On Mon, Apr 04, 2016 at 05:55:01PM +0200, Petr Mladek wrote:
> On Fri 2016-03-25 14:34:54, Josh Poimboeuf wrote:
> > For live patching and possibly other use cases, a stack trace is only
> > useful if you can be assured that it's completely reliable. Add a new
> > save_stack_trace_tsk_reliable() function to achieve that.
> >
> > Scenarios which indicate that a stack strace may be unreliable:
> >
> > - interrupt stacks
> > - preemption
> > - corrupted stack data
> > - newly forked tasks
> > - running tasks
> > - the user didn't provide a large enough entries array
> >
> > Also add a config option so arch-independent code can determine at build
> > time whether the function is implemented.
> >
> > diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
> > index 3b10518..9c68bfc 100644
> > --- a/arch/x86/kernel/dumpstack.c
> > +++ b/arch/x86/kernel/dumpstack.c
> > @@ -145,6 +145,42 @@ int print_context_stack_bp(struct thread_info *tinfo,
> > }
> > EXPORT_SYMBOL_GPL(print_context_stack_bp);
> >
> > +int print_context_stack_reliable(struct thread_info *tinfo,
> > + unsigned long *stack, unsigned long *bp,
> > + const struct stacktrace_ops *ops,
> > + void *data, unsigned long *end, int *graph)
> > +{
> > + struct stack_frame *frame = (struct stack_frame *)*bp;
> > + struct stack_frame *last_frame = frame;
>
> I tried to debug why the patching never finishes as reported by Mirek.
> This initialization breaks the whole function, see below.
> I would initialize last_frame to NULL or maybe (void *)stack.
>
>
> > + unsigned long *ret_addr = &frame->return_address;
> > +
> > + if (test_ti_thread_flag(tinfo, TIF_FORK))
> > + return -EINVAL;
> > +
> > + while (valid_stack_ptr(tinfo, ret_addr, sizeof(*ret_addr), end)) {
> > + unsigned long addr = *ret_addr;
> > +
> > + if (frame <= last_frame || !__kernel_text_address(addr) ||
>
> frame == last_frame in the very rist iteration, so we always return -EINVAL.
Ah, right, thanks for debugging it. I actually did test an earlier
iteration of the function, but obviously didn't test this one.
--
Josh
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