From 2fa147bdbf672c53386a8f5f2c7fe358004c3ef8 Mon Sep 17 00:00:00 2001
From: Dan Williams <dan.j.williams@intel.com>
Date: Fri, 13 Jul 2018 21:50:01 -0700
Subject: [PATCH] mm, dev_pagemap: Do not clear ->mapping on final put
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Git-commit: 2fa147bdbf672c53386a8f5f2c7fe358004c3ef8
Patch-mainline: v4.19-rc1
References: bsc#1104888

MEMORY_DEVICE_FS_DAX relies on typical page semantics whereby ->mapping
is only ever cleared by truncation, not final put.

Without this fix dax pages may forget their mapping association at the
end of every page pin event.

Move this atypical behavior that HMM wants into the HMM ->page_free()
callback.

Cc: <stable@vger.kernel.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Jérôme Glisse <jglisse@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Fixes: d2c997c0f145 ("fs, dax: use page->mapping...")
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Acked-by: Jérôme Glisse <jglisse@redhat.com>
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Acked-by: Jan Kara <jack@suse.cz>

---
 kernel/memremap.c | 1 -
 mm/hmm.c          | 2 ++
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/memremap.c b/kernel/memremap.c
index 5857267a4af5..62603634a1d2 100644
--- a/kernel/memremap.c
+++ b/kernel/memremap.c
@@ -339,7 +339,6 @@ void __put_devmap_managed_page(struct page *page)
 		__ClearPageActive(page);
 		__ClearPageWaiters(page);
 
-		page->mapping = NULL;
 		mem_cgroup_uncharge(page);
 
 		page->pgmap->page_free(page, page->pgmap->data);
diff --git a/mm/hmm.c b/mm/hmm.c
index de7b6bf77201..f9d1d89dec4d 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -963,6 +963,8 @@ static void hmm_devmem_free(struct page *page, void *data)
 {
 	struct hmm_devmem *devmem = data;
 
+	page->mapping = NULL;
+
 	devmem->ops->free(devmem, page);
 }
 
-- 
2.16.4