Re: [PATCH] iomap: Return zero in case of unsuccessful pagecache invalidation before DIO

[Goldwyn Rodrigues <rgoldwyn@suse.de>]

On 17:23 28/05, Darrick J. Wong wrote:
> On Thu, May 28, 2020 at 02:21:03PM -0500, Goldwyn Rodrigues wrote:
> > 
> > Filesystems such as btrfs are unable to guarantee page invalidation
> > because pages could be locked as a part of the extent. Return zero
> 
> Locked for what?  filemap_write_and_wait_range should have just cleaned
> them off.
> 
> > in case a page cache invalidation is unsuccessful so filesystems can
> > fallback to buffered I/O. This is similar to
> > generic_file_direct_write().
> > 
> > This takes care of the following invalidation warning during btrfs
> > mixed buffered and direct I/O using iomap_dio_rw():
> > 
> > Page cache invalidation failure on direct I/O.  Possible data
> > corruption due to collision with buffered I/O!
> > 
> > Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
> > 
> > diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> > index e4addfc58107..215315be6233 100644
> > --- a/fs/iomap/direct-io.c
> > +++ b/fs/iomap/direct-io.c
> > @@ -483,9 +483,15 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
> >  	 */
> >  	ret = invalidate_inode_pages2_range(mapping,
> >  			pos >> PAGE_SHIFT, end >> PAGE_SHIFT);
> > -	if (ret)
> > -		dio_warn_stale_pagecache(iocb->ki_filp);
> > -	ret = 0;
> > +	/*
> > +	 * If a page can not be invalidated, return 0 to fall back
> > +	 * to buffered write.
> > +	 */
> > +	if (ret) {
> > +		if (ret == -EBUSY)
> > +			ret = 0;
> > +		goto out_free_dio;
> 
> XFS doesn't fall back to buffered io when directio fails, which means
> this will cause a regression there.
> 
> Granted mixing write types is bogus...
> 

I have not seen page invalidation failure errors on XFS, but what should
happen hypothetically if they do occur? Carry on with the direct I/O?
Would an error return like -ENOTBLK be better?

-- 
Goldwyn