gfs2: Check quota consistency on mount

In gfs2_quota_init(), make sure that the per-node "quota_change%u" file
doesn't contain duplicate uids/gids.  Those duplicates would cause us to
acquire the glock corresponding to those ids repeatedly, which the glock
code doesn't allow.

When finding inconsistencies, we wipe them out and ignore them.  The
resulting quotas will likely be inconsistent, and running quotacheck(1)
is advised.
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>

fs/gfs2/quota.c

@@ -1427,7 +1427,7 @@ int gfs2_quota_init(struct gfs2_sbd *sdp)
 		return error;
 
 	for (x = 0; x < blocks; x++) {
-		const struct gfs2_quota_change *qc;
+		struct gfs2_quota_change *qc;
 		unsigned int y;
 
 		if (!extlen) {
@@ -1443,10 +1443,10 @@ int gfs2_quota_init(struct gfs2_sbd *sdp)
 		if (gfs2_metatype_check(sdp, bh, GFS2_METATYPE_QC))
 			goto fail_brelse;
 
-		qc = (const struct gfs2_quota_change *)(bh->b_data + sizeof(struct gfs2_meta_header));
+		qc = (struct gfs2_quota_change *)(bh->b_data + sizeof(struct gfs2_meta_header));
 		for (y = 0; y < sdp->sd_qc_per_block && slot < sdp->sd_quota_slots;
 		     y++, slot++) {
-			struct gfs2_quota_data *qd;
+			struct gfs2_quota_data *old_qd, *qd;
 			s64 qc_change = be64_to_cpu(qc->qc_change);
 			u32 qc_flags = be32_to_cpu(qc->qc_flags);
 			enum quota_type qtype = (qc_flags & GFS2_QCF_USER) ?
@@ -1468,18 +1468,41 @@ int gfs2_quota_init(struct gfs2_sbd *sdp)
 			qd->qd_slot_ref = 1;
 
 			spin_lock(&qd_lock);
+			spin_lock_bucket(hash);
+			old_qd = gfs2_qd_search_bucket(hash, sdp, qc_id);
+			if (old_qd) {
+				fs_err(sdp, "Corruption found in quota_change%u"
+					    "file: duplicate identifier in "
+					    "slot %u\n",
+					    sdp->sd_jdesc->jd_jid, slot);
+
+				spin_unlock_bucket(hash);
+				spin_unlock(&qd_lock);
+				qd_put(old_qd);
+
+				gfs2_glock_put(qd->qd_gl);
+				kmem_cache_free(gfs2_quotad_cachep, qd);
+
+				/* zero out the duplicate slot */
+				lock_buffer(bh);
+				memset(qc, 0, sizeof(*qc));
+				mark_buffer_dirty(bh);
+				unlock_buffer(bh);
+
+				continue;
+			}
 			BUG_ON(test_and_set_bit(slot, sdp->sd_quota_bitmap));
 			list_add(&qd->qd_list, &sdp->sd_quota_list);
 			atomic_inc(&sdp->sd_quota_count);
-			spin_unlock(&qd_lock);
-
-			spin_lock_bucket(hash);
 			hlist_bl_add_head_rcu(&qd->qd_hlist, &qd_hash_table[hash]);
 			spin_unlock_bucket(hash);
+			spin_unlock(&qd_lock);
 
 			found++;
 		}
 
+		if (buffer_dirty(bh))
+			sync_dirty_buffer(bh);
 		brelse(bh);
 		dblock++;
 		extlen--;
@@ -1491,6 +1514,8 @@ int gfs2_quota_init(struct gfs2_sbd *sdp)
 	return 0;
 
 fail_brelse:
+	if (buffer_dirty(bh))
+		sync_dirty_buffer(bh);
 	brelse(bh);
 fail:
 	gfs2_quota_cleanup(sdp);