From 7f6bf39bbdd1dcccd103ba7dce8496a8e72e7df4 Mon Sep 17 00:00:00 2001
From: Wanpeng Li <wanpeng.li@hotmail.com>
Date: Fri, 14 Aug 2015 15:35:08 -0700
Subject: mm/hwpoison: fix panic due to split huge zero page

Bug:

  ------------[ cut here ]------------
  kernel BUG at mm/huge_memory.c:1957!
  invalid opcode: 0000 [#1] SMP
  Modules linked in: snd_hda_codec_hdmi i915 rpcsec_gss_krb5 snd_hda_codec_realtek snd_hda_codec_generic nfsv4 dns_re
  CPU: 2 PID: 2576 Comm: test_huge Not tainted 4.2.0-rc5-mm1+ #27
  Hardware name: Dell Inc. OptiPlex 7020/0F5C5X, BIOS A03 01/08/2015
  task: ffff880204e3d600 ti: ffff8800db16c000 task.ti: ffff8800db16c000
  RIP: split_huge_page_to_list+0xdb/0x120
  Call Trace:
    memory_failure+0x32e/0x7c0
    madvise_hwpoison+0x8b/0x160
    SyS_madvise+0x40/0x240
    ? do_page_fault+0x37/0x90
    entry_SYSCALL_64_fastpath+0x12/0x71
  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
  RIP  split_huge_page_to_list+0xdb/0x120
   RSP <ffff8800db16fde8>
  ---[ 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 98ed2b0052e6 ("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 this patch:

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

[akpm@linux-foundation.org: remove second split, per Wanpeng]
Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
Acked-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
 mm/memory-failure.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

(limited to 'mm')

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index dba52ee31bd4..1f4446a90cef 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1146,8 +1146,11 @@ 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
+				pr_err("MCE: %#lx: thp split failed\n", pfn);
 			if (TestClearPageHWPoison(p))
 				atomic_long_sub(nr_pages, &num_poisoned_pages);
 			put_page(p);
-- 
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