amaps operation are already serialized by their own lock so it is
possible to free them w/o holding the KERNEL_LOCK(). This has been
tested by many as part of the UVM unlocking diff.
ok?
Index: uvm/uvm_map.c
===================================================================
RCS file: /cvs/src/sys/uvm/uvm_map.c,v
retrieving revision 1.277
diff -u -p -r1.277 uvm_map.c
--- uvm/uvm_map.c 17 Jun 2021 16:10:39 -0000 1.277
+++ uvm/uvm_map.c 1 Oct 2021 17:02:29 -0000
@@ -1570,9 +1570,15 @@ uvm_unmap_detach(struct uvm_map_deadq *d
int waitok = flags & UVM_PLA_WAITOK;
TAILQ_FOREACH_SAFE(entry, deadq, dfree.deadq, tmp) {
+ /* Drop reference to amap, if we've got one. */
+ if (entry->aref.ar_amap)
+ amap_unref(entry->aref.ar_amap,
+ entry->aref.ar_pageoff,
+ atop(entry->end - entry->start),
+ flags & AMAP_REFALL);
+
/* Skip entries for which we have to grab the kernel lock. */
- if (entry->aref.ar_amap || UVM_ET_ISSUBMAP(entry) ||
- UVM_ET_ISOBJ(entry))
+ if (UVM_ET_ISSUBMAP(entry) || UVM_ET_ISOBJ(entry))
continue;
TAILQ_REMOVE(deadq, entry, dfree.deadq);
@@ -1586,13 +1592,6 @@ uvm_unmap_detach(struct uvm_map_deadq *d
while ((entry = TAILQ_FIRST(deadq)) != NULL) {
if (waitok)
uvm_pause();
- /* Drop reference to amap, if we've got one. */
- if (entry->aref.ar_amap)
- amap_unref(entry->aref.ar_amap,
- entry->aref.ar_pageoff,
- atop(entry->end - entry->start),
- flags & AMAP_REFALL);
-
/* Drop reference to our backing object, if we've got one. */
if (UVM_ET_ISSUBMAP(entry)) {
/* ... unlikely to happen, but play it safe */
