NFS: Don't corrupt the value of pg_bytes_written in nfs_do_recoalesce()

ANBZ: torvalds#752

commit 0d0ea30 upstream.

The value of mirror->pg_bytes_written should only be updated after a
successful attempt to flush out the requests on the list.

Fixes: a7d42dd ("nfs: add mirroring support to pgio layer")
Signed-off-by: Trond Myklebust <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Signed-off-by: Joseph Qi <[email protected]>
Reviewed-by: Gao Xiang <[email protected]>

fs/nfs/pagelist.c

@@ -964,17 +964,16 @@ static void nfs_pageio_doio(struct nfs_pageio_descriptor *desc)
 {
 	struct nfs_pgio_mirror *mirror = nfs_pgio_current_mirror(desc);
 
-
 	if (!list_empty(&mirror->pg_list)) {
 		int error = desc->pg_ops->pg_doio(desc);
 		if (error < 0)
 			desc->pg_error = error;
-		else
+		if (list_empty(&mirror->pg_list)) {
 			mirror->pg_bytes_written += mirror->pg_count;
-	}
-	if (list_empty(&mirror->pg_list)) {
-		mirror->pg_count = 0;
-		mirror->pg_base = 0;
+			mirror->pg_count = 0;
+			mirror->pg_base = 0;
+			mirror->pg_recoalesce = 0;
+		}
 	}
 }
 
@@ -1072,7 +1071,6 @@ static int nfs_do_recoalesce(struct nfs_pageio_descriptor *desc)
 
 	do {
 		list_splice_init(&mirror->pg_list, &head);
-		mirror->pg_bytes_written -= mirror->pg_count;
 		mirror->pg_count = 0;
 		mirror->pg_base = 0;
 		mirror->pg_recoalesce = 0;