Re: [RFC][PATCH v1 02/11] mm: soft-offline: add missing error check of set_hwpoison_free_buddy_page()
On 11/13/2018 05:46 AM, Naoya Horiguchi wrote: > Hi Anshuman, > > On Fri, Nov 09, 2018 at 03:50:41PM +0530, Anshuman Khandual wrote: >> >> On 11/09/2018 12:17 PM, Naoya Horiguchi wrote: >>> set_hwpoison_free_buddy_page() could fail, then the target page is >>> finally not isolated, so it's better to report -EBUSY for userspace >>> to know the failure and chance of retry. >>> >> IIUC set_hwpoison_free_buddy_page() could only fail if the page is not >> free in the buddy. At least for soft_offline_huge_page() that wont be >> the case otherwise dissolve_free_huge_page() would have returned non >> zero -EBUSY. Is there any other reason set_hwpoison_free_buddy_page() >> would not succeed ? > There is a race window between page freeing (after successful soft-offline > -> page migration case) and the containment by set_hwpoison_free_buddy_page(). > Or a target page can be allocated just after get_any_page() decided that > the target page is a free page. > So set_hwpoison_free_buddy_page() would safely fail in such cases. Makes sense. Thanks.
Re: [RFC][PATCH v1 02/11] mm: soft-offline: add missing error check of set_hwpoison_free_buddy_page()
On 11/13/2018 05:46 AM, Naoya Horiguchi wrote: > Hi Anshuman, > > On Fri, Nov 09, 2018 at 03:50:41PM +0530, Anshuman Khandual wrote: >> >> On 11/09/2018 12:17 PM, Naoya Horiguchi wrote: >>> set_hwpoison_free_buddy_page() could fail, then the target page is >>> finally not isolated, so it's better to report -EBUSY for userspace >>> to know the failure and chance of retry. >>> >> IIUC set_hwpoison_free_buddy_page() could only fail if the page is not >> free in the buddy. At least for soft_offline_huge_page() that wont be >> the case otherwise dissolve_free_huge_page() would have returned non >> zero -EBUSY. Is there any other reason set_hwpoison_free_buddy_page() >> would not succeed ? > There is a race window between page freeing (after successful soft-offline > -> page migration case) and the containment by set_hwpoison_free_buddy_page(). > Or a target page can be allocated just after get_any_page() decided that > the target page is a free page. > So set_hwpoison_free_buddy_page() would safely fail in such cases. Makes sense. Thanks.
Re: [RFC][PATCH v1 02/11] mm: soft-offline: add missing error check of set_hwpoison_free_buddy_page()
Hi Anshuman, On Fri, Nov 09, 2018 at 03:50:41PM +0530, Anshuman Khandual wrote: > > > On 11/09/2018 12:17 PM, Naoya Horiguchi wrote: > > set_hwpoison_free_buddy_page() could fail, then the target page is > > finally not isolated, so it's better to report -EBUSY for userspace > > to know the failure and chance of retry. > > > > IIUC set_hwpoison_free_buddy_page() could only fail if the page is not > free in the buddy. At least for soft_offline_huge_page() that wont be > the case otherwise dissolve_free_huge_page() would have returned non > zero -EBUSY. Is there any other reason set_hwpoison_free_buddy_page() > would not succeed ? There is a race window between page freeing (after successful soft-offline -> page migration case) and the containment by set_hwpoison_free_buddy_page(). Or a target page can be allocated just after get_any_page() decided that the target page is a free page. So set_hwpoison_free_buddy_page() would safely fail in such cases. Thanks, Naoya Horiguchi > > > And for consistency, this patch moves set_hwpoison_free_buddy_page() > > in unmap_and_move() to __soft_offline_page(). > > Yeah this check should be handled in soft offline functions not inside > migrations they trigger. >
Re: [RFC][PATCH v1 02/11] mm: soft-offline: add missing error check of set_hwpoison_free_buddy_page()
Hi Anshuman, On Fri, Nov 09, 2018 at 03:50:41PM +0530, Anshuman Khandual wrote: > > > On 11/09/2018 12:17 PM, Naoya Horiguchi wrote: > > set_hwpoison_free_buddy_page() could fail, then the target page is > > finally not isolated, so it's better to report -EBUSY for userspace > > to know the failure and chance of retry. > > > > IIUC set_hwpoison_free_buddy_page() could only fail if the page is not > free in the buddy. At least for soft_offline_huge_page() that wont be > the case otherwise dissolve_free_huge_page() would have returned non > zero -EBUSY. Is there any other reason set_hwpoison_free_buddy_page() > would not succeed ? There is a race window between page freeing (after successful soft-offline -> page migration case) and the containment by set_hwpoison_free_buddy_page(). Or a target page can be allocated just after get_any_page() decided that the target page is a free page. So set_hwpoison_free_buddy_page() would safely fail in such cases. Thanks, Naoya Horiguchi > > > And for consistency, this patch moves set_hwpoison_free_buddy_page() > > in unmap_and_move() to __soft_offline_page(). > > Yeah this check should be handled in soft offline functions not inside > migrations they trigger. >
Re: [RFC][PATCH v1 02/11] mm: soft-offline: add missing error check of set_hwpoison_free_buddy_page()
On 11/09/2018 12:17 PM, Naoya Horiguchi wrote: > set_hwpoison_free_buddy_page() could fail, then the target page is > finally not isolated, so it's better to report -EBUSY for userspace > to know the failure and chance of retry. > IIUC set_hwpoison_free_buddy_page() could only fail if the page is not free in the buddy. At least for soft_offline_huge_page() that wont be the case otherwise dissolve_free_huge_page() would have returned non zero -EBUSY. Is there any other reason set_hwpoison_free_buddy_page() would not succeed ? > And for consistency, this patch moves set_hwpoison_free_buddy_page() > in unmap_and_move() to __soft_offline_page(). Yeah this check should be handled in soft offline functions not inside migrations they trigger.
Re: [RFC][PATCH v1 02/11] mm: soft-offline: add missing error check of set_hwpoison_free_buddy_page()
On 11/09/2018 12:17 PM, Naoya Horiguchi wrote: > set_hwpoison_free_buddy_page() could fail, then the target page is > finally not isolated, so it's better to report -EBUSY for userspace > to know the failure and chance of retry. > IIUC set_hwpoison_free_buddy_page() could only fail if the page is not free in the buddy. At least for soft_offline_huge_page() that wont be the case otherwise dissolve_free_huge_page() would have returned non zero -EBUSY. Is there any other reason set_hwpoison_free_buddy_page() would not succeed ? > And for consistency, this patch moves set_hwpoison_free_buddy_page() > in unmap_and_move() to __soft_offline_page(). Yeah this check should be handled in soft offline functions not inside migrations they trigger.
[RFC][PATCH v1 02/11] mm: soft-offline: add missing error check of set_hwpoison_free_buddy_page()
set_hwpoison_free_buddy_page() could fail, then the target page is
finally not isolated, so it's better to report -EBUSY for userspace
to know the failure and chance of retry.
And for consistency, this patch moves set_hwpoison_free_buddy_page()
in unmap_and_move() to __soft_offline_page().
Fixes: 6bc9b56433b7 ("mm: fix race on soft-offlining free huge pages")
Signed-off-by: Naoya Horiguchi
---
mm/memory-failure.c | 15 ---
mm/migrate.c| 9 -
2 files changed, 12 insertions(+), 12 deletions(-)
diff --git v4.19-mmotm-2018-10-30-16-08/mm/memory-failure.c
v4.19-mmotm-2018-10-30-16-08_patched/mm/memory-failure.c
index 9f09bf3..11e283e 100644
--- v4.19-mmotm-2018-10-30-16-08/mm/memory-failure.c
+++ v4.19-mmotm-2018-10-30-16-08_patched/mm/memory-failure.c
@@ -1719,14 +1719,18 @@ static int soft_offline_huge_page(struct page *page,
int flags)
/*
* We set PG_hwpoison only when the migration source hugepage
* was successfully dissolved, because otherwise hwpoisoned
-* hugepage remains on free hugepage list, then userspace will
-* find it as SIGBUS by allocation failure. That's not expected
-* in soft-offlining.
+* hugepage remains on free hugepage list. The allocator ignores
+* such a hwpoisoned page so it's never allocated, but it could
+* kill a process because of no-memory rather than hwpoison.
+* Soft-offline never impacts the userspace, so this is
+* undesired.
*/
ret = dissolve_free_huge_page(page);
if (!ret) {
if (set_hwpoison_free_buddy_page(page))
num_poisoned_pages_inc();
+ else
+ ret = -EBUSY;
}
}
return ret;
@@ -1804,6 +1808,11 @@ static int __soft_offline_page(struct page *page, int
flags)
pfn, ret, page->flags, >flags);
if (ret > 0)
ret = -EIO;
+ } else {
+ if (set_hwpoison_free_buddy_page(page))
+ num_poisoned_pages_inc();
+ else
+ ret = -EBUSY;
}
} else {
pr_info("soft offline: %#lx: isolation failed: %d, page count
%d, type %lx (%pGp)\n",
diff --git v4.19-mmotm-2018-10-30-16-08/mm/migrate.c
v4.19-mmotm-2018-10-30-16-08_patched/mm/migrate.c
index f7e4bfd..1742372 100644
--- v4.19-mmotm-2018-10-30-16-08/mm/migrate.c
+++ v4.19-mmotm-2018-10-30-16-08_patched/mm/migrate.c
@@ -1199,15 +1199,6 @@ static ICE_noinline int unmap_and_move(new_page_t
get_new_page,
*/
if (rc == MIGRATEPAGE_SUCCESS) {
put_page(page);
- if (reason == MR_MEMORY_FAILURE) {
- /*
-* Set PG_HWPoison on just freed page
-* intentionally. Although it's rather weird,
-* it's how HWPoison flag works at the moment.
-*/
- if (set_hwpoison_free_buddy_page(page))
- num_poisoned_pages_inc();
- }
} else {
if (rc != -EAGAIN) {
if (likely(!__PageMovable(page))) {
--
2.7.0
[RFC][PATCH v1 02/11] mm: soft-offline: add missing error check of set_hwpoison_free_buddy_page()
set_hwpoison_free_buddy_page() could fail, then the target page is
finally not isolated, so it's better to report -EBUSY for userspace
to know the failure and chance of retry.
And for consistency, this patch moves set_hwpoison_free_buddy_page()
in unmap_and_move() to __soft_offline_page().
Fixes: 6bc9b56433b7 ("mm: fix race on soft-offlining free huge pages")
Signed-off-by: Naoya Horiguchi
---
mm/memory-failure.c | 15 ---
mm/migrate.c| 9 -
2 files changed, 12 insertions(+), 12 deletions(-)
diff --git v4.19-mmotm-2018-10-30-16-08/mm/memory-failure.c
v4.19-mmotm-2018-10-30-16-08_patched/mm/memory-failure.c
index 9f09bf3..11e283e 100644
--- v4.19-mmotm-2018-10-30-16-08/mm/memory-failure.c
+++ v4.19-mmotm-2018-10-30-16-08_patched/mm/memory-failure.c
@@ -1719,14 +1719,18 @@ static int soft_offline_huge_page(struct page *page,
int flags)
/*
* We set PG_hwpoison only when the migration source hugepage
* was successfully dissolved, because otherwise hwpoisoned
-* hugepage remains on free hugepage list, then userspace will
-* find it as SIGBUS by allocation failure. That's not expected
-* in soft-offlining.
+* hugepage remains on free hugepage list. The allocator ignores
+* such a hwpoisoned page so it's never allocated, but it could
+* kill a process because of no-memory rather than hwpoison.
+* Soft-offline never impacts the userspace, so this is
+* undesired.
*/
ret = dissolve_free_huge_page(page);
if (!ret) {
if (set_hwpoison_free_buddy_page(page))
num_poisoned_pages_inc();
+ else
+ ret = -EBUSY;
}
}
return ret;
@@ -1804,6 +1808,11 @@ static int __soft_offline_page(struct page *page, int
flags)
pfn, ret, page->flags, >flags);
if (ret > 0)
ret = -EIO;
+ } else {
+ if (set_hwpoison_free_buddy_page(page))
+ num_poisoned_pages_inc();
+ else
+ ret = -EBUSY;
}
} else {
pr_info("soft offline: %#lx: isolation failed: %d, page count
%d, type %lx (%pGp)\n",
diff --git v4.19-mmotm-2018-10-30-16-08/mm/migrate.c
v4.19-mmotm-2018-10-30-16-08_patched/mm/migrate.c
index f7e4bfd..1742372 100644
--- v4.19-mmotm-2018-10-30-16-08/mm/migrate.c
+++ v4.19-mmotm-2018-10-30-16-08_patched/mm/migrate.c
@@ -1199,15 +1199,6 @@ static ICE_noinline int unmap_and_move(new_page_t
get_new_page,
*/
if (rc == MIGRATEPAGE_SUCCESS) {
put_page(page);
- if (reason == MR_MEMORY_FAILURE) {
- /*
-* Set PG_HWPoison on just freed page
-* intentionally. Although it's rather weird,
-* it's how HWPoison flag works at the moment.
-*/
- if (set_hwpoison_free_buddy_page(page))
- num_poisoned_pages_inc();
- }
} else {
if (rc != -EAGAIN) {
if (likely(!__PageMovable(page))) {
--
2.7.0
