f2fs: add a rw_sem to cover quota flag changes

Two paths to update quota and f2fs_lock_op:

1.
 - lock_op
 |  - quota_update
 `- unlock_op

2.
 - quota_update
 - lock_op
 `- unlock_op

But, we need to make a transaction on quota_update + lock_op in #2 case.
So, this patch introduces:
1. lock_op
2. down_write
3. check __need_flush
4. up_write
5. if there is dirty quota entries, flush them
6. otherwise, good to go

Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/checkpoint.c

@@ -1133,17 +1133,24 @@ static void __prepare_cp_block(struct f2fs_sb_info *sbi)
 
 static bool __need_flush_quota(struct f2fs_sb_info *sbi)
 {
+	bool ret = false;
+
 	if (!is_journalled_quota(sbi))
 		return false;
-	if (is_sbi_flag_set(sbi, SBI_QUOTA_SKIP_FLUSH))
-		return false;
-	if (is_sbi_flag_set(sbi, SBI_QUOTA_NEED_REPAIR))
-		return false;
-	if (is_sbi_flag_set(sbi, SBI_QUOTA_NEED_FLUSH))
-		return true;
-	if (get_pages(sbi, F2FS_DIRTY_QDATA))
-		return true;
-	return false;
+
+	down_write(&sbi->quota_sem);
+	if (is_sbi_flag_set(sbi, SBI_QUOTA_SKIP_FLUSH)) {
+		ret = false;
+	} else if (is_sbi_flag_set(sbi, SBI_QUOTA_NEED_REPAIR)) {
+		ret = false;
+	} else if (is_sbi_flag_set(sbi, SBI_QUOTA_NEED_FLUSH)) {
+		clear_sbi_flag(sbi, SBI_QUOTA_NEED_FLUSH);
+		ret = true;
+	} else if (get_pages(sbi, F2FS_DIRTY_QDATA)) {
+		ret = true;
+	}
+	up_write(&sbi->quota_sem);
+	return ret;
 }
 
 /*
@@ -1162,26 +1169,22 @@ static int block_operations(struct f2fs_sb_info *sbi)
 	blk_start_plug(&plug);
 
 retry_flush_quotas:
+	f2fs_lock_all(sbi);
 	if (__need_flush_quota(sbi)) {
 		int locked;
 
 		if (++cnt > DEFAULT_RETRY_QUOTA_FLUSH_COUNT) {
 			set_sbi_flag(sbi, SBI_QUOTA_SKIP_FLUSH);
-			f2fs_lock_all(sbi);
+			set_sbi_flag(sbi, SBI_QUOTA_NEED_FLUSH);
 			goto retry_flush_dents;
 		}
-		clear_sbi_flag(sbi, SBI_QUOTA_NEED_FLUSH);
+		f2fs_unlock_all(sbi);
 
 		/* only failed during mount/umount/freeze/quotactl */
 		locked = down_read_trylock(&sbi->sb->s_umount);
 		f2fs_quota_sync(sbi->sb, -1);
 		if (locked)
 			up_read(&sbi->sb->s_umount);
-	}
-
-	f2fs_lock_all(sbi);
-	if (__need_flush_quota(sbi)) {
-		f2fs_unlock_all(sbi);
 		cond_resched();
 		goto retry_flush_quotas;
 	}
@@ -1203,12 +1206,6 @@ retry_flush_dents:
 	 */
 	down_write(&sbi->node_change);
 
-	if (__need_flush_quota(sbi)) {
-		up_write(&sbi->node_change);
-		f2fs_unlock_all(sbi);
-		goto retry_flush_quotas;
-	}
-
 	if (get_pages(sbi, F2FS_DIRTY_IMETA)) {
 		up_write(&sbi->node_change);
 		f2fs_unlock_all(sbi);

fs/f2fs/f2fs.h

@@ -1256,6 +1256,7 @@ struct f2fs_sb_info {
 	block_t unusable_block_count;		/* # of blocks saved by last cp */
 
 	unsigned int nquota_files;		/* # of quota sysfile */
+	struct rw_semaphore quota_sem;		/* blocking cp for flags */
 
 	/* # of pages, see count_type */
 	atomic_t nr_pages[NR_COUNT_TYPE];

fs/f2fs/super.c

@@ -1919,6 +1919,18 @@ int f2fs_quota_sync(struct super_block *sb, int type)
 	int cnt;
 	int ret;
 
+	/*
+	 * do_quotactl
+	 *  f2fs_quota_sync
+	 *  down_read(quota_sem)
+	 *  dquot_writeback_dquots()
+	 *  f2fs_dquot_commit
+	 *                            block_operation
+	 *                            down_read(quota_sem)
+	 */
+	f2fs_lock_op(sbi);
+
+	down_read(&sbi->quota_sem);
 	ret = dquot_writeback_dquots(sb, type);
 	if (ret)
 		goto out;
@@ -1956,6 +1968,8 @@ int f2fs_quota_sync(struct super_block *sb, int type)
 out:
 	if (ret)
 		set_sbi_flag(F2FS_SB(sb), SBI_QUOTA_NEED_REPAIR);
+	up_read(&sbi->quota_sem);
+	f2fs_unlock_op(sbi);
 	return ret;
 }
 
@@ -2047,32 +2061,40 @@ static void f2fs_truncate_quota_inode_pages(struct super_block *sb)
 
 static int f2fs_dquot_commit(struct dquot *dquot)
 {
+	struct f2fs_sb_info *sbi = F2FS_SB(dquot->dq_sb);
 	int ret;
 
+	down_read(&sbi->quota_sem);
 	ret = dquot_commit(dquot);
 	if (ret < 0)
-		set_sbi_flag(F2FS_SB(dquot->dq_sb), SBI_QUOTA_NEED_REPAIR);
+		set_sbi_flag(sbi, SBI_QUOTA_NEED_REPAIR);
+	up_read(&sbi->quota_sem);
 	return ret;
 }
 
 static int f2fs_dquot_acquire(struct dquot *dquot)
 {
+	struct f2fs_sb_info *sbi = F2FS_SB(dquot->dq_sb);
 	int ret;
 
+	down_read(&sbi->quota_sem);
 	ret = dquot_acquire(dquot);
 	if (ret < 0)
-		set_sbi_flag(F2FS_SB(dquot->dq_sb), SBI_QUOTA_NEED_REPAIR);
-
+		set_sbi_flag(sbi, SBI_QUOTA_NEED_REPAIR);
+	up_read(&sbi->quota_sem);
 	return ret;
 }
 
 static int f2fs_dquot_release(struct dquot *dquot)
 {
+	struct f2fs_sb_info *sbi = F2FS_SB(dquot->dq_sb);
 	int ret;
 
+	down_read(&sbi->quota_sem);
 	ret = dquot_release(dquot);
 	if (ret < 0)
-		set_sbi_flag(F2FS_SB(dquot->dq_sb), SBI_QUOTA_NEED_REPAIR);
+		set_sbi_flag(sbi, SBI_QUOTA_NEED_REPAIR);
+	up_read(&sbi->quota_sem);
 	return ret;
 }
 
@@ -2082,22 +2104,27 @@ static int f2fs_dquot_mark_dquot_dirty(struct dquot *dquot)
 	struct f2fs_sb_info *sbi = F2FS_SB(sb);
 	int ret;
 
+	down_read(&sbi->quota_sem);
 	ret = dquot_mark_dquot_dirty(dquot);
 
 	/* if we are using journalled quota */
 	if (is_journalled_quota(sbi))
 		set_sbi_flag(sbi, SBI_QUOTA_NEED_FLUSH);
 
+	up_read(&sbi->quota_sem);
 	return ret;
 }
 
 static int f2fs_dquot_commit_info(struct super_block *sb, int type)
 {
+	struct f2fs_sb_info *sbi = F2FS_SB(sb);
 	int ret;
 
+	down_read(&sbi->quota_sem);
 	ret = dquot_commit_info(sb, type);
 	if (ret < 0)
-		set_sbi_flag(F2FS_SB(sb), SBI_QUOTA_NEED_REPAIR);
+		set_sbi_flag(sbi, SBI_QUOTA_NEED_REPAIR);
+	up_read(&sbi->quota_sem);
 	return ret;
 }
 
@@ -3167,6 +3194,7 @@ try_onemore:
 	}
 
 	init_rwsem(&sbi->cp_rwsem);
+	init_rwsem(&sbi->quota_sem);
 	init_waitqueue_head(&sbi->cp_wait);
 	init_sb_info(sbi);