MCE: fix an error of mce_bad_pages statistics

On x86 platform, if we use "/sys/devices/system/memory/soft_offline_page" to offline a free page twice, the value of mce_bad_pages will be added twice. So this is an error, since the page was already marked HWPoison, we should skip the page and don't add the value of mce_bad_pages.

$ cat /proc/meminfo | grep HardwareCorrupted

soft_offline_page()

	get_any_page()
		atomic_long_add(1, &mce_bad_pages)

The free page which marked HWPoison is still managed by page buddy allocator. So when offlining it again, get_any_page() always returns 0 with
"pr_info("%s: %#lx free buddy page\n", __func__, pfn);".

When page is allocated, the PageBuddy is removed in bad_page(), then get_any_page() returns -EIO with pr_info("%s: %#lx: unknown zero refcount page type %lx\n", so mce_bad_pages will not be added.

Signed-off-by Xishi Qiu <[email protected]>

i>>?Signed-off-by: Jiang Liu <[email protected]>

---
 mm/memory-failure.c |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)

mm/memory-failure.c +0 -0

index 8b20278..02a522e 100644

Quoted 30 lines · Xishi Qiu

On x86 platform, if we use "/sys/devices/system/memory/soft_offline_page" to offline a free page twice, the value of mce_bad_pages will be added twice. So this is an error, since the page was already marked HWPoison, we should skip the page and don't add the value of mce_bad_pages.

$ cat /proc/meminfo | grep HardwareCorrupted

soft_offline_page()

	get_any_page()
		atomic_long_add(1, &mce_bad_pages)

The free page which marked HWPoison is still managed by page buddy allocator. So when offlining it again, get_any_page() always returns 0 with
"pr_info("%s: %#lx free buddy page\n", __func__, pfn);".

When page is allocated, the PageBuddy is removed in bad_page(), then get_any_page() returns -EIO with pr_info("%s: %#lx: unknown zero refcount page type %lx\n", so mce_bad_pages will not be added.

Signed-off-by Xishi Qiu <[email protected]>

i>>?Signed-off-by: Jiang Liu <[email protected]>

---
 mm/memory-failure.c |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)

mm/memory-failure.c +0 -0

index 8b20278..02a522e 100644

mm/memory-failure.c static int get_any_page(struct page *p, unsigned long pfn, int flags) · line 1381

Quoted 7 lines

mm/memory-failure.c +4 -0

@@ -1375,6 +1375,11 @@ static int get_any_page(struct page *p, unsigned long pfn, int flags)
 	if (flags & MF_COUNT_INCREASED)
 		return 1;
 
+	if (PageHWPoison(p)) {
+		pr_info("%s: %#lx page already poisoned\n", __func__, pfn);
+		return -EBUSY;
+	}

Shouldn't this be done in soft_offline_page() instead, like it is done in soft_offline_huge_page() for hugepages?

Thanks.

Hi Borislav, you mean we should move this to the beginning of soft_offline_page()?

soft_offline_page()

{
	...
	get_any_page()
	...
	/*
	 * Synchronized using the page lock with memory_failure()
	 */
	if (PageHWPoison(page)) {
		unlock_page(page);