It seems you need to remove dummy f2fs_quota_sync() in fs/f2fs/super.c to
fix the build error.

3204 int f2fs_quota_sync(struct super_block *sb, int type)
3205 {       
3206         return 0;
3207 }  

On 02/07, Chao Yu wrote:
> F2FS-fs (dm-59): checkpoint=enable has some unwritten data.
> 
> ------------[ cut here ]------------
> WARNING: CPU: 6 PID: 8013 at fs/quota/dquot.c:691 
> dquot_writeback_dquots+0x2fc/0x308
> pc : dquot_writeback_dquots+0x2fc/0x308
> lr : f2fs_quota_sync+0xcc/0x1c4
> Call trace:
> dquot_writeback_dquots+0x2fc/0x308
> f2fs_quota_sync+0xcc/0x1c4
> f2fs_write_checkpoint+0x3d4/0x9b0
> f2fs_issue_checkpoint+0x1bc/0x2c0
> f2fs_sync_fs+0x54/0x150
> f2fs_do_sync_file+0x2f8/0x814
> __f2fs_ioctl+0x1960/0x3244
> f2fs_ioctl+0x54/0xe0
> __arm64_sys_ioctl+0xa8/0xe4
> invoke_syscall+0x58/0x114
> 
> checkpoint and f2fs_remount may race as below, resulting triggering warning
> in dquot_writeback_dquots().
> 
> atomic write                                    remount
>                                                 - do_remount
>                                                  - down_write(&sb->s_umount);
>                                                   - f2fs_remount
> - ioctl
>  - f2fs_do_sync_file
>   - f2fs_sync_fs
>    - f2fs_write_checkpoint
>     - block_operations
>      - locked = down_read_trylock(&sbi->sb->s_umount)
>        : fail to lock due to the write lock was held by remount
>                                                  - up_write(&sb->s_umount);
>      - f2fs_quota_sync
>       - dquot_writeback_dquots
>        - WARN_ON_ONCE(!rwsem_is_locked(&sb->s_umount))
>        : trigger warning because s_umount lock was unlocked by remount
> 
> If checkpoint comes from mount/umount/remount/freeze/quotactl, caller of
> checkpoint has already held s_umount lock, calling dquot_writeback_dquots()
> in the context should be safe.
> 
> So let's record task to sbi->umount_lock_holder, so that checkpoint can
> know whether the lock has held in the context or not by checking current
> w/ it.
> 
> In addition, in order to not misrepresent caller of checkpoint, we should
> not allow to trigger async checkpoint for those callers: mount/umount/remount/
> freeze/quotactl.
> 
> Fixes: af033b2aa8a8 ("f2fs: guarantee journalled quota data by checkpoint")
> Signed-off-by: Chao Yu <c...@kernel.org>
> ---
> v2:
> - fix to return correct error number in f2fs_quota_on()
> - clean up codes in block_operations()
> - fix commit message
>  fs/f2fs/checkpoint.c | 15 ++++++-----
>  fs/f2fs/f2fs.h       |  3 ++-
>  fs/f2fs/super.c      | 63 ++++++++++++++++++++++++++++++++++----------
>  3 files changed, 60 insertions(+), 21 deletions(-)
> 
> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
> index efda9a022981..bd890738b94d 100644
> --- a/fs/f2fs/checkpoint.c
> +++ b/fs/f2fs/checkpoint.c
> @@ -1237,7 +1237,7 @@ static int block_operations(struct f2fs_sb_info *sbi)
>  retry_flush_quotas:
>       f2fs_lock_all(sbi);
>       if (__need_flush_quota(sbi)) {
> -             int locked;
> +             bool need_lock = sbi->umount_lock_holder != current;
>  
>               if (++cnt > DEFAULT_RETRY_QUOTA_FLUSH_COUNT) {
>                       set_sbi_flag(sbi, SBI_QUOTA_SKIP_FLUSH);
> @@ -1246,11 +1246,13 @@ static int block_operations(struct f2fs_sb_info *sbi)
>               }
>               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)
> +             /* don't grab s_umount lock during 
> mount/umount/remount/freeze/quotactl */
> +             if (!need_lock) {
> +                     f2fs_do_quota_sync(sbi->sb, -1);
> +             } else if (down_read_trylock(&sbi->sb->s_umount)) {
> +                     f2fs_do_quota_sync(sbi->sb, -1);
>                       up_read(&sbi->sb->s_umount);
> +             }
>               cond_resched();
>               goto retry_flush_quotas;
>       }
> @@ -1867,7 +1869,8 @@ int f2fs_issue_checkpoint(struct f2fs_sb_info *sbi)
>       struct cp_control cpc;
>  
>       cpc.reason = __get_cp_reason(sbi);
> -     if (!test_opt(sbi, MERGE_CHECKPOINT) || cpc.reason != CP_SYNC) {
> +     if (!test_opt(sbi, MERGE_CHECKPOINT) || cpc.reason != CP_SYNC ||
> +             sbi->umount_lock_holder == current) {
>               int ret;
>  
>               f2fs_down_write(&sbi->gc_lock);
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index bd0d8138b71d..205bdcbd01e6 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -1668,6 +1668,7 @@ struct f2fs_sb_info {
>  
>       unsigned int nquota_files;              /* # of quota sysfile */
>       struct f2fs_rwsem quota_sem;            /* blocking cp for flags */
> +     struct task_struct *umount_lock_holder; /* s_umount lock holder */
>  
>       /* # of pages, see count_type */
>       atomic_t nr_pages[NR_COUNT_TYPE];
> @@ -3633,7 +3634,7 @@ int f2fs_inode_dirtied(struct inode *inode, bool sync);
>  void f2fs_inode_synced(struct inode *inode);
>  int f2fs_dquot_initialize(struct inode *inode);
>  int f2fs_enable_quota_files(struct f2fs_sb_info *sbi, bool rdonly);
> -int f2fs_quota_sync(struct super_block *sb, int type);
> +int f2fs_do_quota_sync(struct super_block *sb, int type);
>  loff_t max_file_blocks(struct inode *inode);
>  void f2fs_quota_off_umount(struct super_block *sb);
>  void f2fs_save_errors(struct f2fs_sb_info *sbi, unsigned char flag);
> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> index 24ded06c8980..944b09fd3aca 100644
> --- a/fs/f2fs/super.c
> +++ b/fs/f2fs/super.c
> @@ -1738,22 +1738,28 @@ int f2fs_sync_fs(struct super_block *sb, int sync)
>  
>  static int f2fs_freeze(struct super_block *sb)
>  {
> +     struct f2fs_sb_info *sbi = F2FS_SB(sb);
> +
>       if (f2fs_readonly(sb))
>               return 0;
>  
>       /* IO error happened before */
> -     if (unlikely(f2fs_cp_error(F2FS_SB(sb))))
> +     if (unlikely(f2fs_cp_error(sbi)))
>               return -EIO;
>  
>       /* must be clean, since sync_filesystem() was already called */
> -     if (is_sbi_flag_set(F2FS_SB(sb), SBI_IS_DIRTY))
> +     if (is_sbi_flag_set(sbi, SBI_IS_DIRTY))
>               return -EINVAL;
>  
> +     sbi->umount_lock_holder = current;
> +
>       /* Let's flush checkpoints and stop the thread. */
> -     f2fs_flush_ckpt_thread(F2FS_SB(sb));
> +     f2fs_flush_ckpt_thread(sbi);
> +
> +     sbi->umount_lock_holder = NULL;
>  
>       /* to avoid deadlock on f2fs_evict_inode->SB_FREEZE_FS */
> -     set_sbi_flag(F2FS_SB(sb), SBI_IS_FREEZING);
> +     set_sbi_flag(sbi, SBI_IS_FREEZING);
>       return 0;
>  }
>  
> @@ -2330,6 +2336,8 @@ static int f2fs_remount(struct super_block *sb, int 
> *flags, char *data)
>       org_mount_opt = sbi->mount_opt;
>       old_sb_flags = sb->s_flags;
>  
> +     sbi->umount_lock_holder = current;
> +
>  #ifdef CONFIG_QUOTA
>       org_mount_opt.s_jquota_fmt = F2FS_OPTION(sbi).s_jquota_fmt;
>       for (i = 0; i < MAXQUOTAS; i++) {
> @@ -2553,6 +2561,8 @@ static int f2fs_remount(struct super_block *sb, int 
> *flags, char *data)
>  
>       limit_reserve_root(sbi);
>       *flags = (*flags & ~SB_LAZYTIME) | (sb->s_flags & SB_LAZYTIME);
> +
> +     sbi->umount_lock_holder = NULL;
>       return 0;
>  restore_checkpoint:
>       if (need_enable_checkpoint) {
> @@ -2593,6 +2603,8 @@ static int f2fs_remount(struct super_block *sb, int 
> *flags, char *data)
>  #endif
>       sbi->mount_opt = org_mount_opt;
>       sb->s_flags = old_sb_flags;
> +
> +     sbi->umount_lock_holder = NULL;
>       return err;
>  }
>  
> @@ -2909,7 +2921,7 @@ static int f2fs_quota_sync_file(struct f2fs_sb_info 
> *sbi, int type)
>       return ret;
>  }
>  
> -int f2fs_quota_sync(struct super_block *sb, int type)
> +int f2fs_do_quota_sync(struct super_block *sb, int type)
>  {
>       struct f2fs_sb_info *sbi = F2FS_SB(sb);
>       struct quota_info *dqopt = sb_dqopt(sb);
> @@ -2957,11 +2969,21 @@ int f2fs_quota_sync(struct super_block *sb, int type)
>       return ret;
>  }
>  
> +static int f2fs_quota_sync(struct super_block *sb, int type)
> +{
> +     int ret;
> +
> +     F2FS_SB(sb)->umount_lock_holder = current;
> +     ret = f2fs_do_quota_sync(sb, type);
> +     F2FS_SB(sb)->umount_lock_holder = NULL;
> +     return ret;
> +}
> +
>  static int f2fs_quota_on(struct super_block *sb, int type, int format_id,
>                                                       const struct path *path)
>  {
>       struct inode *inode;
> -     int err;
> +     int err = 0;
>  
>       /* if quota sysfile exists, deny enabling quota with specific file */
>       if (f2fs_sb_has_quota_ino(F2FS_SB(sb))) {
> @@ -2972,31 +2994,34 @@ static int f2fs_quota_on(struct super_block *sb, int 
> type, int format_id,
>       if (path->dentry->d_sb != sb)
>               return -EXDEV;
>  
> -     err = f2fs_quota_sync(sb, type);
> +     F2FS_SB(sb)->umount_lock_holder = current;
> +
> +     err = f2fs_do_quota_sync(sb, type);
>       if (err)
> -             return err;
> +             goto out;
>  
>       inode = d_inode(path->dentry);
>  
>       err = filemap_fdatawrite(inode->i_mapping);
>       if (err)
> -             return err;
> +             goto out;
>  
>       err = filemap_fdatawait(inode->i_mapping);
>       if (err)
> -             return err;
> +             goto out;
>  
>       err = dquot_quota_on(sb, type, format_id, path);
>       if (err)
> -             return err;
> +             goto out;
>  
>       inode_lock(inode);
>       F2FS_I(inode)->i_flags |= F2FS_QUOTA_DEFAULT_FL;
>       f2fs_set_inode_flags(inode);
>       inode_unlock(inode);
>       f2fs_mark_inode_dirty_sync(inode, false);
> -
> -     return 0;
> +out:
> +     F2FS_SB(sb)->umount_lock_holder = NULL;
> +     return err;
>  }
>  
>  static int __f2fs_quota_off(struct super_block *sb, int type)
> @@ -3007,7 +3032,7 @@ static int __f2fs_quota_off(struct super_block *sb, int 
> type)
>       if (!inode || !igrab(inode))
>               return dquot_quota_off(sb, type);
>  
> -     err = f2fs_quota_sync(sb, type);
> +     err = f2fs_do_quota_sync(sb, type);
>       if (err)
>               goto out_put;
>  
> @@ -3030,6 +3055,8 @@ static int f2fs_quota_off(struct super_block *sb, int 
> type)
>       struct f2fs_sb_info *sbi = F2FS_SB(sb);
>       int err;
>  
> +     F2FS_SB(sb)->umount_lock_holder = current;
> +
>       err = __f2fs_quota_off(sb, type);
>  
>       /*
> @@ -3039,6 +3066,9 @@ static int f2fs_quota_off(struct super_block *sb, int 
> type)
>        */
>       if (is_journalled_quota(sbi))
>               set_sbi_flag(sbi, SBI_QUOTA_NEED_REPAIR);
> +
> +     F2FS_SB(sb)->umount_lock_holder = NULL;
> +
>       return err;
>  }
>  
> @@ -4704,6 +4734,7 @@ static int f2fs_fill_super(struct super_block *sb, void 
> *data, int silent)
>       if (err)
>               goto free_compress_inode;
>  
> +     sbi->umount_lock_holder = current;
>  #ifdef CONFIG_QUOTA
>       /* Enable quota usage during mount */
>       if (f2fs_sb_has_quota_ino(sbi) && !f2fs_readonly(sb)) {
> @@ -4830,6 +4861,8 @@ static int f2fs_fill_super(struct super_block *sb, void 
> *data, int silent)
>       f2fs_update_time(sbi, CP_TIME);
>       f2fs_update_time(sbi, REQ_TIME);
>       clear_sbi_flag(sbi, SBI_CP_DISABLED_QUICK);
> +
> +     sbi->umount_lock_holder = NULL;
>       return 0;
>  
>  sync_free_meta:
> @@ -4932,6 +4965,8 @@ static void kill_f2fs_super(struct super_block *sb)
>       struct f2fs_sb_info *sbi = F2FS_SB(sb);
>  
>       if (sb->s_root) {
> +             sbi->umount_lock_holder = current;
> +
>               set_sbi_flag(sbi, SBI_IS_CLOSE);
>               f2fs_stop_gc_thread(sbi);
>               f2fs_stop_discard_thread(sbi);
> -- 
> 2.48.1.502.g6dc24dfdaf-goog


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