Re: [PATCH v2 3/4] fs: add check functions for sb_start_{write,pagefault,intwrite}

[Dave Chinner <david@fromorbit.com>]

On Wed, Mar 16, 2022 at 10:22:39PM +0900, Naohiro Aota wrote:
> Add a function sb_write_started() to return if sb_start_write() is
> properly called. It is used in the next commit.
> 
> Also, add the similar functions for sb_start_pagefault() and
> sb_start_intwrite().
> 
> Reviewed-by: Filipe Manana <fdmanana@suse.com>
> Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
> ---
>  include/linux/fs.h | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 27746a3da8fd..0c8714d64169 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1732,6 +1732,11 @@ static inline bool __sb_start_write_trylock(struct super_block *sb, int level)
>  #define __sb_writers_release(sb, lev)	\
>  	percpu_rwsem_release(&(sb)->s_writers.rw_sem[(lev)-1], 1, _THIS_IP_)
>  
> +static inline bool __sb_write_started(struct super_block *sb, int level)
> +{
> +	return lockdep_is_held_type(sb->s_writers.rw_sem + level - 1, 1);
> +}
> +
>  /**
>   * sb_end_write - drop write access to a superblock
>   * @sb: the super we wrote to
> @@ -1797,6 +1802,11 @@ static inline bool sb_start_write_trylock(struct super_block *sb)
>  	return __sb_start_write_trylock(sb, SB_FREEZE_WRITE);
>  }
>  
> +static inline bool sb_write_started(struct super_block *sb)
> +{
> +	return __sb_write_started(sb, SB_FREEZE_WRITE);
> +}
> +
>  /**
>   * sb_start_pagefault - get write access to a superblock from a page fault
>   * @sb: the super we write to
> @@ -1821,6 +1831,11 @@ static inline void sb_start_pagefault(struct super_block *sb)
>  	__sb_start_write(sb, SB_FREEZE_PAGEFAULT);
>  }
>  
> +static inline bool sb_pagefault_started(struct super_block *sb)
> +{
> +	return __sb_write_started(sb, SB_FREEZE_PAGEFAULT);
> +}
> +
>  /**
>   * sb_start_intwrite - get write access to a superblock for internal fs purposes
>   * @sb: the super we write to
> @@ -1844,6 +1859,11 @@ static inline bool sb_start_intwrite_trylock(struct super_block *sb)
>  	return __sb_start_write_trylock(sb, SB_FREEZE_FS);
>  }
>  
> +static inline bool sb_intwrite_started(struct super_block *sb)
> +{
> +	return __sb_write_started(sb, SB_FREEZE_FS);
> +}
> +
>  bool inode_owner_or_capable(struct user_namespace *mnt_userns,
>  			    const struct inode *inode);
>  

We should not be adding completely unused code to the VFS APIs.

Just rename __sb_write_started() to sb_write_started() and pass
SB_FREEZE_WRITE directly from the single debug assert that you've
added that needs this check.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com