rw_enter(9) can sleep. When the lock is finally acquired by the
pagedaemon the previous check might no longer be true and the page
could be busy. In this case we shouldn't touch it.
Diff below recheck for PG_BUSY after acquiring the lock and also
use a variable for the lock to reduce the differences with NetBSD.
ok?
Index: uvm/uvm_pdaemon.c
===================================================================
RCS file: /cvs/src/sys/uvm/uvm_pdaemon.c,v
retrieving revision 1.96
diff -u -p -r1.96 uvm_pdaemon.c
--- uvm/uvm_pdaemon.c 11 Apr 2022 16:43:49 -0000 1.96
+++ uvm/uvm_pdaemon.c 28 Apr 2022 10:22:52 -0000
@@ -879,6 +879,8 @@ uvmpd_scan(void)
int free, inactive_shortage, swap_shortage, pages_freed;
struct vm_page *p, *nextpg;
struct uvm_object *uobj;
+ struct vm_anon *anon;
+ struct rwlock *slock;
boolean_t got_it;
MUTEX_ASSERT_LOCKED(&uvm.pageqlock);
@@ -947,20 +949,34 @@ uvmpd_scan(void)
p != NULL && (inactive_shortage > 0 || swap_shortage > 0);
p = nextpg) {
nextpg = TAILQ_NEXT(p, pageq);
-
- /* skip this page if it's busy. */
- if (p->pg_flags & PG_BUSY)
+ if (p->pg_flags & PG_BUSY) {
continue;
+ }
- if (p->pg_flags & PQ_ANON) {
- KASSERT(p->uanon != NULL);
- if (rw_enter(p->uanon->an_lock, RW_WRITE|RW_NOSLEEP))
+ /*
+ * lock the page's owner.
+ */
+ if (p->uobject != NULL) {
+ uobj = p->uobject;
+ slock = uobj->vmobjlock;
+ if (rw_enter(slock, RW_WRITE|RW_NOSLEEP)) {
continue;
+ }
} else {
- KASSERT(p->uobject != NULL);
- if (rw_enter(p->uobject->vmobjlock,
- RW_WRITE|RW_NOSLEEP))
+ anon = p->uanon;
+ KASSERT(p->uanon != NULL);
+ slock = anon->an_lock;
+ if (rw_enter(slock, RW_WRITE|RW_NOSLEEP)) {
continue;
+ }
+ }
+
+ /*
+ * skip this page if it's busy.
+ */
+ if ((p->pg_flags & PG_BUSY) != 0) {
+ rw_exit(slock);
+ continue;
}
/*
@@ -997,10 +1013,11 @@ uvmpd_scan(void)
uvmexp.pddeact++;
inactive_shortage--;
}
- if (p->pg_flags & PQ_ANON)
- rw_exit(p->uanon->an_lock);
- else
- rw_exit(p->uobject->vmobjlock);
+
+ /*
+ * we're done with this page.
+ */
+ rw_exit(slock);
}
}
