lkml.org 
[lkml]   [2009]   [Jun]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 2/3] function-graph: enable the stack after initialization of other variables
On Tue, Jun 02, 2009 at 02:30:38PM -0400, Steven Rostedt wrote:
> From: Steven Rostedt <srostedt@redhat.com>
>
> The function graph tracer checks if the task_struct has ret_stack defined
> to know if it is OK or not to use it. The initialization is done for
> all tasks by one process, but the idle tasks use the same initialization
> used by new tasks.
>
> If an interrupt happens on an idle task that just had the ret_stack
> created, but before the rest of the initialization took place, then
> we can corrupt the return address of the functions.
>
> This patch moves the setting of the task_struct's ret_stack to after
> the other variables have been initialized.
>
> [ Impact: prevent kernel panic on idle task when starting function graph ]
>
> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
> ---
> kernel/trace/ftrace.c | 9 +++++++--
> kernel/trace/trace_functions_graph.c | 6 ++++++
> 2 files changed, 13 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index ebff62e..20e0660 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -2739,15 +2739,20 @@ void unregister_ftrace_graph(void)
> void ftrace_graph_init_task(struct task_struct *t)
> {
> if (atomic_read(&ftrace_graph_active)) {
> - t->ret_stack = kmalloc(FTRACE_RETFUNC_DEPTH
> + struct ftrace_ret_stack *ret_stack;
> +
> + ret_stack = kmalloc(FTRACE_RETFUNC_DEPTH
> * sizeof(struct ftrace_ret_stack),
> GFP_KERNEL);
> - if (!t->ret_stack)
> + if (!ret_stack)
> return;
> t->curr_ret_stack = -1;
> atomic_set(&t->tracing_graph_pause, 0);
> atomic_set(&t->trace_overrun, 0);
> t->ftrace_timestamp = 0;
> + /* make curr_ret_stack visable before we add the ret_stack */
> + smp_wmb();
> + t->ret_stack = ret_stack;
> } else
> t->ret_stack = NULL;
> }


Thanks for fixing this.


> diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
> index d28687e..baeb5fe 100644
> --- a/kernel/trace/trace_functions_graph.c
> +++ b/kernel/trace/trace_functions_graph.c
> @@ -65,6 +65,12 @@ ftrace_push_return_trace(unsigned long ret, unsigned long func, int *depth)
> if (!current->ret_stack)
> return -EBUSY;
>
> + /*
> + * We must make sure the ret_stack is tested before we read
> + * anything else.
> + */
> + smp_rmb();


Isn't this part a too much costly for very traced function?


> +
> /* The return trace stack is full */
> if (current->curr_ret_stack == FTRACE_RETFUNC_DEPTH - 1) {
> atomic_inc(&current->trace_overrun);
> --
> 1.6.3.1
>
> --



\
 
 \ /
  Last update: 2009-06-02 21:05    [W:0.059 / U:22.564 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site