Re: [PATCH 1/4 V2] xfs: catch buffers written without verifiers attached

[Brian Foster <bfoster@redhat.com>]

On Wed, Jul 30, 2014 at 12:30:24PM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
> 
> We recently had a bug where buffers were slipping through log
> recovery without any verifier attached to them. This was resulting
> in on-disk CRC mismatches for valid data. Add some warning code to
> catch this occurrence so that we catch such bugs during development
> rather than not being aware they exist.
> 
> Note that we cannot do this verification unconditionally as non-CRC
> filesystems don't always attach verifiers to the buffers being
> written. e.g. during log recovery we cannot identify all the
> different types of buffers correctly on non-CRC filesystems, so we
> can't attach the correct verifiers in all cases and so we don't
> attach any. Hence we don't want on non-CRC filesystems to avoid
> spamming the logs with false indications.
> 
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---
>  fs/xfs/xfs_buf.c | 15 +++++++++++++++
>  fs/xfs/xfs_log.c |  7 ++++++-
>  2 files changed, 21 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
> index a6dc83e..078b8be 100644
> --- a/fs/xfs/xfs_buf.c
> +++ b/fs/xfs/xfs_buf.c
> @@ -1330,6 +1330,21 @@ _xfs_buf_ioapply(
>  						   SHUTDOWN_CORRUPT_INCORE);
>  				return;
>  			}
> +		} else if (bp->b_bn != -1LL) {
> +			struct xfs_mount *mp = bp->b_target->bt_mount;
> +
> +			/*
> +			 * non-crc filesystems don't attach verifiers during
> +			 * log recovery, so don't warn for such filesystems.
> +			 */
> +			if (xfs_sb_version_hascrc(&mp->m_sb)) {
> +				xfs_warn(mp,
> +					"%s: no ops on block 0x%llx/0x%llx",
> +					__func__, bp->b_bn,
> +					bp->b_maps[0].bm_bn);

Are you intending to print both block number values here or the
b_bn/bm_len combo?

> +				xfs_hex_dump(bp->b_addr, 64);
> +				dump_stack();
> +			}
>  		}
>  	} else if (bp->b_flags & XBF_READ_AHEAD) {
>  		rw = READA;
> diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
> index 149a4a5..9dc92b3 100644
> --- a/fs/xfs/xfs_log.c
> +++ b/fs/xfs/xfs_log.c
> @@ -1378,8 +1378,13 @@ xlog_alloc_log(
>  
>  	xlog_get_iclog_buffer_size(mp, log);
>  
> +	/*
> +	 * Use a block number of -1 for the extra log buffer used during splits
> +	 * so that it will trigger errors if we ever try to do IO on it without
> +	 * first having set it up properly.
> +	 */
>  	error = -ENOMEM;
> -	bp = xfs_buf_alloc(mp->m_logdev_targp, 0, BTOBB(log->l_iclog_size), 0);
> +	bp = xfs_buf_alloc(mp->m_logdev_targp, -1LL, BTOBB(log->l_iclog_size), 0);

How about XFS_BUF_DADDR_NULL (here and above)?

Brian

>  	if (!bp)
>  		goto out_free_log;
>  
> 
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