> Date: Wed, 3 Mar 2021 10:27:34 +0100
> From: Martin Pieuchot <m...@openbsd.org>
>
> On 24/02/21(Wed) 11:33, Martin Pieuchot wrote:
> > As soon as the upper part of the page fault handler is executed w/o
> > KERNEL_LOCK(), uvm_anfree_list() will also be executed without it.
> >
> > To not corrupt the value of `uvmexp.swpgonly' counter, use atomic
> > operations to modify it.
> >
> > ok?
>
> Anyone?
ok kettenis@
P.S. I'm still looking at the pagedaemon locking diff; that one
doesn't look ok to me at first sight.
> > Index: uvm/uvm_anon.c
> > ===================================================================
> > RCS file: /cvs/src/sys/uvm/uvm_anon.c,v
> > retrieving revision 1.51
> > diff -u -p -r1.51 uvm_anon.c
> > --- uvm/uvm_anon.c 19 Jan 2021 13:21:36 -0000 1.51
> > +++ uvm/uvm_anon.c 24 Feb 2021 09:48:41 -0000
> > @@ -120,9 +120,9 @@ uvm_anfree_list(struct vm_anon *anon, st
> > }
> > } else {
> > if (anon->an_swslot != 0) {
> > - /* this page is no longer only in swap. */
> > + /* This page is no longer only in swap. */
> > KASSERT(uvmexp.swpgonly > 0);
> > - uvmexp.swpgonly--;
> > + atomic_dec_int(&uvmexp.swpgonly);
> > }
> > }
> > anon->an_lock = NULL;
> > Index: uvm/uvm_aobj.c
> > ===================================================================
> > RCS file: /cvs/src/sys/uvm/uvm_aobj.c,v
> > retrieving revision 1.90
> > diff -u -p -r1.90 uvm_aobj.c
> > --- uvm/uvm_aobj.c 11 Jan 2021 18:51:09 -0000 1.90
> > +++ uvm/uvm_aobj.c 24 Feb 2021 09:50:39 -0000
> > @@ -381,7 +381,7 @@ uao_free(struct uvm_aobj *aobj)
> > * this page is no longer
> > * only in swap.
> > */
> > - uvmexp.swpgonly--;
> > + atomic_dec_int(&uvmexp.swpgonly);
> > }
> >
> > next = LIST_NEXT(elt, list);
> > @@ -400,7 +400,7 @@ uao_free(struct uvm_aobj *aobj)
> > if (slot) {
> > uvm_swap_free(slot, 1);
> > /* this page is no longer only in swap. */
> > - uvmexp.swpgonly--;
> > + atomic_dec_int(&uvmexp.swpgonly);
> > }
> > }
> > free(aobj->u_swslots, M_UVMAOBJ, aobj->u_pages * sizeof(int));
> > @@ -1549,6 +1549,6 @@ uao_dropswap_range(struct uvm_object *uo
> > */
> > if (swpgonlydelta > 0) {
> > KASSERT(uvmexp.swpgonly >= swpgonlydelta);
> > - uvmexp.swpgonly -= swpgonlydelta;
> > + atomic_add_int(&uvmexp.swpgonly, -swpgonlydelta);
> > }
> > }
> > Index: uvm/uvm_km.c
> > ===================================================================
> > RCS file: /cvs/src/sys/uvm/uvm_km.c,v
> > retrieving revision 1.139
> > diff -u -p -r1.139 uvm_km.c
> > --- uvm/uvm_km.c 15 Dec 2020 22:14:42 -0000 1.139
> > +++ uvm/uvm_km.c 24 Feb 2021 09:52:19 -0000
> > @@ -242,6 +242,7 @@ uvm_km_pgremove(struct uvm_object *uobj,
> > struct vm_page *pp;
> > voff_t curoff;
> > int slot;
> > + int swpgonlydelta = 0;
> >
> > KASSERT(uobj->pgops == &aobj_pager);
> >
> > @@ -262,8 +263,13 @@ uvm_km_pgremove(struct uvm_object *uobj,
> > uvm_pagefree(pp);
> > uvm_unlock_pageq();
> > } else if (slot != 0) {
> > - uvmexp.swpgonly--;
> > + swpgonlydelta++;
> > }
> > + }
> > +
> > + if (swpgonlydelta > 0) {
> > + KASSERT(uvmexp.swpgonly >= swpgonlydelta);
> > + atomic_add_int(&uvmexp.swpgonly, -swpgonlydelta);
> > }
> > }
> >
> > Index: uvm/uvm_pdaemon.c
> > ===================================================================
> > RCS file: /cvs/src/sys/uvm/uvm_pdaemon.c,v
> > retrieving revision 1.88
> > diff -u -p -r1.88 uvm_pdaemon.c
> > --- uvm/uvm_pdaemon.c 24 Nov 2020 13:49:09 -0000 1.88
> > +++ uvm/uvm_pdaemon.c 24 Feb 2021 09:53:48 -0000
> > @@ -485,7 +485,7 @@ uvmpd_scan_inactive(struct pglist *pglst
> > if (p->pg_flags & PG_CLEAN) {
> > if (p->pg_flags & PQ_SWAPBACKED) {
> > /* this page now lives only in swap */
> > - uvmexp.swpgonly++;
> > + atomic_inc_int(&uvmexp.swpgonly);
> > }
> >
> > /* zap all mappings with pmap_page_protect... */
> > @@ -963,7 +963,7 @@ uvmpd_drop(struct pglist *pglst)
> > if (p->pg_flags & PG_CLEAN) {
> > if (p->pg_flags & PQ_SWAPBACKED) {
> > /* this page now lives only in swap */
> > - uvmexp.swpgonly++;
> > + atomic_inc_int(&uvmexp.swpgonly);
> > }
> >
> > /* zap all mappings with pmap_page_protect... */
> > Index: uvm/uvm_swap.c
> > ===================================================================
> > RCS file: /cvs/src/sys/uvm/uvm_swap.c,v
> > retrieving revision 1.148
> > diff -u -p -r1.148 uvm_swap.c
> > --- uvm/uvm_swap.c 14 Dec 2020 13:29:18 -0000 1.148
> > +++ uvm/uvm_swap.c 24 Feb 2021 09:55:36 -0000
> > @@ -1574,14 +1574,14 @@ uvm_swap_get(struct vm_page *page, int s
> >
> > KERNEL_LOCK();
> > /* this page is (about to be) no longer only in swap. */
> > - uvmexp.swpgonly--;
> > + atomic_dec_int(uvmexp.swpgonly);
> >
> > result = uvm_swap_io(&page, swslot, 1, B_READ |
> > ((flags & PGO_SYNCIO) ? 0 : B_ASYNC));
> >
> > if (result != VM_PAGER_OK && result != VM_PAGER_PEND) {
> > /* oops, the read failed so it really is still only in swap. */
> > - uvmexp.swpgonly++;
> > + atomic_inc_int(&uvmexp.swpgonly);
> > }
> > KERNEL_UNLOCK();
> > return (result);
> > Index: uvm/uvmexp.h
> > ===================================================================
> > RCS file: /cvs/src/sys/uvm/uvmexp.h,v
> > retrieving revision 1.8
> > diff -u -p -r1.8 uvmexp.h
> > --- uvm/uvmexp.h 28 Dec 2020 14:01:23 -0000 1.8
> > +++ uvm/uvmexp.h 24 Feb 2021 09:56:06 -0000
> > @@ -41,6 +41,7 @@
> > * other than the vm system.
> > *
> > * Locks used to protect struct members in this file:
> > + * a atomic operations
> > * I immutable after creation
> > * K kernel lock
> > * F uvm_lock_fpageq
> > @@ -82,7 +83,7 @@ struct uvmexp {
> > int nswapdev; /* number of configured swap devices in system */
> > int swpages; /* [K] number of PAGE_SIZE'ed swap pages */
> > int swpginuse; /* number of swap pages in use */
> > - int swpgonly; /* [K] number of swap pages in use, not also in RAM */
> > + int swpgonly; /* [a] number of swap pages in use, not also in RAM */
> > int nswget; /* number of swap pages moved from disk to RAM */
> > int nanon; /* XXX number total of anon's in system */
> > int unused05; /* formerly nanonneeded */
>
>
