FW: [Xen-devel] Xen-unstable panic: FATAL PAGE FAULT

[MaoXiaoyun <tinnycloud@xxxxxxxxxxx>]

Forward the tested patch to anyone interested.
 
> Date: Tue, 7 Sep 2010 05:57:11 -0700
> Subject: Re: [Xen-devel] Xen-unstable panic: FATAL PAGE FAULT
> From: keir.fraser@xxxxxxxxxxxxx
> To: tinnycloud@xxxxxxxxxxx; JBeulich@xxxxxxxxxx
> CC: keir.fraser@xxxxxxxxxxxxx
>
> On 07/09/2010 05:19, "MaoXiaoyun" <tinnycloud@xxxxxxxxxxx> wrote:
>
> > It looks like the free_heap_pages can be invoked concurrently, right?
> > If so, suppose there are two domains run into this function, run to
> > line 546-548,
> > we can see that pg[i].count_info will be either set to PGC_state_offlined,
> > PGC_state_free,
> > and remember this is not locked by heap_lock(in fact the lock starts at line
> > 558).
> > Then it is possible that, one domain set one page to PGC_state_free, while
> > another domain
> > happened run to line 580, and its pg-mask is the same page that first domain
> > just freed,
> > sure the page is not in heap yet. Thus causes xen panic.
>
> Yes, I think this is it! The dumb patch (attached) is just to extend the
> locked region in alloc_ and free_heap_pages to include the for loops which
> update each page's state. A cleverer version would only need to update the
> first page in an aligned extent with the lock held, but it's not clear that
> buys us that much, especially in free_heap_pages() which usually gets called
> on single pages anyway.
>
> Please try the attached fix and see how you get on. I'm very confident it
> will fix the bug. Well caught!
>
> Thanks,
> Keir
>
>
> > 531 for ( i = 0; i < (1 << order); i++ )
> > 532 {
> > 533 /*
> > 534 * Cannot assume that count_info == 0, as there are some corner
> > case s
> > 535 * where it isn't the case and yet it isn't a bug:
> > 536 * 1. page_get_owner() is NULL
> > 537 * 2. page_get_owner() is a domain that was never accessible by
> > 538 * its domid (e.g., failed to fully construct the domain).
> > 539 * 3. page was never addressable by the guest (e.g., it's an
> > 540 * auto-translate-physmap guest and the page was never
> > included
> > 541 * in its pseudophysical address space).
> > 542 * In all the above cases there can be no guest mappings of this
> > page.
> > 543 */
> > 544 ASSERT(!page_state_is(&pg[i], offlined));
> > 545 pg[i].count_info =
> > 546 ((pg[i].count_info & PGC_broken) |
> > 547 (page_state_is(&pg[i], offlining)
> > 548 ? PGC_state_offlined : PGC_state_free));
> > 549 if ( page_state_is(&pg[i], offlined) )
> > 550 tainted = 1;
> > 5 51
> > 552 /* If a page has no owner it will need no safety TLB flush. */
> > 553 pg[i].u.free.need_tlbflush = (page_get_owner(&pg[i]) != NULL);
> > 554 if ( pg[i].u.free.need_tlbflush )
> > 555 pg[i].tlbflush_timestamp = tlbflush_current_time();
> > 556 }
> > 557
> > 558 spin_lock(&heap_lock);
> > 559
> > 560 avail[node][zone] += 1 << order;
> > 561 total_avail_pages += 1 << order;
> > 562
> > 563 if ( opt_tmem )
> > 564 midsize_alloc_zone_pages = max(
> > 565 midsize_alloc_zone_pages, total_avail_pages /
> > MIDSIZE_ALLOC_FRAC);
> > 566
> > 567 /* Merge chunks as far as possible. */
> > 568 while ( order < MAX_ORDER )
> > 569 {
> > 570 mask = 1UL << order;
> > 571
> > 572 if ( (page_to_mfn(pg) & mask) )
> > 573 {
> > 574 /* Merge with predecessor block? */
> > 575 if ( !mfn_valid(page_to_mfn(pg-mask)) ||
> > 576 !page_state_is(pg-mask, free) ||
> > 577 (PFN_ORDER(pg-mask) != order) )
> > 578 break;
> > 579
> > 580 pgn = pg - mask;
> > 581 head = &heap(node, zone, order);
> > 582 next = pdx_to_page(pgn->list.next);
> > 583 prev = pdx_to_page(pgn->list.prev);
> > 584 if((head->next == pgn) != (pgn->list.prev == PAGE_LIST_NULL)
> > ||
> > 585 (head->tail == pgn) != (pgn->list.next == PAGE_LIST_NULL))
> > {
> > 586 check_page(pg, pg-mask, mask, order, 1, zone, node,head);
> > 587 }
> > 588
> > 589 pg -= mask;
> > 590 page_list_del(pg, &heap(node, zone, order));
> > 591 }
> > 592 else
> > 593 {
> > 594 /* Merge with successor block? */
> > 595 if ( !mfn_valid(page_to_m fn(pg+mask)) ||
> > 596 !page_state_is(pg+mask, free) ||
> > 597 (PFN_ORDER(pg+mask) != order) )
> > 598 break;
> > 599
> > 600 pgn = pg + mask;
> > 601 head = &heap(node, zone, order);
> > 602 next = pdx_to_page(pgn->list.next);
> >
> >
> > From: tinnycloud@xxxxxxxxxxx
> > To: jbeulich@xxxxxxxxxx
> > CC: keir.fraser@xxxxxxxxxxxxx
> > Subject: RE: [Xen-devel] Xen-unstable panic: FATAL PAGE FAULT
> > Date: Tue, 7 Sep 2010 19:57:47 +0800
> >
> > Hi Jan:
> >
> > Thanks for your explainations.
> > I added the log on the page your required.
> >
> > ----------------------------check page---------------------------------
> > 502 static int check_page(struct page_info* pgb, struct page_info* pg,
> > unsigned long mask, unsigned int order, int i, int zone, int node, st ruct
> > page_list_ head *head){
> > 503
> > 504 printk("--------pgb %p, pg op mask %p, prev %p, next %p, \
> > 505 mask %lx, order %d, i %d zone %d node %d\n",
> > 506 pgb, pg, pdx_to_page(pg->list.prev),
> > pdx_to_page(pg->list.next),
> > 507 mask, order, i, zone, node);
> > 508 printk("--------head->next %p head->tail %p \n", head->next,
> > head->tail);
> > 509 printk("shr_handle %lu count_info %lu type_info %lu order %u
> > tlbflush_timestamp %u\n",
> > 510 pg->shr_handle, pg->count_info, pg->u.inuse.type_info,
> > pg->v.free.order, pg->tlbflush_timestamp);
> > 511
> > 512 panic("xmao id page before address assigned \n");
> > 513 return 0;
> > 514 }
> >
> > In addtion, I go through the code today. Well, I have another
> > question, in free_heap_pages, refer to
> > below, line 545 to 548, it seems that here domain page is travelled and its
> > state is set either to
> > PGC_state_offlined, PGC_state_free, so could be existed there are two adjacent
> > pages both set to
> > PGC_state_free(that is pg1 = pg2 - mask, and both free). If so, both two pages
> > are not in heap page list,
> > then this situation satisfy the panic. Is this possible?
> >
> > 531 for ( i = 0; i < (1 << order); i++ )
> > 532 {
> > 533 /*
> > 534 * Cannot assume that count_info == 0, as there are some corner
> > cases
> > 535 * where it isn't the case and yet it isn't a bug:
> > 536 * 1. page_get_owner() is NULL
> > 537 * 2. page_get_owner() is a domain that was never accessible by
> > 538 * its domid (e.g., failed to fully construct the domain).
> > 539 * 3. page was never addressable by t he guest (e.g., it's an
> > 540 * auto-translate-physmap guest and the page was never
> > included
> > 541 * in its pseudophysical address space).
> > 542 * In all the above cases there can be no guest mappings of this
> > page.
> > 543 */
> > 544 ASSERT(!page_state_is(&pg[i], offlined));
> > 545 pg[i].count_info =
> > 546 ((pg[i].count_info & PGC_broken) |
> > 547 (page_state_is(&pg[i], offlining)
> > 548 ? PGC_state_offlined : PGC_state_free));
> > 549 if ( page_state_is(&pg[i], offlined) )
> > 550 tainted = 1;
> > 551
> > 552 /* If a page has no owner it will need no safety TLB flush. */
> > 553 pg[i].u.free.need_tlbflush = (page_get_owner(&pg[i]) != NULL);
> > 554 if ( pg[i].u.free.need_tlbflush )
> > 555 pg[i].tlbflush_timestamp = tlbflush_current_time();
> > 556 }
> >
> >> Date: Mon, 6 Sep 2010 14:13:00 +0100
> >> From: JBeulich@xxxxxxxxxx
> >> To: tinnycloud@xxxxxxxxxxx
> >> CC: keir.fraser@xxxxxxxxxxxxx
> >> Subject: RE: [Xen-devel] Xen-unstable panic: FATAL PAGE FAULT
> >>
> >>>>> On 06.09.10 at 14:20, MaoXiaoyun <tinnycloud@xxxxxxxxxxx> wrote:
> >>> A quick question for you, what is tainted refer to in below log?
> >>>
> >>> (XEN) ----[ Xen-4.0.0 x86_64 debug=n Not tainted ]----
> >>
> >> In Xen, this really doesn't mean much - it's a concept inherited from
> >> Linux trying to describe how "clean" the current instance is in terms
> >> of software or hardware events in the past that may have affected
> >> stability and/or supportability.
> >>
> >>> (XEN) --------pgb ffff82f6087f02e0, pg op mask ffff82f6087f0 2c0, prev
> >>> ffff8315ffffffe0, next ffff8315ffffffe0, mask 1, order 0, i 1
> >>> zone 22 node 1
> >>> (XEN) ------head->next 0000000000000000, head->tail 0000000000000000
> >>
> >> If that data is right, we basically have a page that is free but not
> >> on the respective heap's list. You will need to print the fields of
> >> the calculated (not the passed int) page's struct page_info (not
> >> just ->list.next and ->list.prev). Further, you should go hunt
> >> for that page across all heap lists, and print where you found it
> >> (or whether you didn't find it anywhere). That'll hopefully tell us
> >> whether the page's state is wrong or whether it got misplaced.
> >>
> >> But as you perhaps noticed the system died on the third of your
> >> prink()-s: You should not de-reference pdx_t o_page(pg->list.prev)
> >> and pdx_to_page(pg->list.next), the information won't tell us
> >> much anyway (I think the whole third printk() is pointless).
> >>
> >> Further, I only now noticed that you second call to check_page()
> >> uses an incorrect second arguments: You want to pass pgn (and
> >> you could make the first call do so too).
> >>
> >> Jan
> >>
> >
>

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