From 23e7b5c2e2715947cf1ff57124dd3e96caf48521 Mon Sep 17 00:00:00 2001
From: Dan Williams <dan.j.williams@intel.com>
Date: Fri, 13 Jul 2018 21:50:06 -0700
Subject: [PATCH] mm, madvise_inject_error: Let memory_failure() optionally
 take a page reference
Git-commit: 23e7b5c2e2715947cf1ff57124dd3e96caf48521
Patch-mainline: v4.19-rc1
References: bsc#1107783

The madvise_inject_error() routine uses get_user_pages() to lookup the
pfn and other information for injected error, but it does not release
that pin. The assumption is that failed pages should be taken out of
circulation.

However, for dax mappings it is not possible to take pages out of
circulation since they are 1:1 physically mapped as filesystem blocks,
or device-dax capacity. They also typically represent persistent memory
which has an error clearing capability.

In preparation for adding a special handler for dax mappings, shift the
responsibility of taking the page reference to memory_failure(). I.e.
drop the page reference and do not specify MF_COUNT_INCREASED to
memory_failure().

Cc: Michal Hocko <mhocko@suse.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Acked-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Acked-by: Jan Kara <jack@suse.cz>

---
 mm/madvise.c |   15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -616,11 +616,13 @@ static int madvise_inject_error(int beha
 
 
 	for (; start < end; start += PAGE_SIZE << order) {
+		unsigned long pfn;
 		int ret;
 
 		ret = get_user_pages_fast(start, 1, 0, &page);
 		if (ret != 1)
 			return ret;
+		pfn = page_to_pfn(page);
 
 		/*
 		 * When soft offlining hugepages, after migrating the page
@@ -636,7 +638,7 @@ static int madvise_inject_error(int beha
 
 		if (behavior == MADV_SOFT_OFFLINE) {
 			pr_info("Soft offlining pfn %#lx at process virtual address %#lx\n",
-						page_to_pfn(page), start);
+					pfn, start);
 
 			ret = soft_offline_page(page, MF_COUNT_INCREASED);
 			if (ret)
@@ -644,9 +646,16 @@ static int madvise_inject_error(int beha
 			continue;
 		}
 		pr_info("Injecting memory failure for pfn %#lx at process virtual address %#lx\n",
-						page_to_pfn(page), start);
+				pfn, start);
 
-		ret = memory_failure(page_to_pfn(page), 0, MF_COUNT_INCREASED);
+		/*
+		 * Drop the page reference taken by get_user_pages_fast(). In
+		 * the absence of MF_COUNT_INCREASED the memory_failure()
+		 * routine is responsible for pinning the page to prevent it
+		 * from being released back to the page allocator.
+		 */
+		put_page(page);
+		ret = memory_failure(pfn, 0, 0);
 		if (ret)
 			return ret;
 	}