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Code Issues Releases Activity

Simplify vmspace_fork()'s control flow by copying immutable data before

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the vm map locks are acquired.  Also, eliminate redundant initialization
of the new vm map's timestamp.

Reviewed by:	kib
MFC after:	3 weeks
This commit is contained in:
Alan Cox 2012-02-25 17:49:59 +00:00
parent bb374ac283
commit 79e538388f
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=232160
1 changed files with 10 additions and 14 deletions
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24
sys/vm/vm_map.c
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@ -3082,27 +3082,25 @@ struct vmspace *
vmspace_fork(struct vmspace *vm1, vm_ooffset_t *fork_charge)
{
struct vmspace *vm2;
vm_map_t old_map = &vm1->vm_map;
vm_map_t new_map;
vm_map_entry_t old_entry;
vm_map_entry_t new_entry;
vm_map_t new_map, old_map;
vm_map_entry_t new_entry, old_entry;
vm_object_t object;
int locked;
vm_map_lock(old_map);
if (old_map->busy)
vm_map_wait_busy(old_map);
new_map = NULL; /* silence gcc */
old_map = &vm1->vm_map;
/* Copy immutable fields of vm1 to vm2. */
vm2 = vmspace_alloc(old_map->min_offset, old_map->max_offset);
if (vm2 == NULL)
goto unlock_and_return;
return (NULL);
vm2->vm_taddr = vm1->vm_taddr;
vm2->vm_daddr = vm1->vm_daddr;
vm2->vm_maxsaddr = vm1->vm_maxsaddr;
new_map = &vm2->vm_map; /* XXX */
vm_map_lock(old_map);
if (old_map->busy)
vm_map_wait_busy(old_map);
new_map = &vm2->vm_map;
locked = vm_map_trylock(new_map); /* trylock to silence WITNESS */
KASSERT(locked, ("vmspace_fork: lock failed"));
new_map->timestamp = 1;
old_entry = old_map->header.next;
@ -3223,15 +3221,13 @@ vmspace_fork(struct vmspace *vm1, vm_ooffset_t *fork_charge)
}
old_entry = old_entry->next;
}
unlock_and_return:
/*
* Use inlined vm_map_unlock() to postpone handling the deferred
* map entries, which cannot be done until both old_map and
* new_map locks are released.
*/
sx_xunlock(&old_map->lock);
if (vm2 != NULL)
sx_xunlock(&new_map->lock);
sx_xunlock(&new_map->lock);
vm_map_process_deferred();
return (vm2);