Re: [PATCH 04/14] mm: Add functions to lock invalidate_lock for two mappings

Darrick J. Wong
2021-06-07T15:46:24Z

On Mon, Jun 07, 2021 at 04:52:14PM +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>

Straightforward lift from xfs, though now with vfs lock ordering
rules...

Reviewed-by: Darrick J. Wong <djwong@kernel.org>

--D

> ---
> 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 d8afbc9661d7..ddc11bafc183 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -849,6 +849,12 @@ static inline void filemap_invalidate_unlock_shared(
> void lock_two_nondirectories(struct inode *, struct inode*);
> void unlock_two_nondirectories(struct inode *, struct inode*);
>
> +void filemap_invalidate_lock_two(struct address_space *mapping1,
> + struct address_space *mapping2);
> +void filemap_invalidate_unlock_two(struct address_space *mapping1,
> + 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 c8e7e451d81e..b8e9bccecd9f 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_lock_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_lock_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_lock_two);
> +
> +/*
> + * filemap_invalidate_unlock_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_unlock_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_unlock_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
>