Re: [PATCH] fs: create kiocb_{start,end}_write() helpers

[Jens Axboe <axboe@kernel.dk>]

On 8/15/23 10:57 AM, Amir Goldstein wrote:
> +/**
> + * kiocb_start_write - get write access to a superblock for async file io
> + * @iocb: the io context we want to submit the write with
> + *
> + * This is a variant of file_start_write() for async io submission.
> + * Should be matched with a call to kiocb_end_write().
> + */
> +static inline void kiocb_start_write(struct kiocb *iocb)
> +{
> +	struct inode *inode = file_inode(iocb->ki_filp);
> +
> +	iocb->ki_flags |= IOCB_WRITE;
> +	if (WARN_ON_ONCE(iocb->ki_flags & IOCB_WRITE_STARTED))
> +		return;
> +	if (!S_ISREG(inode->i_mode))
> +		return;
> +	sb_start_write(inode->i_sb);
> +	/*
> +	 * Fool lockdep by telling it the lock got released so that it
> +	 * doesn't complain about the held lock when we return to userspace.
> +	 */
> +	__sb_writers_release(inode->i_sb, SB_FREEZE_WRITE);
> +	iocb->ki_flags |= IOCB_WRITE_STARTED;
> +}
> +
> +/**
> + * kiocb_end_write - drop write access to a superblock after async file io
> + * @iocb: the io context we sumbitted the write with
> + *
> + * Should be matched with a call to kiocb_start_write().
> + */
> +static inline void kiocb_end_write(struct kiocb *iocb)
> +{
> +	struct inode *inode = file_inode(iocb->ki_filp);
> +
> +	if (!(iocb->ki_flags & IOCB_WRITE_STARTED))
> +		return;
> +	if (!S_ISREG(inode->i_mode))
> +		return;
> +	/*
> +	 * Tell lockdep we inherited freeze protection from submission thread.
> +	 */
> +	__sb_writers_acquired(inode->i_sb, SB_FREEZE_WRITE);
> +	sb_end_write(inode->i_sb);
> +	iocb->ki_flags &= ~IOCB_WRITE_STARTED;
>  }

Please don't add code that dips into the inode when it's not needed for
all callers.

-- 
Jens Axboe