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

[Jan Kara <jack@suse.cz>]

On Tue 25-05-21 13:48:05, Darrick J. Wong wrote:
> 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);

OK, and filemap_invalidate_lock_shared() for down_read()? I guess that
works for me.

								Honza

 
> 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
> > 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR