[PATCH v1 2/2] mm: soft-offline: close the race against page allocation
From: Naoya Horiguchi
Date: Thu Jul 12 2018 - 23:26:49 EST
A process can be killed with SIGBUS(BUS_MCEERR_AR) when it tries to
allocate a page that was just freed on the way of soft-offline.
This is undesirable because soft-offline (which is about corrected error)
is less aggressive than hard-offline (which is about uncorrected error),
and we can make soft-offline fail and keep using the page for good reason
like "system is busy."
Two main changes of this patch are:
- setting migrate type of the target page to MIGRATE_ISOLATE. As done
in free_unref_page_commit(), this makes kernel bypass pcplist when
freeing the page. So we can assume that the page is in freelist just
after put_page() returns,
- setting PG_hwpoison on free page under zone->lock which protects
freelists, so this allows us to avoid setting PG_hwpoison on a page
that is decided to be allocated soon.
Reported-by: Xishi Qiu <xishi.qiuxishi@xxxxxxxxxxxxxxx>
Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
---
include/linux/page-flags.h | 5 +++++
include/linux/swapops.h | 10 ----------
mm/memory-failure.c | 26 +++++++++++++++++++++-----
mm/migrate.c | 2 +-
mm/page_alloc.c | 29 +++++++++++++++++++++++++++++
5 files changed, 56 insertions(+), 16 deletions(-)
diff --git v4.18-rc4-mmotm-2018-07-10-16-50/include/linux/page-flags.h v4.18-rc4-mmotm-2018-07-10-16-50_patched/include/linux/page-flags.h
index 901943e..74bee8c 100644
--- v4.18-rc4-mmotm-2018-07-10-16-50/include/linux/page-flags.h
+++ v4.18-rc4-mmotm-2018-07-10-16-50_patched/include/linux/page-flags.h
@@ -369,8 +369,13 @@ PAGEFLAG_FALSE(Uncached)
PAGEFLAG(HWPoison, hwpoison, PF_ANY)
TESTSCFLAG(HWPoison, hwpoison, PF_ANY)
#define __PG_HWPOISON (1UL << PG_hwpoison)
+extern bool set_hwpoison_free_buddy_page(struct page *page);
#else
PAGEFLAG_FALSE(HWPoison)
+static inline bool set_hwpoison_free_buddy_page(struct page *page)
+{
+ return 0;
+}
#define __PG_HWPOISON 0
#endif
diff --git v4.18-rc4-mmotm-2018-07-10-16-50/include/linux/swapops.h v4.18-rc4-mmotm-2018-07-10-16-50_patched/include/linux/swapops.h
index 9c0eb4d..fe8e08b 100644
--- v4.18-rc4-mmotm-2018-07-10-16-50/include/linux/swapops.h
+++ v4.18-rc4-mmotm-2018-07-10-16-50_patched/include/linux/swapops.h
@@ -335,11 +335,6 @@ static inline int is_hwpoison_entry(swp_entry_t entry)
return swp_type(entry) == SWP_HWPOISON;
}
-static inline bool test_set_page_hwpoison(struct page *page)
-{
- return TestSetPageHWPoison(page);
-}
-
static inline void num_poisoned_pages_inc(void)
{
atomic_long_inc(&num_poisoned_pages);
@@ -362,11 +357,6 @@ static inline int is_hwpoison_entry(swp_entry_t swp)
return 0;
}
-static inline bool test_set_page_hwpoison(struct page *page)
-{
- return false;
-}
-
static inline void num_poisoned_pages_inc(void)
{
}
diff --git v4.18-rc4-mmotm-2018-07-10-16-50/mm/memory-failure.c v4.18-rc4-mmotm-2018-07-10-16-50_patched/mm/memory-failure.c
index c63d982..794687a 100644
--- v4.18-rc4-mmotm-2018-07-10-16-50/mm/memory-failure.c
+++ v4.18-rc4-mmotm-2018-07-10-16-50_patched/mm/memory-failure.c
@@ -57,6 +57,7 @@
#include <linux/mm_inline.h>
#include <linux/kfifo.h>
#include <linux/ratelimit.h>
+#include <linux/page-isolation.h>
#include "internal.h"
#include "ras/ras_event.h"
@@ -1697,6 +1698,7 @@ static int __soft_offline_page(struct page *page, int flags)
static int soft_offline_in_use_page(struct page *page, int flags)
{
int ret;
+ int mt;
struct page *hpage = compound_head(page);
if (!PageHuge(page) && PageTransHuge(hpage)) {
@@ -1715,23 +1717,37 @@ static int soft_offline_in_use_page(struct page *page, int flags)
put_hwpoison_page(hpage);
}
+ /*
+ * Setting MIGRATE_ISOLATE here ensures that the page will be linked
+ * to free list immediately (not via pcplist) when released after
+ * successful page migration. Otherwise we can't guarantee that the
+ * page is really free after put_page() returns, so
+ * set_hwpoison_free_buddy_page() highly likely fails.
+ */
+ mt = get_pageblock_migratetype(page);
+ set_pageblock_migratetype(page, MIGRATE_ISOLATE);
if (PageHuge(page))
ret = soft_offline_huge_page(page, flags);
else
ret = __soft_offline_page(page, flags);
-
+ set_pageblock_migratetype(page, mt);
return ret;
}
-static void soft_offline_free_page(struct page *page)
+static int soft_offline_free_page(struct page *page)
{
int rc = 0;
struct page *head = compound_head(page);
if (PageHuge(head))
rc = dissolve_free_huge_page(page);
- if (!rc && !TestSetPageHWPoison(page))
- num_poisoned_pages_inc();
+ if (!rc) {
+ if (set_hwpoison_free_buddy_page(page))
+ num_poisoned_pages_inc();
+ else
+ rc = -EBUSY;
+ }
+ return rc;
}
/**
@@ -1775,7 +1791,7 @@ int soft_offline_page(struct page *page, int flags)
if (ret > 0)
ret = soft_offline_in_use_page(page, flags);
else if (ret == 0)
- soft_offline_free_page(page);
+ ret = soft_offline_free_page(page);
return ret;
}
diff --git v4.18-rc4-mmotm-2018-07-10-16-50/mm/migrate.c v4.18-rc4-mmotm-2018-07-10-16-50_patched/mm/migrate.c
index 3ae213b..e772323 100644
--- v4.18-rc4-mmotm-2018-07-10-16-50/mm/migrate.c
+++ v4.18-rc4-mmotm-2018-07-10-16-50_patched/mm/migrate.c
@@ -1199,7 +1199,7 @@ static ICE_noinline int unmap_and_move(new_page_t get_new_page,
* intentionally. Although it's rather weird,
* it's how HWPoison flag works at the moment.
*/
- if (!test_set_page_hwpoison(page))
+ if (set_hwpoison_free_buddy_page(page))
num_poisoned_pages_inc();
}
} else {
diff --git v4.18-rc4-mmotm-2018-07-10-16-50/mm/page_alloc.c v4.18-rc4-mmotm-2018-07-10-16-50_patched/mm/page_alloc.c
index 607deff..3c76d40 100644
--- v4.18-rc4-mmotm-2018-07-10-16-50/mm/page_alloc.c
+++ v4.18-rc4-mmotm-2018-07-10-16-50_patched/mm/page_alloc.c
@@ -8027,3 +8027,32 @@ bool is_free_buddy_page(struct page *page)
return order < MAX_ORDER;
}
+
+#ifdef CONFIG_MEMORY_FAILURE
+/*
+ * Set PG_hwpoison flag if a given page is confirmed to be a free page
+ * within zone lock, which prevents the race against page allocation.
+ */
+bool set_hwpoison_free_buddy_page(struct page *page)
+{
+ struct zone *zone = page_zone(page);
+ unsigned long pfn = page_to_pfn(page);
+ unsigned long flags;
+ unsigned int order;
+ bool hwpoisoned = false;
+
+ spin_lock_irqsave(&zone->lock, flags);
+ for (order = 0; order < MAX_ORDER; order++) {
+ struct page *page_head = page - (pfn & ((1 << order) - 1));
+
+ if (PageBuddy(page_head) && page_order(page_head) >= order) {
+ if (!TestSetPageHWPoison(page))
+ hwpoisoned = true;
+ break;
+ }
+ }
+ spin_unlock_irqrestore(&zone->lock, flags);
+
+ return hwpoisoned;
+}
+#endif
--
2.7.0