On Tue, Mar 04, 2014 at 04:03:25PM -0800, tip-bot for Jiri Olsa wrote:
FWIW I also prefer this patch.
> @@ -1252,9 +1249,11 @@ dotraplinkage void __kprobes
> do_page_fault(struct pt_regs *regs, unsigned long error_code)
> {
> enum ctx_state prev_state;
> + /* Get the faulting address: */
> + unsigned long address = read_cr2();
>
> prev_state = exception_enter();
> - __do_page_fault(regs, error_code);
> + __do_page_fault(regs, error_code, address);
> exception_exit(prev_state);
> }
>
> @@ -1271,9 +1270,16 @@ dotraplinkage void __kprobes
> trace_do_page_fault(struct pt_regs *regs, unsigned long error_code)
> {
> enum ctx_state prev_state;
> + /*
> + * The exception_enter and tracepoint processing could
> + * trigger another page faults (user space callchain
> + * reading) and destroy the original cr2 value, so read
> + * the faulting address now.
> + */
> + unsigned long address = read_cr2();
>
> prev_state = exception_enter();
> trace_page_fault_entries(regs, error_code);
> - __do_page_fault(regs, error_code);
> + __do_page_fault(regs, error_code, address);
> exception_exit(prev_state);
> }
How about also marking these two functions as notrace? That would also
avoid getting __mcount calls from before we read CR2.
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