Re: [PATCH 2/2] mm: Make swap_readpage() for SWP_FS_OPS use ->direct_IO() not ->readpage()

[David Howells]

David Howells <dhowells@xxxxxxxxxx> wrote:

> Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
> 
> > After submitting the IO here ...
> > 
> > > +	if (ret != -EIOCBQUEUED)
> > > +		swapfile_read_complete(&ki->iocb, ret, 0);
> > 
> > We only touch the 'ki' here ... if the caller didn't call read_complete
> > 
> > > +	swapfile_put_kiocb(ki);
> > 
> > Except for here, which is only touched in order to put the refcount.
> > 
> > So why can't swapfile_read_complete() do the work of freeing the ki?
> 
> When I was doing something similar for cachefiles, I couldn't get it to work
> like that.  I'll have another look at that.

Ah, yes.  generic_file_direct_write() accesses in the kiocb *after* calling
->direct_IO(), so the kiocb *must not* go away until after
generic_file_direct_write() has returned.

David