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Date:   Tue, 4 Jun 2019 11:36:19 -0700
From:   Jaegeuk Kim <jaegeuk@kernel.org>
To:     linux-kernel@vger.kernel.org,
        linux-f2fs-devel@lists.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH v3] f2fs: add a rw_sem to cover quota flag
 changes
Message-ID: <20190604183619.GA8507@jaegeuk-macbookpro.roam.corp.google.com>
References: <20190530033115.16853-1-jaegeuk@kernel.org>
 <20190530175714.GB28719@jaegeuk-macbookpro.roam.corp.google.com>
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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>
---

v3 from v2:
 - refactor to fix quota corruption issue
  : it seems that the previous scenario is not real and no deadlock case was
    encountered.

 fs/f2fs/checkpoint.c | 41 +++++++++++++++++++----------------------
 fs/f2fs/f2fs.h       |  1 +
 fs/f2fs/super.c      | 26 +++++++++++++++++++++-----
 3 files changed, 41 insertions(+), 27 deletions(-)

diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
index 89825261d474..43f65f0962e5 100644
--- a/fs/f2fs/checkpoint.c
+++ b/fs/f2fs/checkpoint.c
@@ -1131,17 +1131,24 @@ 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;
 }
 
 /*
@@ -1160,26 +1167,22 @@ 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;
 	}
@@ -1201,12 +1204,6 @@ static int block_operations(struct f2fs_sb_info *sbi)
 	 */
 	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);
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 9674a85154b2..9bd2bf0f559b 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -1253,6 +1253,7 @@ 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];
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index 15d7e30bfc72..5a318399a2fa 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -1964,6 +1964,7 @@ int f2fs_quota_sync(struct super_block *sb, int type)
 	int cnt;
 	int ret;
 
+	down_read(&sbi->quota_sem);
 	ret = dquot_writeback_dquots(sb, type);
 	if (ret)
 		goto out;
@@ -2001,6 +2002,7 @@ 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);
 	return ret;
 }
 
@@ -2094,32 +2096,40 @@ 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;
 }
 
@@ -2129,22 +2139,27 @@ 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;
 }
 
@@ -3253,6 +3268,7 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
 	}
 
 	init_rwsem(&sbi->cp_rwsem);
+	init_rwsem(&sbi->quota_sem);
 	init_waitqueue_head(&sbi->cp_wait);
 	init_sb_info(sbi);
 
-- 
2.19.0.605.g01d371f741-goog