[PATCH 1/3] mm/hwpoison: fix memory failure still hold reference count after unpoison empty zero page

[PATCH 1/3] mm/hwpoison: fix memory failure still hold reference count after unpoison empty zero page

[Wanpeng Li]

madvise hwpoison inject will poison the read-only empty zero page if there is 
no write access before poison. Empty zero page reference count will be increased 
for hwpoison, subsequent poison zero page will return directly since page has
already been set PG_hwpoison, however, page reference count is still increased 
by get_user_pages_fast. The unpoison process will unpoison the empty zero page 
and decrease the reference count successfully for the fist time, however, 
subsequent unpoison empty zero page will return directly since page has already 
been unpoisoned and without decrease the page reference count of empty zero page.
This patch fix it by make madvise_hwpoison() put a page and return immediately
(without calling memory_failure() or soft_offline_page()) when the page is already 
hwpoisoned.

Testcase:

#define _GNU_SOURCE
#include <stdlib.h>
#include <stdio.h>
#include <sys/mman.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/types.h>
#include <errno.h>

#define PAGES_TO_TEST 3
#define PAGE_SIZE	4096

int main(void)
{
	char *mem;
	int i;

	mem = mmap(NULL, PAGES_TO_TEST * PAGE_SIZE,
			PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, 0, 0);

	if (madvise(mem, PAGES_TO_TEST * PAGE_SIZE, MADV_HWPOISON) == -1)
		return -1;
	
	munmap(mem, PAGES_TO_TEST * PAGE_SIZE);

	return 0;
}

Add printk to dump page reference count:

[   93.075959] Injecting memory failure for page 0x19d0 at 0xb77d8000
[   93.076207] MCE 0x19d0: non LRU page recovery: Ignored
[   93.076209] pfn 0x19d0, page count = 1 after memory failure
[   93.076220] Injecting memory failure for page 0x19d0 at 0xb77d9000
[   93.076221] MCE 0x19d0: already hardware poisoned
[   93.076222] pfn 0x19d0, page count = 2 after memory failure
[   93.076224] Injecting memory failure for page 0x19d0 at 0xb77da000
[   93.076224] MCE 0x19d0: already hardware poisoned
[   93.076225] pfn 0x19d0, page count = 3 after memory failure

Suggested-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Signed-off-by: Wanpeng Li <liwanp@linux.vnet.ibm.com>
---
 mm/madvise.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/mm/madvise.c b/mm/madvise.c
index 212f5f1..0956ae9 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -352,6 +352,10 @@ static int madvise_hwpoison(int bhv, unsigned long start, unsigned long end)
 		int ret = get_user_pages_fast(start, 1, 0, &p);
 		if (ret != 1)
 			return ret;
+		if (PageHWPoison(p)) {
+			put_page(p);
+			continue;
+		}
 		if (bhv == MADV_SOFT_OFFLINE) {
 			pr_info("Soft offlining page %#lx at %#lx\n",
 				page_to_pfn(p), start);
-- 
1.8.1.2

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[PATCH 2/3] mm/hwpoison: change permission of corrupt-pfn/unpoison-pfn to 0200

[Wanpeng Li]

Hwpoison inject doesn't implement read method for corrupt-pfn/unpoison-pfn
attributes:

# cat /sys/kernel/debug/hwpoison/corrupt-pfn
cat: /sys/kernel/debug/hwpoison/corrupt-pfn: Permission denied
# cat /sys/kernel/debug/hwpoison/unpoison-pfn
cat: /sys/kernel/debug/hwpoison/unpoison-pfn: Permission denied

This patch change the permission of corrupt-pfn/unpoison-pfn to 0200.

Reviewed-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Signed-off-by: Wanpeng Li <liwanp@linux.vnet.ibm.com>
---
 mm/hwpoison-inject.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/hwpoison-inject.c b/mm/hwpoison-inject.c
index 3a61efc..afc2daa 100644
--- a/mm/hwpoison-inject.c
+++ b/mm/hwpoison-inject.c
@@ -88,12 +88,12 @@ static int pfn_inject_init(void)
 	 * hardware status change, hence do not require hardware support.
 	 * They are mainly for testing hwpoison in software level.
 	 */
-	dentry = debugfs_create_file("corrupt-pfn", 0600, hwpoison_dir,
+	dentry = debugfs_create_file("corrupt-pfn", 0200, hwpoison_dir,
 					  NULL, &hwpoison_fops);
 	if (!dentry)
 		goto fail;
 
-	dentry = debugfs_create_file("unpoison-pfn", 0600, hwpoison_dir,
+	dentry = debugfs_create_file("unpoison-pfn", 0200, hwpoison_dir,
 				     NULL, &unpoison_fops);
 	if (!dentry)
 		goto fail;
-- 
1.8.1.2

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[PATCH 3/3] mm/hwpoison: fix bug triggered by unpoison empty zero page

[Wanpeng Li]

[   57.579580] Injecting memory failure for page 0x19d0 at 0xb77d2000
[   57.579824] MCE 0x19d0: non LRU page recovery: Ignored
[   91.290453] MCE: Software-unpoisoned page 0x19d0
[   91.290456] BUG: Bad page state in process bash  pfn:019d0
[   91.290466] page:f3461a00 count:0 mapcount:0 mapping:  (null) index:0x0
[   91.290467] page flags: 0x40000404(referenced|reserved)
[   91.290469] Modules linked in: nfsd auth_rpcgss i915 nfs_acl nfs lockd video drm_kms_helper drm bnep rfcomm sunrpc bluetooth psmouse parport_pc ppdev lp serio_raw fscache parport gpio_ich lpc_ich mac_hid i2c_algo_bit tpm_tis wmi usb_storage hid_generic usbhid hid e1000e firewire_ohci firewire_core ahci ptp libahci pps_core crc_itu_t
[   91.290486] CPU: 3 PID: 2123 Comm: bash Not tainted 3.11.0-rc6+ #12
[   91.290487] Hardware name: LENOVO 7034DD7/        , BIOS 9HKT47AUS 01//2012
[   91.290488]  00000000 00000000 e9625ea0 c15ec49b f3461a00 e9625eb8 c15ea119 c17cbf18
[   91.290491]  ef084314 000019d0 f3461a00 e9625ed8 c110dc8a f3461a00 00000001 00000000
[   91.290494]  f3461a00 40000404 00000000 e9625ef8 c110dcc1 f3461a00 f3461a00 000019d0
[   91.290497] Call Trace:
[   91.290501]  [<c15ec49b>] dump_stack+0x41/0x52
[   91.290504]  [<c15ea119>] bad_page+0xcf/0xeb
[   91.290515]  [<c110dc8a>] free_pages_prepare+0x12a/0x140
[   91.290517]  [<c110dcc1>] free_hot_cold_page+0x21/0x110
[   91.290519]  [<c11123c1>] __put_single_page+0x21/0x30
[   91.290521]  [<c1112815>] put_page+0x25/0x40
[   91.290524]  [<c11544e7>] unpoison_memory+0x107/0x200
[   91.290526]  [<c104a537>] ? ns_capable+0x27/0x60
[   91.290528]  [<c1155720>] hwpoison_unpoison+0x20/0x30
[   91.290530]  [<c1178266>] simple_attr_write+0xb6/0xd0
[   91.290532]  [<c11781b0>] ? generic_fh_to_dentry+0x50/0x50
[   91.290535]  [<c1158c60>] vfs_write+0xa0/0x1b0
[   91.290537]  [<c11781b0>] ? generic_fh_to_dentry+0x50/0x50
[   91.290539]  [<c11590df>] SyS_write+0x4f/0x90
[   91.290549]  [<c15f9a81>] sysenter_do_call+0x12/0x22
[   91.290550] Disabling lock debugging due to kernel taint

Testcase:

#define _GNU_SOURCE
#include <stdlib.h>
#include <stdio.h>
#include <sys/mman.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/types.h>
#include <errno.h>

#define PAGES_TO_TEST 1
#define PAGE_SIZE	4096

int main(void)
{
	char *mem;

	mem = mmap(NULL, PAGES_TO_TEST * PAGE_SIZE,
			PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, 0, 0);

	if (madvise(mem, PAGES_TO_TEST * PAGE_SIZE, MADV_HWPOISON) == -1)
		return -1;

	munmap(mem, PAGES_TO_TEST * PAGE_SIZE);

	return 0;
}

There is one page reference count for default empty zero page, madvise_hwpoison
add another one by get_user_pages_fast. memory_hwpoison reduce one page reference
count since it's a non LRU page. unpoison_memory release the last page reference
count and free empty zero page to buddy system which is not correct since empty
zero page has PG_reserved flag. This patch fix it by don't reduce the page
reference count under 1 against empty zero page.

Signed-off-by: Wanpeng Li <liwanp@linux.vnet.ibm.com>
---
 mm/memory-failure.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 7cdabc0..657c0c1 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1385,7 +1385,7 @@ int unpoison_memory(unsigned long pfn)
 	unlock_page(page);
 
 	put_page(page);
-	if (freeit)
+	if (freeit && !(pfn == my_zero_pfn(0) && page_count(p) == 1))
 		put_page(page);
 
 	return 0;
-- 
1.8.1.2

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