quota: Push dqio_sem down to ->read_dqblk()

Push down acquisition of dqio_sem into ->read_dqblk() callback. It will
allow quota formats to decide whether they need it or not.
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Signed-off-by: Jan Kara <jack@suse.cz>

fs/quota/dquot.c

@@ -403,11 +403,8 @@ int dquot_acquire(struct dquot *dquot)
 	struct quota_info *dqopt = sb_dqopt(dquot->dq_sb);
 
 	mutex_lock(&dquot->dq_lock);
-	if (!test_bit(DQ_READ_B, &dquot->dq_flags)) {
-		down_read(&dqopt->dqio_sem);
+	if (!test_bit(DQ_READ_B, &dquot->dq_flags))
 		ret = dqopt->ops[dquot->dq_id.type]->read_dqblk(dquot);
-		up_read(&dqopt->dqio_sem);
-	}
 	if (ret < 0)
 		goto out_iolock;
 	/* Make sure flags update is visible after dquot has been filled */

fs/quota/quota_v1.c

@@ -56,10 +56,12 @@ static int v1_read_dqblk(struct dquot *dquot)
 {
 	int type = dquot->dq_id.type;
 	struct v1_disk_dqblk dqblk;
+	struct quota_info *dqopt = sb_dqopt(dquot->dq_sb);
 
-	if (!sb_dqopt(dquot->dq_sb)->files[type])
+	if (!dqopt->files[type])
 		return -EINVAL;
 
+	down_read(&dqopt->dqio_sem);
 	/* Set structure to 0s in case read fails/is after end of file */
 	memset(&dqblk, 0, sizeof(struct v1_disk_dqblk));
 	dquot->dq_sb->s_op->quota_read(dquot->dq_sb, type, (char *)&dqblk,
@@ -73,6 +75,7 @@ static int v1_read_dqblk(struct dquot *dquot)
 	    dquot->dq_dqb.dqb_isoftlimit == 0)
 		set_bit(DQ_FAKE_B, &dquot->dq_flags);
 	dqstats_inc(DQST_READS);
+	up_read(&dqopt->dqio_sem);
 
 	return 0;
 }

fs/quota/quota_v2.c

@@ -285,7 +285,15 @@ static int v2r1_is_id(void *dp, struct dquot *dquot)
 
 static int v2_read_dquot(struct dquot *dquot)
 {
-	return qtree_read_dquot(sb_dqinfo(dquot->dq_sb, dquot->dq_id.type)->dqi_priv, dquot);
+	struct quota_info *dqopt = sb_dqopt(dquot->dq_sb);
+	int ret;
+
+	down_read(&dqopt->dqio_sem);
+	ret = qtree_read_dquot(
+			sb_dqinfo(dquot->dq_sb, dquot->dq_id.type)->dqi_priv,
+			dquot);
+	up_read(&dqopt->dqio_sem);
+	return ret;
 }
 
 static int v2_write_dquot(struct dquot *dquot)