svn commit: r216703 - head/sys/i386/xen

Colin Percival cperciva at
Sun Dec 26 13:05:43 UTC 2010

Author: cperciva
Date: Sun Dec 26 13:05:43 2010
New Revision: 216703

  Lock the vm page queue mutex in pmap_pte_release around the call
  to PMAP_SET_VA; this fixes a mutex-not-held panic when a process
  which called mlock(2) exits, and parallels a change made in
  pmap_pte 10 months ago (svn r204160).
  Note: The locking in this code is utterly broken.  We should not
  be using the VM page queue mutex to protect the queue of pending
  Xen page mapping hypervisor calls.  Even if it made sense to do
  so, this commit and r204160 introduce LORs between the vm page
  queue mutex and PMAP2mutex.
  (However, a possible deadlock is better than a guaranteed panic,
  and this change will hopefully make life easier for whoever fixes
  the Xen pmap locking in the future.)
  PR:		kern/140313
  MFC after:	3 days


Modified: head/sys/i386/xen/pmap.c
--- head/sys/i386/xen/pmap.c	Sun Dec 26 01:42:52 2010	(r216702)
+++ head/sys/i386/xen/pmap.c	Sun Dec 26 13:05:43 2010	(r216703)
@@ -1015,7 +1015,9 @@ pmap_pte_release(pt_entry_t *pte)
 	if ((pt_entry_t *)((vm_offset_t)pte & ~PAGE_MASK) == PADDR2) {
 		CTR1(KTR_PMAP, "pmap_pte_release: pte=0x%jx",
+		vm_page_lock_queues();
+		vm_page_unlock_queues();

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