From: Naoya Horiguchi <[email protected]>
__get_hwpoison_page() could fail to grab refcount by some race
condition, so it's helpful if we can handle it by retrying.
We already have retry logic, so make get_hwpoison_page() call
get_any_page() when called from memory_failure().
Signed-off-by: Naoya Horiguchi <[email protected]>
---
ChangeLog v4:
- __get_hwpoison_page() returns -EBUSY (not in the previous patch),
- moved "if (ret == -EBUSY)" block,
- improved comment.
---
mm/memory-failure.c | 114 ++++++++++++++++++++++++--------------------
1 file changed, 63 insertions(+), 51 deletions(-)
diff --git v5.12/mm/memory-failure.c v5.12_patched/mm/memory-failure.c
index 761f982b6d7b..85275972cc6f 100644
--- v5.12/mm/memory-failure.c
+++ v5.12_patched/mm/memory-failure.c
@@ -1084,13 +1084,6 @@ static int page_action(struct page_state *ps, struct page *p,
return (result == MF_RECOVERED || result == MF_DELAYED) ? 0 : -EBUSY;
}
-/**
- * __get_hwpoison_page() - Get refcount for memory error handling:
- * @page: raw error page (hit by memory error)
- *
- * Return: return 0 if failed to grab the refcount, otherwise true (some
- * non-zero value.)
- */
static int __get_hwpoison_page(struct page *page)
{
struct page *head = compound_head(page);
@@ -1098,7 +1091,9 @@ static int __get_hwpoison_page(struct page *page)
#ifdef CONFIG_HUGETLB_PAGE
spin_lock(&hugetlb_lock);
- if (PageHuge(head) && (HPageFreed(head) || HPageMigratable(head)))
+ if (!PageHuge(head))
+ ret = -EBUSY;
+ else if (HPageFreed(head) || HPageMigratable(head))
ret = get_page_unless_zero(head);
spin_unlock(&hugetlb_lock);
if (ret > 0)
@@ -1131,15 +1126,6 @@ static int __get_hwpoison_page(struct page *page)
return 0;
}
-/*
- * Safely get reference count of an arbitrary page.
- *
- * Returns 0 for a free page, 1 for an in-use page,
- * -EIO for a page-type we cannot handle and -EBUSY if we raced with an
- * allocation.
- * We only incremented refcount in case the page was already in-use and it
- * is a known type we can handle.
- */
static int get_any_page(struct page *p, unsigned long flags)
{
int ret = 0, pass = 0;
@@ -1149,50 +1135,76 @@ static int get_any_page(struct page *p, unsigned long flags)
count_increased = true;
try_again:
- if (!count_increased && !__get_hwpoison_page(p)) {
- if (page_count(p)) {
- /* We raced with an allocation, retry. */
- if (pass++ < 3)
- goto try_again;
- ret = -EBUSY;
- } else if (!PageHuge(p) && !is_free_buddy_page(p)) {
- /* We raced with put_page, retry. */
+ if (!count_increased) {
+ ret = __get_hwpoison_page(p);
+ if (!ret) {
+ if (page_count(p)) {
+ /* We raced with an allocation, retry. */
+ if (pass++ < 3)
+ goto try_again;
+ ret = -EBUSY;
+ } else if (!PageHuge(p) && !is_free_buddy_page(p)) {
+ /* We raced with put_page, retry. */
+ if (pass++ < 3)
+ goto try_again;
+ ret = -EIO;
+ }
+ goto out;
+ } else if (ret == -EBUSY) {
+ /* We raced with freeing huge page to buddy, retry. */
if (pass++ < 3)
goto try_again;
- ret = -EIO;
}
+ }
+
+ if (PageHuge(p) || PageLRU(p) || __PageMovable(p)) {
+ ret = 1;
} else {
- if (PageHuge(p) || PageLRU(p) || __PageMovable(p)) {
- ret = 1;
- } else {
- /*
- * A page we cannot handle. Check whether we can turn
- * it into something we can handle.
- */
- if (pass++ < 3) {
- put_page(p);
- shake_page(p, 1);
- count_increased = false;
- goto try_again;
- }
+ /*
+ * A page we cannot handle. Check whether we can turn
+ * it into something we can handle.
+ */
+ if (pass++ < 3) {
put_page(p);
- ret = -EIO;
+ shake_page(p, 1);
+ count_increased = false;
+ goto try_again;
}
+ put_page(p);
+ ret = -EIO;
}
-
+out:
return ret;
}
-static int get_hwpoison_page(struct page *p, unsigned long flags,
- enum mf_flags ctxt)
+/**
+ * get_hwpoison_page() - Get refcount for memory error handling
+ * @p: Raw error page (hit by memory error)
+ * @flags: Flags controlling behavior of error handling
+ *
+ * get_hwpoison_page() takes a page refcount of an error page to handle memory
+ * error on it, after checking that the error page is in a well-defined state
+ * (defined as a page-type we can successfully handle the memor error on it,
+ * such as LRU page and hugetlb page).
+ *
+ * Memory error handling could be triggered at any time on any type of page,
+ * so it's prone to race with typical memory management lifecycle (like
+ * allocation and free). So to avoid such races, get_hwpoison_page() takes
+ * extra care for the error page's state (as done in __get_hwpoison_page()),
+ * and has some retry logic in get_any_page().
+ *
+ * Return: 0 on failure,
+ * 1 on success for in-use pages in a well-defined state,
+ * -EIO for pages on which we can not handle memory errors,
+ * -EBUSY when get_hwpoison_page() has raced with page lifecycle
+ * operations like allocation and free.
+ */
+static int get_hwpoison_page(struct page *p, unsigned long flags)
{
int ret;
zone_pcp_disable(page_zone(p));
- if (ctxt == MF_SOFT_OFFLINE)
- ret = get_any_page(p, flags);
- else
- ret = __get_hwpoison_page(p);
+ ret = get_any_page(p, flags);
zone_pcp_enable(page_zone(p));
return ret;
@@ -1381,7 +1393,7 @@ static int memory_failure_hugetlb(unsigned long pfn, int flags)
num_poisoned_pages_inc();
- if (!(flags & MF_COUNT_INCREASED) && !get_hwpoison_page(p, flags, 0)) {
+ if (!(flags & MF_COUNT_INCREASED) && !get_hwpoison_page(p, flags)) {
/*
* Check "filter hit" and "race with other subpage."
*/
@@ -1605,7 +1617,7 @@ int memory_failure(unsigned long pfn, int flags)
* In fact it's dangerous to directly bump up page count from 0,
* that may make page_ref_freeze()/page_ref_unfreeze() mismatch.
*/
- if (!(flags & MF_COUNT_INCREASED) && !get_hwpoison_page(p, flags, 0)) {
+ if (!(flags & MF_COUNT_INCREASED) && !get_hwpoison_page(p, flags)) {
if (is_free_buddy_page(p)) {
if (take_page_off_buddy(p)) {
page_ref_inc(p);
@@ -1897,7 +1909,7 @@ int unpoison_memory(unsigned long pfn)
return 0;
}
- if (!get_hwpoison_page(p, flags, 0)) {
+ if (!get_hwpoison_page(p, flags)) {
if (TestClearPageHWPoison(p))
num_poisoned_pages_dec();
unpoison_pr_info("Unpoison: Software-unpoisoned free page %#lx\n",
@@ -2113,7 +2125,7 @@ int soft_offline_page(unsigned long pfn, int flags)
retry:
get_online_mems();
- ret = get_hwpoison_page(page, flags, MF_SOFT_OFFLINE);
+ ret = get_hwpoison_page(page, flags);
put_online_mems();
if (ret > 0) {
--
2.25.1
On Mon, May 17, 2021 at 01:54:01PM +0900, Naoya Horiguchi wrote:
> static int __get_hwpoison_page(struct page *page)
> {
> struct page *head = compound_head(page);
> @@ -1098,7 +1091,9 @@ static int __get_hwpoison_page(struct page *page)
>
> #ifdef CONFIG_HUGETLB_PAGE
> spin_lock(&hugetlb_lock);
> - if (PageHuge(head) && (HPageFreed(head) || HPageMigratable(head)))
> + if (!PageHuge(head))
> + ret = -EBUSY;
Unless I'm missing something, we will be returning -EBUSY for any non-hugetlb
page, which is not right.
I think what you want is to return -EBUSY in case the page is a hugetlb page
but we cannot grab a refcount because the page is in a floating state, meaning
!HPageFreed && !HPageMigratable.
Right?
--
Oscar Salvador
SUSE L3
On Mon, May 17, 2021 at 02:59:03PM +0200, Oscar Salvador wrote:
> On Mon, May 17, 2021 at 01:54:01PM +0900, Naoya Horiguchi wrote:
> > static int __get_hwpoison_page(struct page *page)
> > {
> > struct page *head = compound_head(page);
> > @@ -1098,7 +1091,9 @@ static int __get_hwpoison_page(struct page *page)
> >
> > #ifdef CONFIG_HUGETLB_PAGE
> > spin_lock(&hugetlb_lock);
> > - if (PageHuge(head) && (HPageFreed(head) || HPageMigratable(head)))
> > + if (!PageHuge(head))
> > + ret = -EBUSY;
>
> Unless I'm missing something, we will be returning -EBUSY for any non-hugetlb
> page, which is not right.
(sigh, hard to say why I wrote this, really sorry)
> I think what you want is to return -EBUSY in case the page is a hugetlb page
> but we cannot grab a refcount because the page is in a floating state, meaning
> !HPageFreed && !HPageMigratable.
>
> Right?
Totally right, so the below should what's wanted.
spin_lock(&hugetlb_lock);
if (PageHuge(head))
if (!HPageFreed(head) && !HPageMigratable(head))
ret = -EBUSY;
else
ret = get_page_unless_zero(head);
spin_unlock(&hugetlb_lock);
- Naoya