
entry->wired_count != 0)
panic("kmem_malloc: entry not found or misaligned");
KASSERT(entry->start == addr && entry->end == addr + size &&
entry->wired_count == 0,
("kmem_back: entry not found or misaligned after allocation"));
entry->wired_count = 1;
/*