[PATCH] mm/hwpoison: fix panic due to split huge zero page

[Wanpeng Li <wanpeng.li@hotmail.com>]

[ 1162.009854] ------------[ cut here ]------------
[ 1162.014485] kernel BUG at mm/huge_memory.c:1957!
[ 1162.019109] invalid opcode: 0000 [#1] SMP 
[ 1162.023236] Modules linked in: snd_hda_codec_hdmi i915 rpcsec_gss_krb5 snd_hda_codec_realtek snd_hda_codec_generic nfsv4 dns_re
[ 1162.090181] CPU: 2 PID: 2576 Comm: test_huge Not tainted 4.2.0-rc5-mm1+ #27
[ 1162.097150] Hardware name: Dell Inc. OptiPlex 7020/0F5C5X, BIOS A03 01/08/2015
[ 1162.104378] task: ffff880204e3d600 ti: ffff8800db16c000 task.ti: ffff8800db16c000
[ 1162.111867] RIP: 0010:[<ffffffff811dea3b>]  [<ffffffff811dea3b>] split_huge_page_to_list+0xdb/0x120
[ 1162.120933] RSP: 0018:ffff8800db16fde8  EFLAGS: 00010246
[ 1162.126246] RAX: ffffea0002310000 RBX: ffffea0002310000 RCX: ffff88021edd2000
[ 1162.133383] RDX: 0000000000000011 RSI: 0000000000000000 RDI: ffffea0002310000
[ 1162.140530] RBP: ffff8800db16fe08 R08: 000000000000fffe R09: 0000000000000001
[ 1162.147668] R10: 0000000000000326 R11: 0000000000000326 R12: 000000000008c400
[ 1162.154809] R13: 0000000000000000 R14: 0000000000000001 R15: 0000000000000000
[ 1162.161947] FS:  00007f36f7d2e740(0000) GS:ffff88021eb00000(0000) knlGS:0000000000000000
[ 1162.170043] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1162.175794] CR2: 00007f36eadffff8 CR3: 00000000a75db000 CR4: 00000000001406e0
[ 1162.182931] Stack:
[ 1162.184943]  ffff8800db16fe80 ffffea0002310000 000000000008c400 0000000000000001
[ 1162.192391]  ffff8800db16fe68 ffffffff811ecb4e ffffea0002310000 0000000000000001
[ 1162.199834]  ffff8800db16fe38 ffffea0002310000 ffff8800db16fe58 00007f36eae00000
[ 1162.207278] Call Trace:
[ 1162.209726]  [<ffffffff811ecb4e>] memory_failure+0x32e/0x7c0
[ 1162.215388]  [<ffffffff811b9f1b>] madvise_hwpoison+0x8b/0x160
[ 1162.221134]  [<ffffffff811ba680>] SyS_madvise+0x40/0x240
[ 1162.226450]  [<ffffffff81066777>] ? do_page_fault+0x37/0x90
[ 1162.232024]  [<ffffffff8166152e>] entry_SYSCALL_64_fastpath+0x12/0x71
[ 1162.238467] Code: ff f0 41 ff 4c 24 30 74 0d 31 c0 48 83 c4 08 5b 41 5c 41 5d c9 c3 4c 89 e7 e8 e2 58 fd ff 48 83 c4 08 31 c0  
[ 1162.258104] RIP  [<ffffffff811dea3b>] split_huge_page_to_list+0xdb/0x120
[ 1162.264815]  RSP <ffff8800db16fde8>
[ 1162.273447] ---[ end trace aee7ce0df8e44076 ]---

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>
#include <string.h>

#define MB 1024*1024

int main(void)
{
	char *mem;

	posix_memalign((void **)&mem, 2 * MB, 200 * MB);

	madvise(mem, 200 * MB, MADV_HWPOISON);

	free(mem);

	return 0;
}

Huge zero page is allocated if page fault w/o FAULT_FLAG_WRITE flag. 
The get_user_pages_fast() which called in madvise_hwpoison() will get 
huge zero page if the page is not allocated before. Huge zero page is 
a tranparent huge page, however, it is not an anonymous page. memory_failure 
will split the huge zero page and trigger BUG_ON(is_huge_zero_page(page)); 
After commit (98ed2b0: mm/memory-failure: give up error handling for 
non-tail-refcounted thp), memory_failure will not catch non anon thp 
from madvise_hwpoison path and this bug occur.

Fix it by catching non anon thp in memory_failure in order to not split 
huge zero page in madvise_hwpoison path.

After patch:

[   51.825205] Injecting memory failure for page 0x202800 at 0x7fd8ae800000
[   51.825205] MCE: 0x202800: non anonymous thp
[...]

Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
---
Note: the patch is rebased on put_hwpoison_page() patches.

 mm/memory-failure.c |    7 +++++--
 1 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 6179fc1..0acafee 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1155,8 +1155,11 @@ int memory_failure(unsigned long pfn, int trapno, int flags)
 	}
 
 	if (!PageHuge(p) && PageTransHuge(hpage)) {
-		if (unlikely(split_huge_page(hpage))) {
-			pr_err("MCE: %#lx: thp split failed\n", pfn);
+		if (!PageAnon(hpage) || unlikely(split_huge_page(hpage))) {
+			if (!PageAnon(hpage))
+				pr_err("MCE: %#lx: non anonymous thp\n", pfn);
+			else if (unlikely(split_huge_page(hpage)))
+				pr_err("MCE: %#lx: thp split failed\n", pfn);
 			if (TestClearPageHWPoison(p))
 				atomic_long_sub(nr_pages, &num_poisoned_pages);
 			put_hwpoison_page(p);
-- 
1.7.1

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