Date: Thu, 22 May 2003 18:11:33 +1000 From: Tim Robbins <tjr@FreeBSD.ORG> To: current@freebsd.org Subject: VM-related lock order reversal Message-ID: <20030522181133.A32602@dilbert.robbins.dropbear.id.au>
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Got this today while stressing the system out, trying to reproduce a nullfs
deadlock:
lock order reversal
1st 0xc103d940 vm object (vm object) @ /usr/p4/tjr/src/sys/vm/vm_map.c:2148
2nd 0xc042f110 system map (system map) @ /usr/p4/tjr/src/sys/vm/vm_kern.c:325
In case the line numbers in my tree are slightly out of sync:
vm_map.c:2148 is in vm_map_delete():
2143 if (object->ref_count != 1 &&
2144 (object->flags & (OBJ_NOSPLIT|OBJ_ONEMAPPING)) == OBJ_ONEMAPPING &&
2145 (object->type == OBJT_DEFAULT || object->type == OBJT_SWAP)) {
2146 VM_OBJECT_UNLOCK(object);
2147 vm_object_collapse(object);
2148 VM_OBJECT_LOCK(object);
2149 vm_object_page_remove(object, offidxstart, offidxend, FALSE);
2150 if (object->type == OBJT_SWAP)
2151 swap_pager_freespace(object, offidxstart, count);
vm_kern.c:325 is in kmem_malloc():
320 /*
321 * Locate sufficient space in the map. This will give us the final
322 * virtual address for the new memory, and thus will tell us the
323 * offset within the kernel map.
324 */
325 vm_map_lock(map);
326 if (vm_map_findspace(map, vm_map_min(map), size, &addr)) {
327 vm_map_unlock(map);
328 if (map != kmem_map) {
329 static int last_report; /* when we did it (in ticks) */
Kernel config is GENERIC minus a few things, plus WITNESS, WITNESS_SKIPSPIN,
INVARIANTS, INVARIANTS_SUPPORT, DEBUG_VFS_LOCKS, and DIAGNOSTIC.
Tim
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