[PATCH] xfs: ensure we capture IO errors correctly

[Hans-Peter Jansen]

Hi, 

this sounds like stable material after a little simmering..

Cheers,
Pete

Am Freitag, 8. März 2013, 13:01:14 schrieb Dave Chinner:
> From: Dave Chinner <dchinner at redhat.com>
> 
> Failed buffer readahead can leave the buffer in the cache marked
> with an error. Most callers that then issue a subsequent read on the
> buffer do not zero the b_error field out, and so we may incorectly
> detect an error during IO completion due to the stale error value
> left on the buffer.
> 
> Avoid this problem by zeroing the error before IO submission. This
> ensures that the only IO errors that are detected those captured
> from are those captured from bio submission or completion.
> 
> Signed-off-by: Dave Chinner <dchinner at redhat.com>
> ---
>  fs/xfs/xfs_buf.c |    6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
> index 50eb603..82b70bd 100644
> --- a/fs/xfs/xfs_buf.c
> +++ b/fs/xfs/xfs_buf.c
> @@ -1336,6 +1336,12 @@ _xfs_buf_ioapply(
>  	int		size;
>  	int		i;
> 
> +	/*
> +	 * Make sure we capture only current IO errors rather than stale errors
> +	 * left over from previous use of the buffer (e.g. failed readahead).
> +	 */
> +	bp->b_error = 0;
> +
>  	if (bp->b_flags & XBF_WRITE) {
>  		if (bp->b_flags & XBF_SYNCIO)
>  			rw = WRITE_SYNC;