Re: i_mutex locking in generic_file_splice_write()

[Jens Axboe <jens.axboe@oracle.com>]

On Fri, Oct 13 2006, Mark Fasheh wrote:
>  /*
> + * We rarely want to lock two inodes that do not have a parent/child
> + * relationship (such as directory, child inode) simultaneously. The
> + * vast majority of file systems should be able to get along fine
> + * without this. Do not use these functions except as a last resort.
> + */
> +static inline void inode_double_lock(struct inode *inode1, struct inode *inode2)
> +{
> +	if (!inode2) {
> +		mutex_lock(&inode1->i_mutex);
> +		return;
> +	}
> +
> +	if (inode1 < inode2) {
> +		mutex_lock_nested(&inode1->i_mutex, I_MUTEX_PARENT);
> +		mutex_lock_nested(&inode2->i_mutex, I_MUTEX_CHILD);
> +	} else {
> +		mutex_lock_nested(&inode2->i_mutex, I_MUTEX_PARENT);
> +		mutex_lock_nested(&inode1->i_mutex, I_MUTEX_CHILD);
> +	}
> +}

This wont fly, it's completely tailored to splice in that one one inode
can be NULL. It also requires the 2nd inode to be that potentially NULL
pointer.

The function should work for any of the inodes to be NULL, if exported
as a helper.


-- 
Jens Axboe