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Avoid lock-order reversal between the vm object list mutex and the vm

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object mutex.
This commit is contained in:
Alan Cox 2004-01-02 19:38:25 +00:00
parent 277b62040d
commit e0ba75dd78
1 changed files with 15 additions and 5 deletions
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20
sys/vm/vm_meter.c
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@ -100,7 +100,14 @@ vmtotal(SYSCTL_HANDLER_ARGS)
GIANT_REQUIRED;
mtx_lock(&vm_object_list_mtx);
TAILQ_FOREACH(object, &vm_object_list, object_list) {
VM_OBJECT_LOCK(object);
if (!VM_OBJECT_TRYLOCK(object)) {
/*
* Avoid a lock-order reversal. Consequently,
* the reported number of active pages may be
* greater than the actual number.
*/
continue;
}
vm_object_clear_flag(object, OBJ_ACTIVE);
VM_OBJECT_UNLOCK(object);
}
@ -176,12 +183,16 @@ vmtotal(SYSCTL_HANDLER_ARGS)
*/
mtx_lock(&vm_object_list_mtx);
TAILQ_FOREACH(object, &vm_object_list, object_list) {
VM_OBJECT_LOCK(object);
/*
* devices, like /dev/mem, will badly skew our totals
* Perform unsynchronized reads on the object to avoid
* a lock-order reversal. In this case, the lack of
* synchronization should not impair the accuracy of
* the reported statistics.
*/
if (object->type == OBJT_DEVICE) {
VM_OBJECT_UNLOCK(object);
/*
* Devices, like /dev/mem, will badly skew our totals.
*/
continue;
}
totalp->t_vm += object->size;
@ -199,7 +210,6 @@ vmtotal(SYSCTL_HANDLER_ARGS)
totalp->t_armshr += object->resident_page_count;
}
}
VM_OBJECT_UNLOCK(object);
}
mtx_unlock(&vm_object_list_mtx);
totalp->t_free = cnt.v_free_count + cnt.v_cache_count;