Re: [PATCH 04/13] mm: Add functions to lock invalidate_lock for two mappings

["Darrick J. Wong" <djwong@kernel.org>]

On Tue, May 25, 2021 at 03:50:41PM +0200, Jan Kara wrote:
> Some operations such as reflinking blocks among files will need to lock
> invalidate_lock for two mappings. Add helper functions to do that.
> 
> Signed-off-by: Jan Kara <jack@suse.cz>
> ---
>  include/linux/fs.h |  6 ++++++
>  mm/filemap.c       | 38 ++++++++++++++++++++++++++++++++++++++
>  2 files changed, 44 insertions(+)
> 
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 897238d9f1e0..e6f7447505f5 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -822,6 +822,12 @@ static inline void inode_lock_shared_nested(struct inode *inode, unsigned subcla
>  void lock_two_nondirectories(struct inode *, struct inode*);
>  void unlock_two_nondirectories(struct inode *, struct inode*);
>  
> +void filemap_invalidate_down_write_two(struct address_space *mapping1,
> +				       struct address_space *mapping2);
> +void filemap_invalidate_up_write_two(struct address_space *mapping1,

TBH I find myself wishing that the invalidate_lock used the same
lock/unlock style wrappers that we use for i_rwsem.

filemap_invalidate_lock(inode1->mapping);
filemap_invalidate_lock_two(inode1->i_mapping, inode2->i_mapping);

To be fair, I've never been able to keep straight that down means lock
and up means unlock.  Ah well, at least you didn't use "p" and "v".

Mechanically, the changes look ok to me.
Acked-by: Darrick J. Wong <djwong@kernel.org>

--D

> +				     struct address_space *mapping2);
> +
> +
>  /*
>   * NOTE: in a 32bit arch with a preemptable kernel and
>   * an UP compile the i_size_read/write must be atomic
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 4d9ec4c6cc34..d3801a9739aa 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -1009,6 +1009,44 @@ struct page *__page_cache_alloc(gfp_t gfp)
>  EXPORT_SYMBOL(__page_cache_alloc);
>  #endif
>  
> +/*
> + * filemap_invalidate_down_write_two - lock invalidate_lock for two mappings
> + *
> + * Lock exclusively invalidate_lock of any passed mapping that is not NULL.
> + *
> + * @mapping1: the first mapping to lock
> + * @mapping2: the second mapping to lock
> + */
> +void filemap_invalidate_down_write_two(struct address_space *mapping1,
> +				       struct address_space *mapping2)
> +{
> +	if (mapping1 > mapping2)
> +		swap(mapping1, mapping2);
> +	if (mapping1)
> +		down_write(&mapping1->invalidate_lock);
> +	if (mapping2 && mapping1 != mapping2)
> +		down_write_nested(&mapping2->invalidate_lock, 1);
> +}
> +EXPORT_SYMBOL(filemap_invalidate_down_write_two);
> +
> +/*
> + * filemap_invalidate_up_write_two - unlock invalidate_lock for two mappings
> + *
> + * Unlock exclusive invalidate_lock of any passed mapping that is not NULL.
> + *
> + * @mapping1: the first mapping to unlock
> + * @mapping2: the second mapping to unlock
> + */
> +void filemap_invalidate_up_write_two(struct address_space *mapping1,
> +				     struct address_space *mapping2)
> +{
> +	if (mapping1)
> +		up_write(&mapping1->invalidate_lock);
> +	if (mapping2 && mapping1 != mapping2)
> +		up_write(&mapping2->invalidate_lock);
> +}
> +EXPORT_SYMBOL(filemap_invalidate_up_write_two);
> +
>  /*
>   * In order to wait for pages to become available there must be
>   * waitqueues associated with pages. By using a hash table of
> -- 
> 2.26.2
>