linux-kernel - Re: [PATCH] fs: make sure to invalidate pages if we fall back on buffered reads

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Message-ID: <20100614131336.GB2322@localhost.localdomain>
Date:	Mon, 14 Jun 2010 09:13:36 -0400
From:	Josef Bacik <josef@...hat.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Josef Bacik <josef@...hat.com>, linux-btrfs@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fs: make sure to invalidate pages if we fall back on
	buffered reads

On Mon, Jun 14, 2010 at 04:17:36AM -0400, Christoph Hellwig wrote:
> On Tue, Jun 08, 2010 at 10:24:04AM -0400, Josef Bacik wrote:
> > Since BTRFS can fallback on buffered reads after having done some direct reads,
> > we need to make sure to invalidate any pages that we may have read by doing
> > buffered IO.  This shouldn't have shown up as a visible user problem, it's just
> > for correctness sake.  Thanks,
> 
> Everything else in direct I/O land uses invalidate_inode_pages2(_range),
> why not this one?
>

In __generic_file_aio_write if we fall back on buffered writes we call
invalidate_mapping_pages to invalidate the buffered range, so I just did that
here, is that acceptable?
 
> >  	loff_t *ppos = &iocb->ki_pos;
> > +	bool invalidate = false;
> >  
> >  	count = 0;
> >  	retval = generic_segment_checks(iov, &nr_segs, &count, VERIFY_WRITE);
> > @@ -1291,7 +1292,8 @@ generic_file_aio_read(struct kiocb *iocb, const struct iovec *iov,
> >  							iov, pos, nr_segs);
> >  			}
> >  			if (retval > 0) {
> > -				*ppos = pos + retval;
> > +				pos += retval;
> > +				*ppos = pos;
> >  				count -= retval;
> >  			}
> >  
> > @@ -1307,6 +1309,7 @@ generic_file_aio_read(struct kiocb *iocb, const struct iovec *iov,
> >  				file_accessed(filp);
> >  				goto out;
> >  			}
> > +			invalidate = true;
> >  		}
> >  	}
> >  
> > @@ -1343,6 +1346,10 @@ generic_file_aio_read(struct kiocb *iocb, const struct iovec *iov,
> >  		if (desc.count > 0)
> >  			break;
> >  	}
> > +	if (invalidate && retval > 0)
> > +		invalidate_mapping_pages(filp->f_mapping,
> > +					 pos >> PAGE_CACHE_SHIFT,
> > +					 (*ppos - 1) >> PAGE_CACHE_SHIFT);
> 
> A little comment here would be surely useful.  Telling that we want to
> get rid of the pages again if we were falling through from an attempted
> direct I/O read.
> 

Will do.  I'll send an updated patch when you answer my above question.  Thanks
for the review.

Josef
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