quota: Fix possible corruption of dqi_flags

dqi_flags modifications are protected by dq_data_lock. However the
modifications in vfs_load_quota_inode() and in mark_info_dirty() were
not which could lead to corruption of dqi_flags. Since modifications to
dqi_flags are rare, this is hard to observe in practice but in theory it
could happen. Fix the problem by always using dq_data_lock for
protection.
Signed-off-by: Jan Kara <jack@suse.cz>

fs/quota/dquot.c

@@ -389,7 +389,9 @@ static inline int clear_dquot_dirty(struct dquot *dquot)
 
 void mark_info_dirty(struct super_block *sb, int type)
 {
-	set_bit(DQF_INFO_DIRTY_B, &sb_dqopt(sb)->info[type].dqi_flags);
+	spin_lock(&dq_data_lock);
+	sb_dqopt(sb)->info[type].dqi_flags |= DQF_INFO_DIRTY;
+	spin_unlock(&dq_data_lock);
 }
 EXPORT_SYMBOL(mark_info_dirty);
 
@@ -2316,8 +2318,11 @@ static int vfs_load_quota_inode(struct inode *inode, int type, int format_id,
 	error = dqopt->ops[type]->read_file_info(sb, type);
 	if (error < 0)
 		goto out_file_init;
-	if (dqopt->flags & DQUOT_QUOTA_SYS_FILE)
+	if (dqopt->flags & DQUOT_QUOTA_SYS_FILE) {
+		spin_lock(&dq_data_lock);
 		dqopt->info[type].dqi_flags |= DQF_SYS_FILE;
+		spin_unlock(&dq_data_lock);
+	}
 	spin_lock(&dq_state_lock);
 	dqopt->flags |= dquot_state_flag(flags, type);
 	spin_unlock(&dq_state_lock);

fs/quota/quota_v1.c

@@ -189,7 +189,6 @@ static int v1_write_file_info(struct super_block *sb, int type)
 	int ret;
 
 	down_write(&dqopt->dqio_sem);
-	dqopt->info[type].dqi_flags &= ~DQF_INFO_DIRTY;
 	ret = sb->s_op->quota_read(sb, type, (char *)&dqblk,
 				sizeof(struct v1_disk_dqblk), v1_dqoff(0));
 	if (ret != sizeof(struct v1_disk_dqblk)) {
@@ -197,8 +196,11 @@ static int v1_write_file_info(struct super_block *sb, int type)
 			ret = -EIO;
 		goto out;
 	}
+	spin_lock(&dq_data_lock);
+	dqopt->info[type].dqi_flags &= ~DQF_INFO_DIRTY;
 	dqblk.dqb_itime = dqopt->info[type].dqi_igrace;
 	dqblk.dqb_btime = dqopt->info[type].dqi_bgrace;
+	spin_unlock(&dq_data_lock);
 	ret = sb->s_op->quota_write(sb, type, (char *)&dqblk,
 	      sizeof(struct v1_disk_dqblk), v1_dqoff(0));
 	if (ret == sizeof(struct v1_disk_dqblk))