[mm-unstable PATCH v6 0/8] mm, hwpoison: enable 1GB hugepage support (v6)

[mm-unstable PATCH v6 0/8] mm, hwpoison: enable 1GB hugepage support (v6)

[Naoya Horiguchi]

Here is v6 of "enabling memory error handling on 1GB hugepage" patchset.

I applied feedbacks provided for v5 (thank you, Miaohe).
All changes (on 1/8, 3/8, and 4/8) are minor ones.

- v1: https://lore.kernel.org/linux-mm/20220602050631.771414-1-naoya.horiguchi@linux.dev/T/#u
- v2: https://lore.kernel.org/linux-mm/20220623235153.2623702-1-naoya.horiguchi@linux.dev/T/#u
- v3: https://lore.kernel.org/linux-mm/20220630022755.3362349-1-naoya.horiguchi@linux.dev/T/#u
- v4: https://lore.kernel.org/linux-mm/20220704013312.2415700-1-naoya.horiguchi@linux.dev/T/#u
- v5: https://lore.kernel.org/linux-mm/20220708053653.964464-1-naoya.horiguchi@linux.dev/T/#u

Thanks,
Naoya Horiguchi
---
Summary:

Naoya Horiguchi (8):
      mm/hugetlb: check gigantic_page_runtime_supported() in return_unused_surplus_pages()
      mm/hugetlb: make pud_huge() and follow_huge_pud() aware of non-present pud entry
      mm, hwpoison, hugetlb: support saving mechanism of raw error pages
      mm, hwpoison: make unpoison aware of raw error info in hwpoisoned hugepage
      mm, hwpoison: set PG_hwpoison for busy hugetlb pages
      mm, hwpoison: make __page_handle_poison returns int
      mm, hwpoison: skip raw hwpoison page in freeing 1GB hugepage
      mm, hwpoison: enable memory error handling on 1GB hugepage

 arch/x86/mm/hugetlbpage.c |   8 ++-
 include/linux/hugetlb.h   |  17 ++++-
 include/linux/mm.h        |   2 +-
 include/linux/swapops.h   |   9 +++
 include/ras/ras_event.h   |   1 -
 mm/hugetlb.c              |  58 +++++++++++++----
 mm/memory-failure.c       | 162 +++++++++++++++++++++++++++++++++++++---------
 7 files changed, 209 insertions(+), 48 deletions(-)

[mm-unstable PATCH v6 1/8] mm/hugetlb: check gigantic_page_runtime_supported() in return_unused_surplus_pages()

[Naoya Horiguchi]

From: Naoya Horiguchi <naoya.horiguchi@nec.com>

I found a weird state of 1GB hugepage pool, caused by the following
procedure:

  - run a process reserving all free 1GB hugepages,
  - shrink free 1GB hugepage pool to zero (i.e. writing 0 to
    /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages), then
  - kill the reserving process.

, then all the hugepages are free *and* surplus at the same time.

  $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages
  3
  $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/free_hugepages
  3
  $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/resv_hugepages
  0
  $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/surplus_hugepages
  3

This state is resolved by reserving and allocating the pages then
freeing them again, so this seems not to result in serious problem.
But it's a little surprising (shrinking pool suddenly fails).

This behavior is caused by hstate_is_gigantic() check in
return_unused_surplus_pages(). This was introduced so long ago in 2008
by commit aa888a74977a ("hugetlb: support larger than MAX_ORDER"), and
at that time the gigantic pages were not supposed to be allocated/freed
at run-time.  Now kernel can support runtime allocation/free, so let's
check gigantic_page_runtime_supported() together.

Signed-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
---
v4 -> v5:
- drop additional gigantic_page_runtime_supported() checks.

v2 -> v3:
- Fixed typo in patch description,
- add !gigantic_page_runtime_supported() check instead of removing
  hstate_is_gigantic() check (suggested by Miaohe and Muchun)
- add a few more !gigantic_page_runtime_supported() check in
  set_max_huge_pages() (by Mike).
---
 mm/hugetlb.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index a4506ed1f1db..cf8ccee7654c 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2432,8 +2432,7 @@ static void return_unused_surplus_pages(struct hstate *h,
 	/* Uncommit the reservation */
 	h->resv_huge_pages -= unused_resv_pages;
 
-	/* Cannot return gigantic pages currently */
-	if (hstate_is_gigantic(h))
+	if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported())
 		goto out;
 
 	/*
-- 
2.25.1

[mm-unstable PATCH v6 2/8] mm/hugetlb: make pud_huge() and follow_huge_pud() aware of non-present pud entry

[Naoya Horiguchi]

From: Naoya Horiguchi <naoya.horiguchi@nec.com>

follow_pud_mask() does not support non-present pud entry now.  As long as
I tested on x86_64 server, follow_pud_mask() still simply returns
no_page_table() for non-present_pud_entry() due to pud_bad(), so no severe
user-visible effect should happen.  But generally we should call
follow_huge_pud() for non-present pud entry for 1GB hugetlb page.

Update pud_huge() and follow_huge_pud() to handle non-present pud entries.
The changes are similar to previous works for pud entries commit e66f17ff7177
("mm/hugetlb: take page table lock in follow_huge_pmd()") and commit
cbef8478bee5 ("mm/hugetlb: pmd_huge() returns true for non-present hugepage").

Signed-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
---
v2 -> v3:
- fixed typos in subject and description,
- added comment on pud_huge(),
- added comment about fallback for hwpoisoned entry,
- updated initial check about FOLL_{PIN,GET} flags.
---
 arch/x86/mm/hugetlbpage.c |  8 +++++++-
 mm/hugetlb.c              | 32 ++++++++++++++++++++++++++++++--
 2 files changed, 37 insertions(+), 3 deletions(-)

diff --git a/arch/x86/mm/hugetlbpage.c b/arch/x86/mm/hugetlbpage.c
index 509408da0da1..6b3033845c6d 100644
--- a/arch/x86/mm/hugetlbpage.c
+++ b/arch/x86/mm/hugetlbpage.c
@@ -30,9 +30,15 @@ int pmd_huge(pmd_t pmd)
 		(pmd_val(pmd) & (_PAGE_PRESENT|_PAGE_PSE)) != _PAGE_PRESENT;
 }
 
+/*
+ * pud_huge() returns 1 if @pud is hugetlb related entry, that is normal
+ * hugetlb entry or non-present (migration or hwpoisoned) hugetlb entry.
+ * Otherwise, returns 0.
+ */
 int pud_huge(pud_t pud)
 {
-	return !!(pud_val(pud) & _PAGE_PSE);
+	return !pud_none(pud) &&
+		(pud_val(pud) & (_PAGE_PRESENT|_PAGE_PSE)) != _PAGE_PRESENT;
 }
 
 #ifdef CONFIG_HUGETLB_PAGE
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index cf8ccee7654c..77119d93a0f9 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -6978,10 +6978,38 @@ struct page * __weak
 follow_huge_pud(struct mm_struct *mm, unsigned long address,
 		pud_t *pud, int flags)
 {
-	if (flags & (FOLL_GET | FOLL_PIN))
+	struct page *page = NULL;
+	spinlock_t *ptl;
+	pte_t pte;
+
+	if (WARN_ON_ONCE(flags & FOLL_PIN))
 		return NULL;
 
-	return pte_page(*(pte_t *)pud) + ((address & ~PUD_MASK) >> PAGE_SHIFT);
+retry:
+	ptl = huge_pte_lock(hstate_sizelog(PUD_SHIFT), mm, (pte_t *)pud);
+	if (!pud_huge(*pud))
+		goto out;
+	pte = huge_ptep_get((pte_t *)pud);
+	if (pte_present(pte)) {
+		page = pud_page(*pud) + ((address & ~PUD_MASK) >> PAGE_SHIFT);
+		if (WARN_ON_ONCE(!try_grab_page(page, flags))) {
+			page = NULL;
+			goto out;
+		}
+	} else {
+		if (is_hugetlb_entry_migration(pte)) {
+			spin_unlock(ptl);
+			__migration_entry_wait(mm, (pte_t *)pud, ptl);
+			goto retry;
+		}
+		/*
+		 * hwpoisoned entry is treated as no_page_table in
+		 * follow_page_mask().
+		 */
+	}
+out:
+	spin_unlock(ptl);
+	return page;
 }
 
 struct page * __weak
-- 
2.25.1

[mm-unstable PATCH v6 3/8] mm, hwpoison, hugetlb: support saving mechanism of raw error pages

[Naoya Horiguchi]

From: Naoya Horiguchi <naoya.horiguchi@nec.com>

When handling memory error on a hugetlb page, the error handler tries to
dissolve and turn it into 4kB pages.  If it's successfully dissolved,
PageHWPoison flag is moved to the raw error page, so that's all right.
However, dissolve sometimes fails, then the error page is left as
hwpoisoned hugepage. It's useful if we can retry to dissolve it to save
healthy pages, but that's not possible now because the information about
where the raw error pages is lost.

Use the private field of a few tail pages to keep that information.  The
code path of shrinking hugepage pool uses this info to try delayed dissolve.
In order to remember multiple errors in a hugepage, a singly-linked list
originated from SUBPAGE_INDEX_HWPOISON-th tail page is constructed.  Only
simple operations (adding an entry or clearing all) are required and the
list is assumed not to be very long, so this simple data structure should
be enough.

If we failed to save raw error info, the hwpoison hugepage has errors on
unknown subpage, then this new saving mechanism does not work any more,
so disable saving new raw error info and freeing hwpoison hugepages.

Signed-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
Reported-by: kernel test robot <lkp@intel.com>
---
v5 -> v6:
- remove additional buggy HPageRawHwpUnreliable check

v4 -> v5:
- fixed build error (reported by kernel test robot).
- do not try to undo remove_hugetlb_page() when HPageRawHwpUnreliable is true,
- check HPageRawHwpUnreliable() before hugetlb_vmemmap_restore(),
- call num_poisoned_pages_inc() in hugetlb_set_page_hwpoison() when kalloc
  succeeds,
- remove "inline" in the definition of hugetlb_clear_page_hwpoison().

v3 -> v4:
- resolve conflict with "mm: hugetlb_vmemmap: improve hugetlb_vmemmap
  code readability", use hugetlb_vmemmap_restore() instead of
  hugetlb_vmemmap_alloc().

v2 -> v3:
- remove duplicate "return ret" lines,
- use GFP_ATOMIC instead of GFP_KERNEL,
- introduce HPageRawHwpUnreliable pseudo flag (suggested by Muchun),
- hugetlb_clear_page_hwpoison removes raw_hwp_page list even if
  HPageRawHwpUnreliable is true, (by Miaohe)

v1 -> v2:
- support hwpoison hugepage with multiple errors,
- moved the new interface functions to mm/memory-failure.c,
- define additional subpage index SUBPAGE_INDEX_HWPOISON_UNRELIABLE,
- stop freeing/dissolving hwpoison hugepages with unreliable raw error info,
- drop hugetlb_clear_page_hwpoison() in dissolve_free_huge_page() because
  that's done in update_and_free_page(),
- move setting/clearing PG_hwpoison flag to the new interfaces,
- checking already hwpoisoned or not on a subpage basis.

ChangeLog since previous post on 4/27:
- fixed typo in patch description (by Miaohe)
- fixed config value in #ifdef statement (by Miaohe)
- added sentences about "multiple hwpoison pages" scenario in patch
  description
---
 include/linux/hugetlb.h | 17 ++++++++-
 mm/hugetlb.c            | 23 +++++++-----
 mm/memory-failure.c     | 78 +++++++++++++++++++++++++++++++++++++++--
 3 files changed, 105 insertions(+), 13 deletions(-)

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 6d0620edf0a6..3ec981a0d8b3 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -42,6 +42,9 @@ enum {
 	SUBPAGE_INDEX_CGROUP,		/* reuse page->private */
 	SUBPAGE_INDEX_CGROUP_RSVD,	/* reuse page->private */
 	__MAX_CGROUP_SUBPAGE_INDEX = SUBPAGE_INDEX_CGROUP_RSVD,
+#endif
+#ifdef CONFIG_MEMORY_FAILURE
+	SUBPAGE_INDEX_HWPOISON,
 #endif
 	__NR_USED_SUBPAGE,
 };
@@ -551,7 +554,7 @@ generic_hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
  *	Synchronization:  Initially set after new page allocation with no
  *	locking.  When examined and modified during migration processing
  *	(isolate, migrate, putback) the hugetlb_lock is held.
- * HPG_temporary - - Set on a page that is temporarily allocated from the buddy
+ * HPG_temporary - Set on a page that is temporarily allocated from the buddy
  *	allocator.  Typically used for migration target pages when no pages
  *	are available in the pool.  The hugetlb free page path will
  *	immediately free pages with this flag set to the buddy allocator.
@@ -561,6 +564,8 @@ generic_hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
  * HPG_freed - Set when page is on the free lists.
  *	Synchronization: hugetlb_lock held for examination and modification.
  * HPG_vmemmap_optimized - Set when the vmemmap pages of the page are freed.
+ * HPG_raw_hwp_unreliable - Set when the hugetlb page has a hwpoison sub-page
+ *     that is not tracked by raw_hwp_page list.
  */
 enum hugetlb_page_flags {
 	HPG_restore_reserve = 0,
@@ -568,6 +573,7 @@ enum hugetlb_page_flags {
 	HPG_temporary,
 	HPG_freed,
 	HPG_vmemmap_optimized,
+	HPG_raw_hwp_unreliable,
 	__NR_HPAGEFLAGS,
 };
 
@@ -614,6 +620,7 @@ HPAGEFLAG(Migratable, migratable)
 HPAGEFLAG(Temporary, temporary)
 HPAGEFLAG(Freed, freed)
 HPAGEFLAG(VmemmapOptimized, vmemmap_optimized)
+HPAGEFLAG(RawHwpUnreliable, raw_hwp_unreliable)
 
 #ifdef CONFIG_HUGETLB_PAGE
 
@@ -796,6 +803,14 @@ extern int dissolve_free_huge_page(struct page *page);
 extern int dissolve_free_huge_pages(unsigned long start_pfn,
 				    unsigned long end_pfn);
 
+#ifdef CONFIG_MEMORY_FAILURE
+extern void hugetlb_clear_page_hwpoison(struct page *hpage);
+#else
+static inline void hugetlb_clear_page_hwpoison(struct page *hpage)
+{
+}
+#endif
+
 #ifdef CONFIG_ARCH_ENABLE_HUGEPAGE_MIGRATION
 #ifndef arch_hugetlb_migration_supported
 static inline bool arch_hugetlb_migration_supported(struct hstate *h)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 77119d93a0f9..e590632bc70f 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1535,6 +1535,13 @@ static void __update_and_free_page(struct hstate *h, struct page *page)
 	if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported())
 		return;
 
+	/*
+	 * If we don't know which subpages are hwpoisoned, we can't free
+	 * the hugepage, so it's leaked intentionally.
+	 */
+	if (HPageRawHwpUnreliable(page))
+		return;
+
 	if (hugetlb_vmemmap_restore(h, page)) {
 		spin_lock_irq(&hugetlb_lock);
 		/*
@@ -1547,6 +1554,13 @@ static void __update_and_free_page(struct hstate *h, struct page *page)
 		return;
 	}
 
+	/*
+	 * Move PageHWPoison flag from head page to the raw error pages,
+	 * which makes any healthy subpages reusable.
+	 */
+	if (unlikely(PageHWPoison(page)))
+		hugetlb_clear_page_hwpoison(page);
+
 	for (i = 0; i < pages_per_huge_page(h);
 	     i++, subpage = mem_map_next(subpage, page, i)) {
 		subpage->flags &= ~(1 << PG_locked | 1 << PG_error |
@@ -2109,15 +2123,6 @@ int dissolve_free_huge_page(struct page *page)
 		 */
 		rc = hugetlb_vmemmap_restore(h, head);
 		if (!rc) {
-			/*
-			 * Move PageHWPoison flag from head page to the raw
-			 * error page, which makes any subpages rather than
-			 * the error page reusable.
-			 */
-			if (PageHWPoison(head) && page != head) {
-				SetPageHWPoison(page);
-				ClearPageHWPoison(head);
-			}
 			update_and_free_page(h, head, false);
 		} else {
 			spin_lock_irq(&hugetlb_lock);
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index c9931c676335..74195c181d69 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1664,6 +1664,79 @@ int mf_dax_kill_procs(struct address_space *mapping, pgoff_t index,
 EXPORT_SYMBOL_GPL(mf_dax_kill_procs);
 #endif /* CONFIG_FS_DAX */
 
+#ifdef CONFIG_HUGETLB_PAGE
+/*
+ * Struct raw_hwp_page represents information about "raw error page",
+ * constructing singly linked list originated from ->private field of
+ * SUBPAGE_INDEX_HWPOISON-th tail page.
+ */
+struct raw_hwp_page {
+	struct llist_node node;
+	struct page *page;
+};
+
+static inline struct llist_head *raw_hwp_list_head(struct page *hpage)
+{
+	return (struct llist_head *)&page_private(hpage + SUBPAGE_INDEX_HWPOISON);
+}
+
+static int hugetlb_set_page_hwpoison(struct page *hpage, struct page *page)
+{
+	struct llist_head *head;
+	struct raw_hwp_page *raw_hwp;
+	struct llist_node *t, *tnode;
+	int ret = TestSetPageHWPoison(hpage) ? -EHWPOISON : 0;
+
+	/*
+	 * Once the hwpoison hugepage has lost reliable raw error info,
+	 * there is little meaning to keep additional error info precisely,
+	 * so skip to add additional raw error info.
+	 */
+	if (HPageRawHwpUnreliable(hpage))
+		return -EHWPOISON;
+	head = raw_hwp_list_head(hpage);
+	llist_for_each_safe(tnode, t, head->first) {
+		struct raw_hwp_page *p = container_of(tnode, struct raw_hwp_page, node);
+
+		if (p->page == page)
+			return -EHWPOISON;
+	}
+
+	raw_hwp = kmalloc(sizeof(struct raw_hwp_page), GFP_ATOMIC);
+	if (raw_hwp) {
+		raw_hwp->page = page;
+		llist_add(&raw_hwp->node, head);
+		/* the first error event will be counted in action_result(). */
+		if (ret)
+			num_poisoned_pages_inc();
+	} else {
+		/*
+		 * Failed to save raw error info.  We no longer trace all
+		 * hwpoisoned subpages, and we need refuse to free/dissolve
+		 * this hwpoisoned hugepage.
+		 */
+		SetHPageRawHwpUnreliable(hpage);
+	}
+	return ret;
+}
+
+void hugetlb_clear_page_hwpoison(struct page *hpage)
+{
+	struct llist_head *head;
+	struct llist_node *t, *tnode;
+
+	if (!HPageRawHwpUnreliable(hpage))
+		ClearPageHWPoison(hpage);
+	head = raw_hwp_list_head(hpage);
+	llist_for_each_safe(tnode, t, head->first) {
+		struct raw_hwp_page *p = container_of(tnode, struct raw_hwp_page, node);
+
+		SetPageHWPoison(p->page);
+		kfree(p);
+	}
+	llist_del_all(head);
+}
+
 /*
  * Called from hugetlb code with hugetlb_lock held.
  *
@@ -1698,7 +1771,7 @@ int __get_huge_page_for_hwpoison(unsigned long pfn, int flags)
 		goto out;
 	}
 
-	if (TestSetPageHWPoison(head)) {
+	if (hugetlb_set_page_hwpoison(head, page)) {
 		ret = -EHWPOISON;
 		goto out;
 	}
@@ -1710,7 +1783,6 @@ int __get_huge_page_for_hwpoison(unsigned long pfn, int flags)
 	return ret;
 }
 
-#ifdef CONFIG_HUGETLB_PAGE
 /*
  * Taking refcount of hugetlb pages needs extra care about race conditions
  * with basic operations like hugepage allocation/free/demotion.
@@ -1751,7 +1823,7 @@ static int try_memory_failure_hugetlb(unsigned long pfn, int flags, int *hugetlb
 	lock_page(head);
 
 	if (hwpoison_filter(p)) {
-		ClearPageHWPoison(head);
+		hugetlb_clear_page_hwpoison(head);
 		res = -EOPNOTSUPP;
 		goto out;
 	}
-- 
2.25.1

[mm-unstable PATCH v6 4/8] mm, hwpoison: make unpoison aware of raw error info in hwpoisoned hugepage

[Naoya Horiguchi]

From: Naoya Horiguchi <naoya.horiguchi@nec.com>

Raw error info list needs to be removed when hwpoisoned hugetlb is
unpoisoned.  And unpoison handler needs to know how many errors there
are in the target hugepage. So add them.

HPageVmemmapOptimized(hpage) and HPageRawHwpUnreliable(hpage)) can't be
unpoisoned, so let's skip them.

Signed-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
Reported-by: kernel test robot <lkp@intel.com>
---
v5 -> v6:
- set type of return value of hugetlb_clear_page_hwpoison() to void
- change type of return value of hugetlb_clear_page_hwpoison() to unsigned long

v4 -> v5:
- fix type of return value of free_raw_hwp_pages()
  (found by kernel test robot),
- prevent unpoison for HPageVmemmapOptimized and HPageRawHwpUnreliable.
---
 include/linux/swapops.h |  9 ++++++++
 mm/memory-failure.c     | 46 ++++++++++++++++++++++++++++++++++++-----
 2 files changed, 50 insertions(+), 5 deletions(-)

diff --git a/include/linux/swapops.h b/include/linux/swapops.h
index a01aeb3fcc0b..ddc98f96ad2c 100644
--- a/include/linux/swapops.h
+++ b/include/linux/swapops.h
@@ -498,6 +498,11 @@ static inline void num_poisoned_pages_dec(void)
 	atomic_long_dec(&num_poisoned_pages);
 }
 
+static inline void num_poisoned_pages_sub(long i)
+{
+	atomic_long_sub(i, &num_poisoned_pages);
+}
+
 #else
 
 static inline swp_entry_t make_hwpoison_entry(struct page *page)
@@ -518,6 +523,10 @@ static inline struct page *hwpoison_entry_to_page(swp_entry_t entry)
 static inline void num_poisoned_pages_inc(void)
 {
 }
+
+static inline void num_poisoned_pages_sub(long i)
+{
+}
 #endif
 
 static inline int non_swap_entry(swp_entry_t entry)
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 74195c181d69..56fd9d809013 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1720,21 +1720,38 @@ static int hugetlb_set_page_hwpoison(struct page *hpage, struct page *page)
 	return ret;
 }
 
-void hugetlb_clear_page_hwpoison(struct page *hpage)
+static unsigned long free_raw_hwp_pages(struct page *hpage, bool move_flag)
 {
 	struct llist_head *head;
 	struct llist_node *t, *tnode;
+	unsigned long count = 0;
 
-	if (!HPageRawHwpUnreliable(hpage))
-		ClearPageHWPoison(hpage);
+	/*
+	 * HPageVmemmapOptimized hugepages can't be unpoisoned because
+	 * struct pages for tail pages are required to free hwpoisoned
+	 * hugepages.  HPageRawHwpUnreliable hugepages shouldn't be
+	 * unpoisoned by definition.
+	 */
+	if (HPageVmemmapOptimized(hpage) || HPageRawHwpUnreliable(hpage))
+		return 0;
 	head = raw_hwp_list_head(hpage);
 	llist_for_each_safe(tnode, t, head->first) {
 		struct raw_hwp_page *p = container_of(tnode, struct raw_hwp_page, node);
 
-		SetPageHWPoison(p->page);
+		if (move_flag)
+			SetPageHWPoison(p->page);
 		kfree(p);
+		count++;
 	}
 	llist_del_all(head);
+	return count;
+}
+
+void hugetlb_clear_page_hwpoison(struct page *hpage)
+{
+	if (!HPageRawHwpUnreliable(hpage))
+		ClearPageHWPoison(hpage);
+	free_raw_hwp_pages(hpage, true);
 }
 
 /*
@@ -1878,6 +1895,10 @@ static inline int try_memory_failure_hugetlb(unsigned long pfn, int flags, int *
 	return 0;
 }
 
+static inline unsigned long free_raw_hwp_pages(struct page *hpage, bool flag)
+{
+	return 0;
+}
 #endif	/* CONFIG_HUGETLB_PAGE */
 
 static int memory_failure_dev_pagemap(unsigned long pfn, int flags,
@@ -2283,6 +2304,7 @@ int unpoison_memory(unsigned long pfn)
 	struct page *p;
 	int ret = -EBUSY;
 	int freeit = 0;
+	unsigned long count = 1;
 	static DEFINE_RATELIMIT_STATE(unpoison_rs, DEFAULT_RATELIMIT_INTERVAL,
 					DEFAULT_RATELIMIT_BURST);
 
@@ -2330,6 +2352,13 @@ int unpoison_memory(unsigned long pfn)
 
 	ret = get_hwpoison_page(p, MF_UNPOISON);
 	if (!ret) {
+		if (PageHuge(p)) {
+			count = free_raw_hwp_pages(page, false);
+			if (count == 0) {
+				ret = -EBUSY;
+				goto unlock_mutex;
+			}
+		}
 		ret = TestClearPageHWPoison(page) ? 0 : -EBUSY;
 	} else if (ret < 0) {
 		if (ret == -EHWPOISON) {
@@ -2338,6 +2367,13 @@ int unpoison_memory(unsigned long pfn)
 			unpoison_pr_info("Unpoison: failed to grab page %#lx\n",
 					 pfn, &unpoison_rs);
 	} else {
+		if (PageHuge(p)) {
+			count = free_raw_hwp_pages(page, false);
+			if (count == 0) {
+				ret = -EBUSY;
+				goto unlock_mutex;
+			}
+		}
 		freeit = !!TestClearPageHWPoison(p);
 
 		put_page(page);
@@ -2350,7 +2386,7 @@ int unpoison_memory(unsigned long pfn)
 unlock_mutex:
 	mutex_unlock(&mf_mutex);
 	if (!ret || freeit) {
-		num_poisoned_pages_dec();
+		num_poisoned_pages_sub(count);
 		unpoison_pr_info("Unpoison: Software-unpoisoned page %#lx\n",
 				 page_to_pfn(p), &unpoison_rs);
 	}
-- 
2.25.1

[mm-unstable PATCH v6 5/8] mm, hwpoison: set PG_hwpoison for busy hugetlb pages

[Naoya Horiguchi]

From: Naoya Horiguchi <naoya.horiguchi@nec.com>

If memory_failure() fails to grab page refcount on a hugetlb page
because it's busy, it returns without setting PG_hwpoison on it.
This not only loses a chance of error containment, but breaks the rule
that action_result() should be called only when memory_failure() do
any of handling work (even if that's just setting PG_hwpoison).
This inconsistency could harm code maintainability.

So set PG_hwpoison and call hugetlb_set_page_hwpoison() for such a case.

Fixes: 405ce051236c ("mm/hwpoison: fix race between hugetlb free/demotion and memory_failure_hugetlb()")
Signed-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
---
 include/linux/mm.h  | 1 +
 mm/memory-failure.c | 8 ++++----
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 4287bec50c28..7668831c919f 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -3188,6 +3188,7 @@ enum mf_flags {
 	MF_SOFT_OFFLINE = 1 << 3,
 	MF_UNPOISON = 1 << 4,
 	MF_SW_SIMULATED = 1 << 5,
+	MF_NO_RETRY = 1 << 6,
 };
 int mf_dax_kill_procs(struct address_space *mapping, pgoff_t index,
 		      unsigned long count, int mf_flags);
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 56fd9d809013..e90a685e326b 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1785,7 +1785,8 @@ int __get_huge_page_for_hwpoison(unsigned long pfn, int flags)
 			count_increased = true;
 	} else {
 		ret = -EBUSY;
-		goto out;
+		if (!(flags & MF_NO_RETRY))
+			goto out;
 	}
 
 	if (hugetlb_set_page_hwpoison(head, page)) {
@@ -1812,7 +1813,6 @@ static int try_memory_failure_hugetlb(unsigned long pfn, int flags, int *hugetlb
 	struct page *p = pfn_to_page(pfn);
 	struct page *head;
 	unsigned long page_flags;
-	bool retry = true;
 
 	*hugetlb = 1;
 retry:
@@ -1828,8 +1828,8 @@ static int try_memory_failure_hugetlb(unsigned long pfn, int flags, int *hugetlb
 		}
 		return res;
 	} else if (res == -EBUSY) {
-		if (retry) {
-			retry = false;
+		if (!(flags & MF_NO_RETRY)) {
+			flags |= MF_NO_RETRY;
 			goto retry;
 		}
 		action_result(pfn, MF_MSG_UNKNOWN, MF_IGNORED);
-- 
2.25.1

[mm-unstable PATCH v6 6/8] mm, hwpoison: make __page_handle_poison returns int

[Naoya Horiguchi]

From: Naoya Horiguchi <naoya.horiguchi@nec.com>

__page_handle_poison() returns bool that shows whether
take_page_off_buddy() has passed or not now.  But we will want to
distinguish another case of "dissolve has passed but taking off failed"
by its return value. So change the type of the return value.
No functional change.

Signed-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
---
v2 -> v3:
- move deleting "res = MF_FAILED" to the later patch. (by Miaohe)
---
 mm/memory-failure.c | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index e90a685e326b..390cb7df2f4a 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -71,7 +71,13 @@ atomic_long_t num_poisoned_pages __read_mostly = ATOMIC_LONG_INIT(0);
 
 static bool hw_memory_failure __read_mostly = false;
 
-static bool __page_handle_poison(struct page *page)
+/*
+ * Return values:
+ *   1:   the page is dissolved (if needed) and taken off from buddy,
+ *   0:   the page is dissolved (if needed) and not taken off from buddy,
+ *   < 0: failed to dissolve.
+ */
+static int __page_handle_poison(struct page *page)
 {
 	int ret;
 
@@ -81,7 +87,7 @@ static bool __page_handle_poison(struct page *page)
 		ret = take_page_off_buddy(page);
 	zone_pcp_enable(page_zone(page));
 
-	return ret > 0;
+	return ret;
 }
 
 static bool page_handle_poison(struct page *page, bool hugepage_or_freepage, bool release)
@@ -91,7 +97,7 @@ static bool page_handle_poison(struct page *page, bool hugepage_or_freepage, boo
 		 * Doing this check for free pages is also fine since dissolve_free_huge_page
 		 * returns 0 for non-hugetlb pages as well.
 		 */
-		if (!__page_handle_poison(page))
+		if (__page_handle_poison(page) <= 0)
 			/*
 			 * We could fail to take off the target page from buddy
 			 * for example due to racy page allocation, but that's
@@ -1086,7 +1092,7 @@ static int me_huge_page(struct page_state *ps, struct page *p)
 		 * subpages.
 		 */
 		put_page(hpage);
-		if (__page_handle_poison(p)) {
+		if (__page_handle_poison(p) > 0) {
 			page_ref_inc(p);
 			res = MF_RECOVERED;
 		}
@@ -1852,7 +1858,7 @@ static int try_memory_failure_hugetlb(unsigned long pfn, int flags, int *hugetlb
 	if (res == 0) {
 		unlock_page(head);
 		res = MF_FAILED;
-		if (__page_handle_poison(p)) {
+		if (__page_handle_poison(p) > 0) {
 			page_ref_inc(p);
 			res = MF_RECOVERED;
 		}
-- 
2.25.1

[mm-unstable PATCH v6 7/8] mm, hwpoison: skip raw hwpoison page in freeing 1GB hugepage

[Naoya Horiguchi]

From: Naoya Horiguchi <naoya.horiguchi@nec.com>

Currently if memory_failure() (modified to remove blocking code with
subsequent patch) is called on a page in some 1GB hugepage, memory error
handling fails and the raw error page gets into leaked state.  The impact
is small in production systems (just leaked single 4kB page), but this
limits the testability because unpoison doesn't work for it.
We can no longer create 1GB hugepage on the 1GB physical address range
with such leaked pages, that's not useful when testing on small systems.

When a hwpoison page in a 1GB hugepage is handled, it's caught by the
PageHWPoison check in free_pages_prepare() because the 1GB hugepage is
broken down into raw error pages before coming to this point:

        if (unlikely(PageHWPoison(page)) && !order) {
                ...
                return false;
        }

Then, the page is not sent to buddy and the page refcount is left 0.

Originally this check is supposed to work when the error page is freed from
page_handle_poison() (that is called from soft-offline), but now we are
opening another path to call it, so the callers of __page_handle_poison()
need to handle the case by considering the return value 0 as success. Then
page refcount for hwpoison is properly incremented so unpoison works.

Signed-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
---
v2 -> v3:
- remove "res = MF_FAILED" in try_memory_failure_hugetlb (by Miaohe)
---
 mm/memory-failure.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 390cb7df2f4a..a8be69f81aa0 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1084,7 +1084,6 @@ static int me_huge_page(struct page_state *ps, struct page *p)
 		res = truncate_error_page(hpage, page_to_pfn(p), mapping);
 		unlock_page(hpage);
 	} else {
-		res = MF_FAILED;
 		unlock_page(hpage);
 		/*
 		 * migration entry prevents later access on error hugepage,
@@ -1092,9 +1091,11 @@ static int me_huge_page(struct page_state *ps, struct page *p)
 		 * subpages.
 		 */
 		put_page(hpage);
-		if (__page_handle_poison(p) > 0) {
+		if (__page_handle_poison(p) >= 0) {
 			page_ref_inc(p);
 			res = MF_RECOVERED;
+		} else {
+			res = MF_FAILED;
 		}
 	}
 
@@ -1857,10 +1858,11 @@ static int try_memory_failure_hugetlb(unsigned long pfn, int flags, int *hugetlb
 	 */
 	if (res == 0) {
 		unlock_page(head);
-		res = MF_FAILED;
-		if (__page_handle_poison(p) > 0) {
+		if (__page_handle_poison(p) >= 0) {
 			page_ref_inc(p);
 			res = MF_RECOVERED;
+		} else {
+			res = MF_FAILED;
 		}
 		action_result(pfn, MF_MSG_FREE_HUGE, res);
 		return res == MF_RECOVERED ? 0 : -EBUSY;
-- 
2.25.1

[mm-unstable PATCH v6 8/8] mm, hwpoison: enable memory error handling on 1GB hugepage

[Naoya Horiguchi]

From: Naoya Horiguchi <naoya.horiguchi@nec.com>

Now error handling code is prepared, so remove the blocking code and
enable memory error handling on 1GB hugepage.

Signed-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
---
 include/linux/mm.h      |  1 -
 include/ras/ras_event.h |  1 -
 mm/memory-failure.c     | 16 ----------------
 3 files changed, 18 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 7668831c919f..b0e83835184e 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -3241,7 +3241,6 @@ enum mf_action_page_type {
 	MF_MSG_DIFFERENT_COMPOUND,
 	MF_MSG_HUGE,
 	MF_MSG_FREE_HUGE,
-	MF_MSG_NON_PMD_HUGE,
 	MF_MSG_UNMAP_FAILED,
 	MF_MSG_DIRTY_SWAPCACHE,
 	MF_MSG_CLEAN_SWAPCACHE,
diff --git a/include/ras/ras_event.h b/include/ras/ras_event.h
index d0337a41141c..cbd3ddd7c33d 100644
--- a/include/ras/ras_event.h
+++ b/include/ras/ras_event.h
@@ -360,7 +360,6 @@ TRACE_EVENT(aer_event,
 	EM ( MF_MSG_DIFFERENT_COMPOUND, "different compound page after locking" ) \
 	EM ( MF_MSG_HUGE, "huge page" )					\
 	EM ( MF_MSG_FREE_HUGE, "free huge page" )			\
-	EM ( MF_MSG_NON_PMD_HUGE, "non-pmd-sized huge page" )		\
 	EM ( MF_MSG_UNMAP_FAILED, "unmapping failed page" )		\
 	EM ( MF_MSG_DIRTY_SWAPCACHE, "dirty swapcache page" )		\
 	EM ( MF_MSG_CLEAN_SWAPCACHE, "clean swapcache page" )		\
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index a8be69f81aa0..2d58f1f9a538 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -765,7 +765,6 @@ static const char * const action_page_types[] = {
 	[MF_MSG_DIFFERENT_COMPOUND]	= "different compound page after locking",
 	[MF_MSG_HUGE]			= "huge page",
 	[MF_MSG_FREE_HUGE]		= "free huge page",
-	[MF_MSG_NON_PMD_HUGE]		= "non-pmd-sized huge page",
 	[MF_MSG_UNMAP_FAILED]		= "unmapping failed page",
 	[MF_MSG_DIRTY_SWAPCACHE]	= "dirty swapcache page",
 	[MF_MSG_CLEAN_SWAPCACHE]	= "clean swapcache page",
@@ -1870,21 +1869,6 @@ static int try_memory_failure_hugetlb(unsigned long pfn, int flags, int *hugetlb
 
 	page_flags = head->flags;
 
-	/*
-	 * TODO: hwpoison for pud-sized hugetlb doesn't work right now, so
-	 * simply disable it. In order to make it work properly, we need
-	 * make sure that:
-	 *  - conversion of a pud that maps an error hugetlb into hwpoison
-	 *    entry properly works, and
-	 *  - other mm code walking over page table is aware of pud-aligned
-	 *    hwpoison entries.
-	 */
-	if (huge_page_size(page_hstate(head)) > PMD_SIZE) {
-		action_result(pfn, MF_MSG_NON_PMD_HUGE, MF_IGNORED);
-		res = -EBUSY;
-		goto out;
-	}
-
 	if (!hwpoison_user_mappings(p, pfn, flags, head)) {
 		action_result(pfn, MF_MSG_UNMAP_FAILED, MF_IGNORED);
 		res = -EBUSY;
-- 
2.25.1

Re: [mm-unstable PATCH v6 4/8] mm, hwpoison: make unpoison aware of raw error info in hwpoisoned hugepage

[Miaohe Lin]

On 2022/7/12 11:28, Naoya Horiguchi wrote:
> From: Naoya Horiguchi <naoya.horiguchi@nec.com>
> 
> Raw error info list needs to be removed when hwpoisoned hugetlb is
> unpoisoned.  And unpoison handler needs to know how many errors there
> are in the target hugepage. So add them.
> 
> HPageVmemmapOptimized(hpage) and HPageRawHwpUnreliable(hpage)) can't be
> unpoisoned, so let's skip them.
> 
> Signed-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
> Reported-by: kernel test robot <lkp@intel.com>

This patch looks good to me with some nits below.

> ---
...
>  
> -void hugetlb_clear_page_hwpoison(struct page *hpage)
> +static unsigned long free_raw_hwp_pages(struct page *hpage, bool move_flag)
>  {
>  	struct llist_head *head;
>  	struct llist_node *t, *tnode;
> +	unsigned long count = 0;
>  
> -	if (!HPageRawHwpUnreliable(hpage))
> -		ClearPageHWPoison(hpage);
> +	/*
> +	 * HPageVmemmapOptimized hugepages can't be unpoisoned because
> +	 * struct pages for tail pages are required to free hwpoisoned
> +	 * hugepages.  HPageRawHwpUnreliable hugepages shouldn't be
> +	 * unpoisoned by definition.
> +	 */
> +	if (HPageVmemmapOptimized(hpage) || HPageRawHwpUnreliable(hpage))

If move_flag == false, i.e. in unpoison case, tail pages are not touched. So HPageVmemmapOptimized
can be ignored in this case? Or leave it as above to keep the code simple?

> +		return 0;
>  	head = raw_hwp_list_head(hpage);
>  	llist_for_each_safe(tnode, t, head->first) {
>  		struct raw_hwp_page *p = container_of(tnode, struct raw_hwp_page, node);
>  
> -		SetPageHWPoison(p->page);
> +		if (move_flag)
> +			SetPageHWPoison(p->page);
>  		kfree(p);
> +		count++;
>  	}
>  	llist_del_all(head);
> +	return count;
> +}
> +
> +void hugetlb_clear_page_hwpoison(struct page *hpage)
> +{
> +	if (!HPageRawHwpUnreliable(hpage))

It seems we can return here if HPageRawHwpUnreliable as there's nothing to do?

Anyway, for what it worth,

Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>

Thanks.

> +		ClearPageHWPoison(hpage);
> +	free_raw_hwp_pages(hpage, true);
>  }
>  
>  /*

Re: [mm-unstable PATCH v6 3/8] mm, hwpoison, hugetlb: support saving mechanism of raw error pages

[Miaohe Lin]

On 2022/7/12 11:28, Naoya Horiguchi wrote:
> From: Naoya Horiguchi <naoya.horiguchi@nec.com>
> 
> When handling memory error on a hugetlb page, the error handler tries to
> dissolve and turn it into 4kB pages.  If it's successfully dissolved,
> PageHWPoison flag is moved to the raw error page, so that's all right.
> However, dissolve sometimes fails, then the error page is left as
> hwpoisoned hugepage. It's useful if we can retry to dissolve it to save
> healthy pages, but that's not possible now because the information about
> where the raw error pages is lost.
> 
> Use the private field of a few tail pages to keep that information.  The
> code path of shrinking hugepage pool uses this info to try delayed dissolve.
> In order to remember multiple errors in a hugepage, a singly-linked list
> originated from SUBPAGE_INDEX_HWPOISON-th tail page is constructed.  Only
> simple operations (adding an entry or clearing all) are required and the
> list is assumed not to be very long, so this simple data structure should
> be enough.
> 
> If we failed to save raw error info, the hwpoison hugepage has errors on
> unknown subpage, then this new saving mechanism does not work any more,
> so disable saving new raw error info and freeing hwpoison hugepages.
> 
> Signed-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
> Reported-by: kernel test robot <lkp@intel.com>

This patch looks good to me with some nits below.

> ---
...
> +static int hugetlb_set_page_hwpoison(struct page *hpage, struct page *page)
> +{
> +	struct llist_head *head;
> +	struct raw_hwp_page *raw_hwp;
> +	struct llist_node *t, *tnode;
> +	int ret = TestSetPageHWPoison(hpage) ? -EHWPOISON : 0;
> +
> +	/*
> +	 * Once the hwpoison hugepage has lost reliable raw error info,
> +	 * there is little meaning to keep additional error info precisely,
> +	 * so skip to add additional raw error info.
> +	 */
> +	if (HPageRawHwpUnreliable(hpage))
> +		return -EHWPOISON;
> +	head = raw_hwp_list_head(hpage);
> +	llist_for_each_safe(tnode, t, head->first) {
> +		struct raw_hwp_page *p = container_of(tnode, struct raw_hwp_page, node);
> +
> +		if (p->page == page)
> +			return -EHWPOISON;
> +	}
> +
> +	raw_hwp = kmalloc(sizeof(struct raw_hwp_page), GFP_ATOMIC);
> +	if (raw_hwp) {
> +		raw_hwp->page = page;
> +		llist_add(&raw_hwp->node, head);
> +		/* the first error event will be counted in action_result(). */
> +		if (ret)
> +			num_poisoned_pages_inc();
> +	} else {
> +		/*
> +		 * Failed to save raw error info.  We no longer trace all
> +		 * hwpoisoned subpages, and we need refuse to free/dissolve
> +		 * this hwpoisoned hugepage.
> +		 */
> +		SetHPageRawHwpUnreliable(hpage);

IMHO, when HPageRawHwpUnreliable is set, we can simply free the raw_hwp_list here
to save some memory as they're not used anymore.

> +	}
> +	return ret;
> +}
> +
> +void hugetlb_clear_page_hwpoison(struct page *hpage)
> +{
> +	struct llist_head *head;
> +	struct llist_node *t, *tnode;
> +
> +	if (!HPageRawHwpUnreliable(hpage))
> +		ClearPageHWPoison(hpage);
> +	head = raw_hwp_list_head(hpage);
> +	llist_for_each_safe(tnode, t, head->first) {
> +		struct raw_hwp_page *p = container_of(tnode, struct raw_hwp_page, node);
> +
> +		SetPageHWPoison(p->page);
> +		kfree(p);
> +	}
> +	llist_del_all(head);
> +}
> +
>  /*
>   * Called from hugetlb code with hugetlb_lock held.
>   *
> @@ -1698,7 +1771,7 @@ int __get_huge_page_for_hwpoison(unsigned long pfn, int flags)
>  		goto out;
>  	}
>  
> -	if (TestSetPageHWPoison(head)) {
> +	if (hugetlb_set_page_hwpoison(head, page)) {
>  		ret = -EHWPOISON;
>  		goto out;
>  	}
> @@ -1710,7 +1783,6 @@ int __get_huge_page_for_hwpoison(unsigned long pfn, int flags)
>  	return ret;
>  }
>  
> -#ifdef CONFIG_HUGETLB_PAGE
>  /*
>   * Taking refcount of hugetlb pages needs extra care about race conditions
>   * with basic operations like hugepage allocation/free/demotion.
> @@ -1751,7 +1823,7 @@ static int try_memory_failure_hugetlb(unsigned long pfn, int flags, int *hugetlb
>  	lock_page(head);
>  
>  	if (hwpoison_filter(p)) {
> -		ClearPageHWPoison(head);
> +		hugetlb_clear_page_hwpoison(head);

If the code reach here, the hugetlb page should be poisoned first time or it will return
in above "res == -EHWPOISON" case. So ClearPageHWPoison should be fine here. But this change
will do the same thing while making the code more consistent. So it should be fine. :)

>  		res = -EOPNOTSUPP;
>  		goto out;
>  	}
> 

Anyway, for what it worth,

Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>

Thanks!

Re: [mm-unstable PATCH v6 4/8] mm, hwpoison: make unpoison aware of raw error info in hwpoisoned hugepage

[HORIGUCHI NAOYA(堀口 直也)]

On Wed, Jul 13, 2022 at 12:24:46PM +0800, Miaohe Lin wrote:
> On 2022/7/12 11:28, Naoya Horiguchi wrote:
> > From: Naoya Horiguchi <naoya.horiguchi@nec.com>
> > 
> > Raw error info list needs to be removed when hwpoisoned hugetlb is
> > unpoisoned.  And unpoison handler needs to know how many errors there
> > are in the target hugepage. So add them.
> > 
> > HPageVmemmapOptimized(hpage) and HPageRawHwpUnreliable(hpage)) can't be
> > unpoisoned, so let's skip them.
> > 
> > Signed-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
> > Reported-by: kernel test robot <lkp@intel.com>
> 
> This patch looks good to me with some nits below.
> 
> > ---
> ...
> >  
> > -void hugetlb_clear_page_hwpoison(struct page *hpage)
> > +static unsigned long free_raw_hwp_pages(struct page *hpage, bool move_flag)
> >  {
> >  	struct llist_head *head;
> >  	struct llist_node *t, *tnode;
> > +	unsigned long count = 0;
> >  
> > -	if (!HPageRawHwpUnreliable(hpage))
> > -		ClearPageHWPoison(hpage);
> > +	/*
> > +	 * HPageVmemmapOptimized hugepages can't be unpoisoned because
> > +	 * struct pages for tail pages are required to free hwpoisoned
> > +	 * hugepages.  HPageRawHwpUnreliable hugepages shouldn't be
> > +	 * unpoisoned by definition.
> > +	 */
> > +	if (HPageVmemmapOptimized(hpage) || HPageRawHwpUnreliable(hpage))
> 
> If move_flag == false, i.e. in unpoison case, tail pages are not touched. So HPageVmemmapOptimized
> can be ignored in this case? Or leave it as above to keep the code simple?

Oh, right.  We can make HPageVmemmapOptimized() more conditional.

> 
> > +		return 0;
> >  	head = raw_hwp_list_head(hpage);
> >  	llist_for_each_safe(tnode, t, head->first) {
> >  		struct raw_hwp_page *p = container_of(tnode, struct raw_hwp_page, node);
> >  
> > -		SetPageHWPoison(p->page);
> > +		if (move_flag)
> > +			SetPageHWPoison(p->page);
> >  		kfree(p);
> > +		count++;
> >  	}
> >  	llist_del_all(head);
> > +	return count;
> > +}
> > +
> > +void hugetlb_clear_page_hwpoison(struct page *hpage)
> > +{
> > +	if (!HPageRawHwpUnreliable(hpage))
> 
> It seems we can return here if HPageRawHwpUnreliable as there's nothing to do?

OK, I'll update this, too.

> 
> Anyway, for what it worth,
> 
> Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>

Thank you.
- Naoya Horiguchi

> 
> Thanks.
> 
> > +		ClearPageHWPoison(hpage);
> > +	free_raw_hwp_pages(hpage, true);
> >  }
> >  
> >  /*

Re: [mm-unstable PATCH v6 3/8] mm, hwpoison, hugetlb: support saving mechanism of raw error pages

[HORIGUCHI NAOYA(堀口 直也)]

On Wed, Jul 13, 2022 at 12:51:30PM +0800, Miaohe Lin wrote:
> On 2022/7/12 11:28, Naoya Horiguchi wrote:
> > From: Naoya Horiguchi <naoya.horiguchi@nec.com>
> > 
> > When handling memory error on a hugetlb page, the error handler tries to
> > dissolve and turn it into 4kB pages.  If it's successfully dissolved,
> > PageHWPoison flag is moved to the raw error page, so that's all right.
> > However, dissolve sometimes fails, then the error page is left as
> > hwpoisoned hugepage. It's useful if we can retry to dissolve it to save
> > healthy pages, but that's not possible now because the information about
> > where the raw error pages is lost.
> > 
> > Use the private field of a few tail pages to keep that information.  The
> > code path of shrinking hugepage pool uses this info to try delayed dissolve.
> > In order to remember multiple errors in a hugepage, a singly-linked list
> > originated from SUBPAGE_INDEX_HWPOISON-th tail page is constructed.  Only
> > simple operations (adding an entry or clearing all) are required and the
> > list is assumed not to be very long, so this simple data structure should
> > be enough.
> > 
> > If we failed to save raw error info, the hwpoison hugepage has errors on
> > unknown subpage, then this new saving mechanism does not work any more,
> > so disable saving new raw error info and freeing hwpoison hugepages.
> > 
> > Signed-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
> > Reported-by: kernel test robot <lkp@intel.com>
> 
> This patch looks good to me with some nits below.
> 
> > ---
> ...
> > +static int hugetlb_set_page_hwpoison(struct page *hpage, struct page *page)
> > +{
> > +	struct llist_head *head;
> > +	struct raw_hwp_page *raw_hwp;
> > +	struct llist_node *t, *tnode;
> > +	int ret = TestSetPageHWPoison(hpage) ? -EHWPOISON : 0;
> > +
> > +	/*
> > +	 * Once the hwpoison hugepage has lost reliable raw error info,
> > +	 * there is little meaning to keep additional error info precisely,
> > +	 * so skip to add additional raw error info.
> > +	 */
> > +	if (HPageRawHwpUnreliable(hpage))
> > +		return -EHWPOISON;
> > +	head = raw_hwp_list_head(hpage);
> > +	llist_for_each_safe(tnode, t, head->first) {
> > +		struct raw_hwp_page *p = container_of(tnode, struct raw_hwp_page, node);
> > +
> > +		if (p->page == page)
> > +			return -EHWPOISON;
> > +	}
> > +
> > +	raw_hwp = kmalloc(sizeof(struct raw_hwp_page), GFP_ATOMIC);
> > +	if (raw_hwp) {
> > +		raw_hwp->page = page;
> > +		llist_add(&raw_hwp->node, head);
> > +		/* the first error event will be counted in action_result(). */
> > +		if (ret)
> > +			num_poisoned_pages_inc();
> > +	} else {
> > +		/*
> > +		 * Failed to save raw error info.  We no longer trace all
> > +		 * hwpoisoned subpages, and we need refuse to free/dissolve
> > +		 * this hwpoisoned hugepage.
> > +		 */
> > +		SetHPageRawHwpUnreliable(hpage);
> 
> IMHO, when HPageRawHwpUnreliable is set, we can simply free the raw_hwp_list here
> to save some memory as they're not used anymore.

Yes, that's possible. Let's do this.

> 
> > +	}
> > +	return ret;
> > +}
> > +
> > +void hugetlb_clear_page_hwpoison(struct page *hpage)
> > +{
> > +	struct llist_head *head;
> > +	struct llist_node *t, *tnode;
> > +
> > +	if (!HPageRawHwpUnreliable(hpage))
> > +		ClearPageHWPoison(hpage);
> > +	head = raw_hwp_list_head(hpage);
> > +	llist_for_each_safe(tnode, t, head->first) {
> > +		struct raw_hwp_page *p = container_of(tnode, struct raw_hwp_page, node);
> > +
> > +		SetPageHWPoison(p->page);
> > +		kfree(p);
> > +	}
> > +	llist_del_all(head);
> > +}
> > +
> >  /*
> >   * Called from hugetlb code with hugetlb_lock held.
> >   *
> > @@ -1698,7 +1771,7 @@ int __get_huge_page_for_hwpoison(unsigned long pfn, int flags)
> >  		goto out;
> >  	}
> >  
> > -	if (TestSetPageHWPoison(head)) {
> > +	if (hugetlb_set_page_hwpoison(head, page)) {
> >  		ret = -EHWPOISON;
> >  		goto out;
> >  	}
> > @@ -1710,7 +1783,6 @@ int __get_huge_page_for_hwpoison(unsigned long pfn, int flags)
> >  	return ret;
> >  }
> >  
> > -#ifdef CONFIG_HUGETLB_PAGE
> >  /*
> >   * Taking refcount of hugetlb pages needs extra care about race conditions
> >   * with basic operations like hugepage allocation/free/demotion.
> > @@ -1751,7 +1823,7 @@ static int try_memory_failure_hugetlb(unsigned long pfn, int flags, int *hugetlb
> >  	lock_page(head);
> >  
> >  	if (hwpoison_filter(p)) {
> > -		ClearPageHWPoison(head);
> > +		hugetlb_clear_page_hwpoison(head);
> 
> If the code reach here, the hugetlb page should be poisoned first time or it will return
> in above "res == -EHWPOISON" case. So ClearPageHWPoison should be fine here. But this change
> will do the same thing while making the code more consistent. So it should be fine. :)

Right, this change is for consistency.

> 
> >  		res = -EOPNOTSUPP;
> >  		goto out;
> >  	}
> > 
> 
> Anyway, for what it worth,
> 
> Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
> 
> Thanks!

Thank you.
- Naoya Horiguchi