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.
Best Regards,
Petr
> + in_preempt_schedule_irq(addr))
> + return -EINVAL;
> +
> + if (ops->address(data, addr, 1))
> + return -EINVAL;
> +
> + print_ftrace_graph_addr(addr, data, ops, tinfo, graph);
> +
> + last_frame = frame;
> + frame = frame->next_frame;
> + ret_addr = &frame->return_address;
> + }
> +
> + if (last_frame + 1 != (void *)task_pt_regs(tinfo->task))
> + return -EINVAL;
> +
> + *bp = (unsigned long)frame;
> + return 0;
> +}
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