Re: [PATCH] tracing/x86/xen: Remove zero data size trace events trace_xen_mmu_flush_tlb{_all}

From: Juergen Gross <jgross@suse.com>
To: Steven Rostedt <rostedt@goodmis.org>,
	LKML <linux-kernel@vger.kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Ingo Molnar <mingo@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Jingjie Jiang <jingjie.jiang@oracle.com>,
	Mukesh Rathor <mukesh.rathor@oracle.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	stable@vger.kernel.org
Subject: Re: [PATCH] tracing/x86/xen: Remove zero data size trace events trace_xen_mmu_flush_tlb{_all}
Date: Fri, 11 May 2018 06:14:07 +0200	[thread overview]
Message-ID: <54c0a807-87e3-866f-aaa8-de383d567d50@suse.com> (raw)
In-Reply-To: <20180509144605.5a220327@gandalf.local.home>

On 09/05/18 20:46, Steven Rostedt wrote:
> 
> From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>
> 
> Doing an audit of trace events, I discovered two trace events in the xen
> subsystem that use a hack to create zero data size trace events. This is not
> what trace events are for. Trace events add memory footprint overhead, and
> if all you need to do is see if a function is hit or not, simply make that
> function noinline and use function tracer filtering.
> 
> Worse yet, the hack used was:
> 
>  __array(char, x, 0)
> 
> Which creates a static string of zero in length. There's assumptions about
> such constructs in ftrace that this is a dynamic string that is nul
> terminated. This is not the case with these tracepoints and can cause
> problems in various parts of ftrace.
> 
> Nuke the trace events!
> 
> Cc: stable@vger.kernel.org
> Fixes: 95a7d76897c1e ("xen/mmu: Use Xen specific TLB flush instead of the generic one.")
> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

Any reason not sending this patch to the Xen maintainers?

I can take it through the Xen tree. :-)

Reviewed-by: Juergen Gross <jgross@suse.com>

Juergen