On Fri, Apr 29, 2016 at 11:06:53AM -0700, Andy Lutomirski wrote: > On Thu, Apr 28, 2016 at 1:44 PM, Josh Poimboeuf <jpoimboe@xxxxxxxxxx> wrote: > > A preempted function might not have had a chance to save the frame > > pointer to the stack yet, which can result in its caller getting skipped > > on a stack trace. > > > > Add a flag to indicate when the task has been preempted so that stack > > dump code can determine whether the stack trace is reliable. > > I think I like this, but how do you handle the rather similar case in > which a task goes to sleep because it's waiting on IO that happened in > response to get_user, put_user, copy_from_user, etc? Hm, good question. I was thinking that page faults had a dedicated stack, but now looking at the entry and traps code, that doesn't seem to be the case. Anyway I think it shouldn't be a problem if we make sure that any kernel function which might trigger a valid page fault (e.g., copy_user_generic_string) do the proper frame pointer setup first. Then the stack should still be reliable. In fact I might be able to teach objtool to enforce that: any function which uses an exception table should create a stack frame. Or alternatively, maybe set some kind of flag for page faults, similar to what I did with this patch. -- Josh -- To unsubscribe from this list: send the line "unsubscribe live-patching" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
