Re: [PATCH 21/22] xfs: %pF is only for function pointers

[Dave Chinner <david@fromorbit.com>]

On Wed, Mar 11, 2015 at 10:13:56PM -0500, Scott Wood wrote:
> Use %pS for actual addresses, otherwise you'll get bad output
> on arches like ppc64 where %pF expects a function descriptor.
> 
> Signed-off-by: Scott Wood <scottwood@freescale.com>
> Cc: xfs@oss.sgi.com

Scott, I've just found that this change (commit 65dd297 "xfs: %pF is
only for function pointers") breaks the symbolic printing in XFS
trace events on x86_64. eg.

> diff --git a/fs/xfs/xfs_trace.h b/fs/xfs/xfs_trace.h
> index 51372e3..b5ac81e 100644
> --- a/fs/xfs/xfs_trace.h
> +++ b/fs/xfs/xfs_trace.h
> @@ -115,7 +115,7 @@ DECLARE_EVENT_CLASS(xfs_perag_class,
>  		__entry->refcount = refcount;
>  		__entry->caller_ip = caller_ip;
>  	),
> -	TP_printk("dev %d:%d agno %u refcount %d caller %pf",
> +	TP_printk("dev %d:%d agno %u refcount %d caller %ps",
>  		  MAJOR(__entry->dev), MINOR(__entry->dev),
>  		  __entry->agno,
>  		  __entry->refcount,

This results in output like this:

760.828474: xfs_perag_get:  dev 253:32 agno 13 refcount 10 caller 0xffffffff814eef02s
760.828476: xfs_perag_put:  dev 253:32 agno 13 refcount 9 caller 0xffffffff814eefe8s

When I revert this commit, I get:

71.911265: xfs_perag_get:   dev 253:32 agno 0 refcount 11 caller xfs_extent_busy_insert
71.911266: xfs_perag_put:   dev 253:32 agno 0 refcount 10 caller xfs_extent_busy_insert

Which is exactly what we should be getting from the tracing. I'm
using trace-cmd to gather and print the events, and it breaks
both old and current versions of trace-cmd.

Can you please look into why this change broke the tracing output
on x86-64 - if there is no obvious/easy fix for it, then I'm simply
going to revert it because having the tracing work correctly on
x86-64 is far more important to us than ppc64 or ia64....

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com