hwpoison: fix the handling path of the victimized page frame that belong to non-LRU

Until now, the kernel has the same policy to handle victimized page
frames that belong to kernel-space(reserved/slab-subsystem) or
non-LRU(unknown page state).  In other word, the result of handling
either of these victimized page frames is (IGNORED | FAILED), and the
return value of memory_failure() is -EBUSY.

This patch is to avoid that memory_failure() returns very soon due to
the "true" value of (!PageLRU(p)), and it also ensures that
action_result() can report more precise information("reserved kernel",
"kernel slab", and "unknown page state") instead of "non LRU",
especially for memory errors which are detected by memory-scrubbing.

Andi said:

: While running the mcelog test suite on 3.14 I hit the following VM_BUG_ON:
:
: soft_offline: 0x56d4: unknown non LRU page type 3ffff800008000
: page:ffffea000015b400 count:3 mapcount:2097169 mapping:          (null) index:0xffff8800056d7000
: page flags: 0x3ffff800004081(locked|slab|head)
: ------------[ cut here ]------------
: kernel BUG at mm/rmap.c:1495!
:
: I think what happened is that a LRU page turned into a slab page in
: parallel with offlining.  memory_failure initially tests for this case,
: but doesn't retest later after the page has been locked.
:
: ...
:
: I ran this patch in a loop over night with some stress plus
: the mcelog test suite running in a loop. I cannot guarantee it hit it,
: but it should have given it a good beating.
:
: The kernel survived with no messages, although the mcelog test suite
: got killed at some point because it couldn't fork anymore. Probably
: some unrelated problem.
:
: So the patch is ok for me for .16.

Signed-off-by: Chen Yucong <slaoub@gmail.com>
Acked-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Reported-by: Andi Kleen <andi@firstfloor.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memory-failure.c

@@ -895,7 +895,7 @@ static int hwpoison_user_mappings(struct page *p, unsigned long pfn,
 	struct page *hpage = *hpagep;
 	struct page *ppage;
 
-	if (PageReserved(p) || PageSlab(p))
+	if (PageReserved(p) || PageSlab(p) || !PageLRU(p))
 		return SWAP_SUCCESS;
 
 	/*
@@ -1159,9 +1159,6 @@ int memory_failure(unsigned long pfn, int trapno, int flags)
 					action_result(pfn, "free buddy, 2nd try", DELAYED);
 				return 0;
 			}
-			action_result(pfn, "non LRU", IGNORED);
-			put_page(p);
-			return -EBUSY;
 		}
 	}
 
@@ -1194,6 +1191,9 @@ int memory_failure(unsigned long pfn, int trapno, int flags)
 		return 0;
 	}
 
+	if (!PageHuge(p) && !PageTransTail(p) && !PageLRU(p))
+		goto identify_page_state;
+
 	/*
 	 * For error on the tail page, we should set PG_hwpoison
 	 * on the head page to show that the hugepage is hwpoisoned
@@ -1243,6 +1243,7 @@ int memory_failure(unsigned long pfn, int trapno, int flags)
 		goto out;
 	}
 
+identify_page_state:
 	res = -EBUSY;
 	/*
 	 * The first check uses the current page flags which may not have any