If an anon is associated with a page, acquire its lock before any modification.

This change should have been part of the previous anon-locking diff and is
necessary to run the top part of uvm_fault() unlocked.

ok jmatthew@

diff --git a/sys/uvm/uvm_pdaemon.c b/sys/uvm/uvm_pdaemon.c
index ea0bd2e..5892059 100644 (file)
--- a/sys/uvm/uvm_pdaemon.c
+++ b/sys/uvm/uvm_pdaemon.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: uvm_pdaemon.c,v 1.88 2020/11/24 13:49:09 mpi Exp $    */
+/*     $OpenBSD: uvm_pdaemon.c,v 1.89 2021/03/01 09:13:33 mpi Exp $    */
 /*     $NetBSD: uvm_pdaemon.c,v 1.23 2000/08/20 10:24:14 bjh21 Exp $   */
 
 /* 
@@ -460,7 +460,13 @@ uvmpd_scan_inactive(struct pglist *pglst)
                        if (p->pg_flags & PQ_ANON) {
                                anon = p->uanon;
                                KASSERT(anon != NULL);
+                               if (rw_enter(anon->an_lock,
+                                   RW_WRITE|RW_NOSLEEP)) {
+                                       /* lock failed, skip this page */
+                                       continue;
+                               }
                                if (p->pg_flags & PG_BUSY) {
+                                       rw_exit(anon->an_lock);
                                        uvmexp.pdbusy++;
                                        /* someone else owns page, skip it */
                                        continue;
@@ -504,6 +510,7 @@ uvmpd_scan_inactive(struct pglist *pglst)
 
                                        /* remove from object */
                                        anon->an_page = NULL;
+                                       rw_exit(anon->an_lock);
                                }
                                continue;
                        }
@@ -513,6 +520,9 @@ uvmpd_scan_inactive(struct pglist *pglst)
                         * free target when all the current pageouts complete.
                         */
                        if (free + uvmexp.paging > uvmexp.freetarg << 2) {
+                               if (anon) {
+                                       rw_exit(anon->an_lock);
+                               }
                                continue;
                        }
 
@@ -525,6 +535,9 @@ uvmpd_scan_inactive(struct pglist *pglst)
                        if ((p->pg_flags & PQ_SWAPBACKED) && uvm_swapisfull()) {
                                dirtyreacts++;
                                uvm_pageactivate(p);
+                               if (anon) {
+                                       rw_exit(anon->an_lock);
+                               }
                                continue;
                        }
 
@@ -591,6 +604,8 @@ uvmpd_scan_inactive(struct pglist *pglst)
                                                    &p->pg_flags,
                                                    PG_BUSY);
                                                UVM_PAGE_OWN(p, NULL);
+                                               if (anon)
+                                                       rw_exit(anon->an_lock);
                                                continue;
                                        }
                                        swcpages = 0;   /* cluster is empty */
@@ -622,6 +637,9 @@ uvmpd_scan_inactive(struct pglist *pglst)
                 */
                if (swap_backed) {
                        if (p) {        /* if we just added a page to cluster */
+                               if (anon)
+                                       rw_exit(anon->an_lock);
+
                                /* cluster not full yet? */
                                if (swcpages < swnpages)
                                        continue;
@@ -730,6 +748,12 @@ uvmpd_scan_inactive(struct pglist *pglst)
                        /* relock p's object: page queues not lock yet, so
                         * no need for "try" */
 
+                       /* !swap_backed case: already locked... */
+                       if (swap_backed) {
+                               if (anon)
+                                       rw_enter(anon->an_lock, RW_WRITE);
+                       }
+
 #ifdef DIAGNOSTIC
                        if (result == VM_PAGER_UNLOCK)
                                panic("pagedaemon: pageout returned "
@@ -754,6 +778,7 @@ uvmpd_scan_inactive(struct pglist *pglst)
                                anon->an_page = NULL;
                                p->uanon = NULL;
 
+                               rw_exit(anon->an_lock);
                                uvm_anfree(anon);       /* kills anon */
                                pmap_page_protect(p, PROT_NONE);
                                anon = NULL;
@@ -787,6 +812,8 @@ uvmpd_scan_inactive(struct pglist *pglst)
                         * the inactive queue can't be re-queued [note: not
                         * true for active queue]).
                         */
+                       if (anon)
+                               rw_exit(anon->an_lock);
 
                        if (nextpg && (nextpg->pg_flags & PQ_INACTIVE) == 0) {
                                nextpg = TAILQ_FIRST(pglst);    /* reload! */
@@ -893,9 +920,11 @@ uvmpd_scan(void)
                if (p->pg_flags & PG_BUSY)
                        continue;
 
-               if (p->pg_flags & PQ_ANON)
+               if (p->pg_flags & PQ_ANON) {
                        KASSERT(p->uanon != NULL);
-               else
+                       if (rw_enter(p->uanon->an_lock, RW_WRITE|RW_NOSLEEP))
+                               continue;
+               } else
                        KASSERT(p->uobject != NULL);
 
                /*
@@ -932,6 +961,8 @@ uvmpd_scan(void)
                        uvmexp.pddeact++;
                        inactive_shortage--;
                }
+               if (p->pg_flags & PQ_ANON)
+                       rw_exit(p->uanon->an_lock);
        }
 }