On Tue, May 04, 2021 at 06:13:39PM -0500, Madhavan T. Venkataraman wrote: > > > On 5/4/21 4:52 PM, Josh Poimboeuf wrote: > > On Mon, May 03, 2021 at 12:36:12PM -0500, madvenka@xxxxxxxxxxxxxxxxxxx wrote: > >> @@ -44,6 +44,8 @@ int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame) > >> unsigned long fp = frame->fp; > >> struct stack_info info; > >> > >> + frame->reliable = true; > >> + > > > > Why set 'reliable' to true on every invocation of unwind_frame()? > > Shouldn't it be remembered across frames? > > > > This is mainly for debug purposes in case a caller wants to print the whole stack and also > print which functions are unreliable. For livepatch, it does not make any difference. It will > quit as soon as it encounters an unreliable frame. Hm, ok. So 'frame->reliable' refers to the current frame, not the entire stack. > > Also, it looks like there are several error scenarios where it returns > > -EINVAL but doesn't set 'reliable' to false. > > > > I wanted to make a distinction between an error situation (like stack corruption where unwinding > has to stop) and an unreliable situation (where unwinding can still proceed). E.g., when a > stack trace is taken for informational purposes or debug purposes, the unwinding will try to > proceed until either the stack trace ends or an error happens. Ok, but I don't understand how that relates to my comment. Why wouldn't a stack corruption like !on_accessible_stack() set 'frame->reliable' to false? In other words: for livepatch purposes, how does the caller tell the difference between hitting the final stack record -- which returns an error with reliable 'true' -- and a stack corruption like !on_accessible_stack(), which also returns an error with reliable 'true'? Surely the latter should be considered unreliable? -- Josh
