lkml.org 
[lkml]   [2014]   [Feb]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] x86: Use preempt_disable_notrace() in cycles_2_ns()
On Tue, 4 Feb 2014, Steven Rostedt wrote:

> When debug preempt is enabled, preempt_disable() can be traced by
> function and function graph tracing.
>
> There's a place in the function graph tracer that calls trace_clock()
> which eventually calls cycles_2_ns() outside of the recursion
> protection. When cycles_2_ns() calls preempt_disable() it gets traced
> and the graph tracer will go into a recursive loop causing a crash or
> worse, a triple fault.
>
> Simple fix is to use preempt_disable_notrace() in cycles_2_ns, which
> makes sense because the preempt_disable() tracing may use that code
> too, and it tracing it, even with recursion protection is rather
> pointless.
>
> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

Acked-by-me

> diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
> index 19e5adb..acb3b60 100644
> --- a/arch/x86/kernel/tsc.c
> +++ b/arch/x86/kernel/tsc.c
> @@ -209,7 +209,7 @@ static inline unsigned long long cycles_2_ns(unsigned long long cyc)
> * dance when its actually needed.
> */
>
> - preempt_disable();
> + preempt_disable_notrace();
> data = this_cpu_read(cyc2ns.head);
> tail = this_cpu_read(cyc2ns.tail);
>
> @@ -229,7 +229,7 @@ static inline unsigned long long cycles_2_ns(unsigned long long cyc)
> if (!--data->__count)
> this_cpu_write(cyc2ns.tail, data);
> }
> - preempt_enable();
> + preempt_enable_notrace();
>
> return ns;
> }
>


\
 
 \ /
  Last update: 2014-02-04 22:01    [W:0.061 / U:0.292 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site