[PATCH AUTOSEL 4.20 36/52] NFS: Don't use page_file_mapping after removing the page

[Sasha Levin]

From: Benjamin Coddington <bcodding@xxxxxxxxxx>

[ Upstream commit d2ceb7e57086750ea6198a31fd942d98099a0786 ]

If nfs_page_async_flush() removes the page from the mapping, then we can't
use page_file_mapping() on it as nfs_updatepate() is wont to do when
receiving an error.  Instead, push the mapping to the stack before the page
is possibly truncated.

Fixes: 8fc75bed96bb ("NFS: Fix up return value on fatal errors in nfs_page_async_flush()")
Signed-off-by: Benjamin Coddington <bcodding@xxxxxxxxxx>
Signed-off-by: Anna Schumaker <Anna.Schumaker@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 fs/nfs/write.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index d790faff8e47..51d0b7913c04 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -238,9 +238,9 @@ static void nfs_grow_file(struct page *page, unsigned int offset, unsigned int c
 }
 
 /* A writeback failed: mark the page as bad, and invalidate the page cache */
-static void nfs_set_pageerror(struct page *page)
+static void nfs_set_pageerror(struct address_space *mapping)
 {
-	nfs_zap_mapping(page_file_mapping(page)->host, page_file_mapping(page));
+	nfs_zap_mapping(mapping->host, mapping);
 }
 
 /*
@@ -994,7 +994,7 @@ static void nfs_write_completion(struct nfs_pgio_header *hdr)
 		nfs_list_remove_request(req);
 		if (test_bit(NFS_IOHDR_ERROR, &hdr->flags) &&
 		    (hdr->good_bytes < bytes)) {
-			nfs_set_pageerror(req->wb_page);
+			nfs_set_pageerror(page_file_mapping(req->wb_page));
 			nfs_context_set_write_error(req->wb_context, hdr->error);
 			goto remove_req;
 		}
@@ -1330,7 +1330,8 @@ int nfs_updatepage(struct file *file, struct page *page,
 		unsigned int offset, unsigned int count)
 {
 	struct nfs_open_context *ctx = nfs_file_open_context(file);
-	struct inode	*inode = page_file_mapping(page)->host;
+	struct address_space *mapping = page_file_mapping(page);
+	struct inode	*inode = mapping->host;
 	int		status = 0;
 
 	nfs_inc_stats(inode, NFSIOS_VFSUPDATEPAGE);
@@ -1348,7 +1349,7 @@ int nfs_updatepage(struct file *file, struct page *page,
 
 	status = nfs_writepage_setup(ctx, page, offset, count);
 	if (status < 0)
-		nfs_set_pageerror(page);
+		nfs_set_pageerror(mapping);
 	else
 		__set_page_dirty_nobuffers(page);
 out:
-- 
2.19.1