[PATCH] xfs: only trace buffer items if they exist

[Brian Foster]

On Fri, Feb 06, 2015 at 03:46:48PM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner at redhat.com>
> 
> The commit 2d3d0c5 ("xfs: lobotomise xfs_trans_read_buf_map()") left
> a landmine in the tracing code: trace_xfs_trans_buf_read() is now
> call on all buffers that are read through this interface rather than
> just buffers in transactions. For buffers outside transaction
> context, bp->b_fspriv is null, and so the buf log item tracing
> functions cannot be called. This causes a NULL pointer dereference
> in the trace_xfs_trans_buf_read() function when tracing is turned
> on.
> 
> Signed-off-by: Dave Chinner <dchinner at redhat.com>
> ---

Ah, I hit this a week or so ago and completely forgot to dig into it.
Thanks!

Reviewed-by: Brian Foster <bfoster at redhat.com>

>  fs/xfs/xfs_trans_buf.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/xfs/xfs_trans_buf.c b/fs/xfs/xfs_trans_buf.c
> index 0a4d4ab..7579841 100644
> --- a/fs/xfs/xfs_trans_buf.c
> +++ b/fs/xfs/xfs_trans_buf.c
> @@ -327,9 +327,10 @@ xfs_trans_read_buf_map(
>  		return -EIO;
>  	}
>  
> -	if (tp)
> +	if (tp) {
>  		_xfs_trans_bjoin(tp, bp, 1);
> -	trace_xfs_trans_read_buf(bp->b_fspriv);
> +		trace_xfs_trans_read_buf(bp->b_fspriv);
> +	}
>  	*bpp = bp;
>  	return 0;
>  
> -- 
> 2.0.0
> 
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