[PATCH v2 3/3] mm/hwpoison: don't try to unpoison containment-failed pages

[Naoya Horiguchi]

memory_failure() can be called at any page at any time, which means that we
can't eliminate the possibility of containment failure. In such case the best
option is to leak the page intentionally (and never touch it later.)

We have an unpoison function for testing, and it cannot handle such
containment-failed pages, which results in kernel panic (visible with various
calltraces.) So this patch suggests that we limit the unpoisonable pages to
properly contained pages and ignore any other ones.

Testers are recommended to keep in mind that there're un-unpoisonable pages
when writing test programs.

Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
---
 mm/memory-failure.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git mmotm-2015-08-13-15-29.orig/mm/memory-failure.c mmotm-2015-08-13-15-29/mm/memory-failure.c
index 7986db56e240..613389e9e5a8 100644
--- mmotm-2015-08-13-15-29.orig/mm/memory-failure.c
+++ mmotm-2015-08-13-15-29/mm/memory-failure.c
@@ -1433,6 +1433,22 @@ int unpoison_memory(unsigned long pfn)
 		return 0;
 	}
 
+	if (page_count(page) > 1) {
+		pr_info("MCE: Someone grabs the hwpoison page %#lx\n", pfn);
+		return 0;
+	}
+
+	if (page_mapped(page)) {
+		pr_info("MCE: Someone maps the hwpoison page %#lx\n", pfn);
+		return 0;
+	}
+
+	if (page_mapping(page)) {
+		pr_info("MCE: the hwpoison page has non-NULL mapping %#lx\n",
+			pfn);
+		return 0;
+	}
+
 	/*
 	 * unpoison_memory() can encounter thp only when the thp is being
 	 * worked by memory_failure() and the page lock is not held yet.
-- 
2.4.3
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