Re: kernel oops on mmotm-2015-10-15-15-20
From: Kirill A. Shutemov
Date: Mon Nov 02 2015 - 08:03:04 EST
On Fri, Oct 30, 2015 at 04:03:50PM +0900, Minchan Kim wrote:
> On Thu, Oct 29, 2015 at 11:52:06AM +0200, Kirill A. Shutemov wrote:
> > On Thu, Oct 29, 2015 at 04:58:29PM +0900, Minchan Kim wrote:
> > > On Thu, Oct 29, 2015 at 02:25:24AM +0200, Kirill A. Shutemov wrote:
> > > > On Thu, Oct 22, 2015 at 06:00:51PM +0900, Minchan Kim wrote:
> > > > > On Thu, Oct 22, 2015 at 10:21:36AM +0900, Minchan Kim wrote:
> > > > > > Hello Hugh,
> > > > > >
> > > > > > On Wed, Oct 21, 2015 at 05:59:59PM -0700, Hugh Dickins wrote:
> > > > > > > On Thu, 22 Oct 2015, Minchan Kim wrote:
> > > > > > > >
> > > > > > > > I added the code to check it and queued it again but I had another oops
> > > > > > > > in this time but symptom is related to anon_vma, too.
> > > > > > > > (kernel is based on recent mmotm + unconditional mkdirty for bug fix)
> > > > > > > > It seems page_get_anon_vma returns NULL since the page was not page_mapped
> > > > > > > > at that time but second check of page_mapped right before try_to_unmap seems
> > > > > > > > to be true.
> > > > > > > >
> > > > > > > > Adding 4191228k swap on /dev/vda5. Priority:-1 extents:1 across:4191228k FS
> > > > > > > > Adding 4191228k swap on /dev/vda5. Priority:-1 extents:1 across:4191228k FS
> > > > > > > > page:ffffea0001cfbfc0 count:3 mapcount:1 mapping:ffff88007f1b5f51 index:0x600000aff
> > > > > > > > flags: 0x4000000000048019(locked|uptodate|dirty|swapcache|swapbacked)
> > > > > > > > page dumped because: VM_BUG_ON_PAGE(PageAnon(page) && !PageKsm(page) && !anon_vma)
> > > > > > >
> > > > > > > That's interesting, that's one I added in my page migration series.
> > > > > > > Let me think on it, but it could well relate to the one you got before.
> > > > > >
> > > > > > I will roll back to mm/madv_free-v4.3-rc5-mmotm-2015-10-15-15-20
> > > > > > instead of next-20151021 to remove noise from your migration cleanup
> > > > > > series and will test it again.
> > > > > > If it is fixed, I will test again with your migration patchset, then.
> > > > >
> > > > > I tested mmotm-2015-10-15-15-20 with test program I attach for a long time.
> > > > > Therefore, there is no patchset from Hugh's migration patch in there.
> > > > > And I added below debug code with request from Kirill to all test kernels.
> > > >
> > > > It took too long time (and a lot of printk()), but I think I track it down
> > > > finally.
> > > >
> > > > The patch below seems fixes issue for me. It's not yet properly tested, but
> > > > looks like it works.
> > > >
> > > > The problem was my wrong assumption on how migration works: I thought that
> > > > kernel would wait migration to finish on before deconstruction mapping.
> > > >
> > > > But turn out that's not true.
> > > >
> > > > As result if zap_pte_range() races with split_huge_page(), we can end up
> > > > with page which is not mapped anymore but has _count and _mapcount
> > > > elevated. The page is on LRU too. So it's still reachable by vmscan and by
> > > > pfn scanners (Sasha showed few similar traces from compaction too).
> > > > It's likely that page->mapping in this case would point to freed anon_vma.
> > > >
> > > > BOOM!
> > > >
> > > > The patch modify freeze/unfreeze_page() code to match normal migration
> > > > entries logic: on setup we remove page from rmap and drop pin, on removing
> > > > we get pin back and put page on rmap. This way even if migration entry
> > > > will be removed under us we don't corrupt page's state.
> > > >
> > > > Please, test.
> > > >
> > >
> > > kernel: On mmotm-2015-10-15-15-20 + pte_mkdirty patch + your new patch, I tested
> > > one I sent to you(ie, oops.c + memcg_test.sh)
> > >
> > > page:ffffea00016a0000 count:3 mapcount:0 mapping:ffff88007f49d001 index:0x600001800 compound_mapcount: 0
> > > flags: 0x4000000000044009(locked|uptodate|head|swapbacked)
> > > page dumped because: VM_BUG_ON_PAGE(!page_mapcount(page))
> > > page->mem_cgroup:ffff88007f613c00
> >
> > Ignore my previous answer. Still sleeping.
> >
> > The right way to fix I think is something like:
> >
> > diff --git a/mm/rmap.c b/mm/rmap.c
> > index 35643176bc15..f2d46792a554 100644
> > --- a/mm/rmap.c
> > +++ b/mm/rmap.c
> > @@ -1173,20 +1173,12 @@ void do_page_add_anon_rmap(struct page *page,
> > bool compound = flags & RMAP_COMPOUND;
> > bool first;
> >
> > - if (PageTransCompound(page)) {
> > + if (PageTransCompound(page) && compound) {
> > + atomic_t *mapcount;
> > VM_BUG_ON_PAGE(!PageLocked(page), page);
> > - if (compound) {
> > - atomic_t *mapcount;
> > -
> > - VM_BUG_ON_PAGE(!PageTransHuge(page), page);
> > - mapcount = compound_mapcount_ptr(page);
> > - first = atomic_inc_and_test(mapcount);
> > - } else {
> > - /* Anon THP always mapped first with PMD */
> > - first = 0;
> > - VM_BUG_ON_PAGE(!page_mapcount(page), page);
> > - atomic_inc(&page->_mapcount);
> > - }
> > + VM_BUG_ON_PAGE(!PageTransHuge(page), page);
> > + mapcount = compound_mapcount_ptr(page);
> > + first = atomic_inc_and_test(mapcount);
> > } else {
> > VM_BUG_ON_PAGE(compound, page);
> > first = atomic_inc_and_test(&page->_mapcount);
> > --
>
> kernel: On mmotm-2015-10-15-15-20 + pte_mkdirty patch + freeze/unfreeze patch + above patch,
>
> Adding 4191228k swap on /dev/vda5. Priority:-1 extents:1 across:4191228k FS
> Adding 4191228k swap on /dev/vda5. Priority:-1 extents:1 across:4191228k FS
> Adding 4191228k swap on /dev/vda5. Priority:-1 extents:1 across:4191228k FS
> Adding 4191228k swap on /dev/vda5. Priority:-1 extents:1 across:4191228k FS
> Adding 4191228k swap on /dev/vda5. Priority:-1 extents:1 across:4191228k FS
> BUG: Bad rss-counter state mm:ffff880058d2e580 idx:1 val:512
> Adding 4191228k swap on /dev/vda5. Priority:-1 extents:1 across:4191228k FS
> Adding 4191228k swap on /dev/vda5. Priority:-1 extents:1 across:4191228k FS
>
> <SNIP>
>
> Adding 4191228k swap on /dev/vda5. Priority:-1 extents:1 across:4191228k FS
> Adding 4191228k swap on /dev/vda5. Priority:-1 extents:1 across:4191228k FS
> Adding 4191228k swap on /dev/vda5. Priority:-1 extents:1 across:4191228k FS
> BUG: Bad rss-counter state mm:ffff880046980700 idx:1 val:511
> BUG: Bad rss-counter state mm:ffff880046980700 idx:2 val:1
Hm. I was not able to trigger this and don't see anything obviuous what can
lead to this kind of missmatch :-/
I found one more bug: clearing of PageTail can be visible to other CPUs
before updated page->flags on the page.
I don't think this bug is connected to what you've reported, but worth
testing.
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 5e0fe82a0fae..12bd8c5a4409 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2934,6 +2934,13 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
smp_wmb(); /* make pte visible before pmd */
pmd_populate(mm, pmd, pgtable);
+
+ if (freeze) {
+ for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
+ page_remove_rmap(page + i, false);
+ put_page(page + i);
+ }
+ }
}
void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
@@ -3079,6 +3086,8 @@ static void freeze_page_vma(struct vm_area_struct *vma, struct page *page,
if (pte_soft_dirty(entry))
swp_pte = pte_swp_mksoft_dirty(swp_pte);
set_pte_at(vma->vm_mm, address, pte + i, swp_pte);
+ page_remove_rmap(page, false);
+ put_page(page);
}
pte_unmap_unlock(pte, ptl);
}
@@ -3117,8 +3126,6 @@ static void unfreeze_page_vma(struct vm_area_struct *vma, struct page *page,
return;
pte = pte_offset_map_lock(vma->vm_mm, pmd, address, &ptl);
for (i = 0; i < HPAGE_PMD_NR; i++, address += PAGE_SIZE, page++) {
- if (!page_mapped(page))
- continue;
if (!is_swap_pte(pte[i]))
continue;
@@ -3128,6 +3135,9 @@ static void unfreeze_page_vma(struct vm_area_struct *vma, struct page *page,
if (migration_entry_to_page(swp_entry) != page)
continue;
+ get_page(page);
+ page_add_anon_rmap(page, vma, address, false);
+
entry = pte_mkold(mk_pte(page, vma->vm_page_prot));
entry = pte_mkdirty(entry);
if (is_write_migration_entry(swp_entry))
@@ -3181,8 +3191,6 @@ static int __split_huge_page_tail(struct page *head, int tail,
*/
atomic_add(mapcount + 1, &page_tail->_count);
- /* after clearing PageTail the gup refcount can be released */
- smp_mb__after_atomic();
page_tail->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
page_tail->flags |= (head->flags &
@@ -3195,6 +3203,12 @@ static int __split_huge_page_tail(struct page *head, int tail,
(1L << PG_unevictable)));
page_tail->flags |= (1L << PG_dirty);
+ /*
+ * After clearing PageTail the gup refcount can be released.
+ * Page flags also must be visible before we make the page non-compound.
+ */
+ smp_wmb();
+
clear_compound_head(page_tail);
if (page_is_young(head))
diff --git a/mm/rmap.c b/mm/rmap.c
index 35643176bc15..e4f8d9fb1c3d 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1173,20 +1173,12 @@ void do_page_add_anon_rmap(struct page *page,
bool compound = flags & RMAP_COMPOUND;
bool first;
- if (PageTransCompound(page)) {
+ if (compound) {
+ atomic_t *mapcount;
VM_BUG_ON_PAGE(!PageLocked(page), page);
- if (compound) {
- atomic_t *mapcount;
-
- VM_BUG_ON_PAGE(!PageTransHuge(page), page);
- mapcount = compound_mapcount_ptr(page);
- first = atomic_inc_and_test(mapcount);
- } else {
- /* Anon THP always mapped first with PMD */
- first = 0;
- VM_BUG_ON_PAGE(!page_mapcount(page), page);
- atomic_inc(&page->_mapcount);
- }
+ VM_BUG_ON_PAGE(!PageTransHuge(page), page);
+ mapcount = compound_mapcount_ptr(page);
+ first = atomic_inc_and_test(mapcount);
} else {
VM_BUG_ON_PAGE(compound, page);
first = atomic_inc_and_test(&page->_mapcount);
@@ -1201,7 +1193,6 @@ void do_page_add_anon_rmap(struct page *page,
* disabled.
*/
if (compound) {
- VM_BUG_ON_PAGE(!PageTransHuge(page), page);
__inc_zone_page_state(page,
NR_ANON_TRANSPARENT_HUGEPAGES);
}
--
Kirill A. Shutemov
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