linux-kernel - Re: [PATCH] oprofile, x86: Fix nmi-unsafe callgraph support in, 2.6.27 and later

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Date:	Mon, 13 Jun 2011 09:40:42 -0400
From:	John Lumby <johnlumby@...mail.com>
To:	Robert Richter <robert.richter@....com>
CC:	Maynard Johnson <maynardj@...ibm.com>,
	oprofile list <oprofile-list@...ts.sourceforge.net>,
	<mingo@...e.hu>, <peterz@...radead.org>,
	linux-kernel list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] oprofile, x86: Fix nmi-unsafe callgraph support in,
 2.6.27  and later


On 06/09/11 08:57, Robert Richter wrote:
> On 08.06.11 13:43:56, John Lumby wrote:
>
> "EIP is at print_context_stack=0x45/0xb0
>
> and from a machine-code listing, I found that that offset corresponds
> to the line
>
>         addr = *stack;
>
> in arch/x86/kernel/dumpstack.c"
>
> Actually this should not happen, because of checking the stack pointer
> in valid_stack_ptr(). So could you apply the change below and test if
> this throws a bug message?

I applied that change and,  yes,  it throws the BUG :
     kernel BUG at arch/x86/kernel/dumpstack.c : 76!
It appears that the existing test in valid_stack_ptr makes too many assumptions 
about the other variables involved to catch all cases.

Also,   changing that test by adding a simplistic check for an absolute 
range is not sufficient,  as another crash then occurs in dump_trace at 
the line
        stack = (unsigned long *)context->previous_esp;

This patch to dumpstack_32.c seems to work for my system:
 (although it is probably more of a cover-up than a fix)

--- linux-2.6.39-FLG/arch/x86/kernel/dumpstack_32.c.orig    2011-05-19 
00:06:34.000000000 -0400
+++ linux-2.6.39-FLG/arch/x86/kernel/dumpstack_32.c    2011-06-12 
23:09:16.000000000 -0400
@@ -42,6 +42,19 @@ void dump_trace(struct task_struct *task

          context = (struct thread_info *)
              ((unsigned long)stack & (~(THREAD_SIZE - 1)));
+
+        /* crude bugcheck */
+        if (    ((unsigned long)stack <= 1024)
+             || ((unsigned long)stack >= 0xffffe000)
+             || ((unsigned long)context <= 1024)
+             || ((unsigned long)context >= 0xffffe000)
+                   ) {
+#ifdef NOISY_DUMP_TRACE
+             printk("dump_trace: pid %d stack= %p context= %p\n"
+                   ,(task ? task->pid : -1),stack,context);
+#endif  /* NOISY_DUMP_TRACE  */
+            break;
+                }
          bp = ops->walk_stack(context, stack, bp, ops, data, NULL, &graph);

          stack = (unsigned long *)context->previous_esp;


> Thanks,
>
> -Robert
>
>
> diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
> index e2a3f06..37693f5 100644
> --- a/arch/x86/kernel/dumpstack.c
> +++ b/arch/x86/kernel/dumpstack.c
> @@ -73,6 +73,8 @@ static inline int valid_stack_ptr(struct thread_info *tinfo,
>                          void *p, unsigned int size, void *end)
>   {
>          void *t = tinfo;
> +
> +       BUG_ON(p<  (void *)THREAD_SIZE);
>          if (end) {
>                  if (p<  end&&  p>= (end-THREAD_SIZE))
>                          return 1;
>
 		 	   		  --
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