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

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Date:	Mon, 14 Jun 2010 04:17:36 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Josef Bacik <josef@...hat.com>
Cc:	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 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?

>  	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.

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