JFFS2: don't fail on bitflips in OOB

commit 74d83bea upstream.

JFFS2 was designed without thought for OOB bitflips, it seems, but they
can occur and will be reported to JFFS2 via mtd_read_oob()[1]. We don't
want to fail on these transactions, since the data was corrected.

[1] Few drivers report bitflips for OOB-only transactions. With such
    drivers, this patch should have no effect.
Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

fs/jffs2/wbuf.c

@@ -1032,11 +1032,11 @@ int jffs2_check_oob_empty(struct jffs2_sb_info *c,
 	ops.datbuf = NULL;
 
 	ret = c->mtd->read_oob(c->mtd, jeb->offset, &ops);
-	if (ret || ops.oobretlen != ops.ooblen) {
+	if ((ret && !mtd_is_bitflip(ret)) || ops.oobretlen != ops.ooblen) {
 		printk(KERN_ERR "cannot read OOB for EB at %08x, requested %zd"
 				" bytes, read %zd bytes, error %d\n",
 				jeb->offset, ops.ooblen, ops.oobretlen, ret);
-		if (!ret)
+		if (!ret || mtd_is_bitflip(ret))
 			ret = -EIO;
 		return ret;
 	}
@@ -1075,11 +1075,11 @@ int jffs2_check_nand_cleanmarker(struct jffs2_sb_info *c,
 	ops.datbuf = NULL;
 
 	ret = c->mtd->read_oob(c->mtd, jeb->offset, &ops);
-	if (ret || ops.oobretlen != ops.ooblen) {
+	if ((ret && !mtd_is_bitflip(ret)) || ops.oobretlen != ops.ooblen) {
 		printk(KERN_ERR "cannot read OOB for EB at %08x, requested %zd"
 				" bytes, read %zd bytes, error %d\n",
 				jeb->offset, ops.ooblen, ops.oobretlen, ret);
-		if (!ret)
+		if (!ret || mtd_is_bitflip(ret))
 			ret = -EIO;
 		return ret;
 	}