[Crash-utility] [PATCH v2 03/10] back_trace: don't check /proc if !LOCAL_ACTIVE()

[Dave Anderson]

----- Original Message -----
> On 04/28, Dave Anderson wrote:
> >
> >
> > > --- a/kernel.c
> > > +++ b/kernel.c
> > > @@ -2902,7 +2902,7 @@ back_trace(struct bt_info *bt)
> > >
> > >  	if (ACTIVE() && !INSTACK(esp, bt)) {
> > >  		sprintf(buf, "/proc/%ld", bt->tc->pid);
> > > -		if (!file_exists(buf, NULL))
> > > +		if (!(LOCAL_ACTIVE() && file_exists(buf, NULL)))
> > >  			error(INFO, "task no longer exists\n");
> > >  		else
> > >  			error(INFO,
> > > --
> > > 2.5.0
> >
> > This doesn't make sense to me.  If it's !LOCAL_ACTIVE() (i.e. hybrid-live-dump), then
> > why would you want to call file_exists()?
> 
> It won't be called in this case, please see below.
> 
> > Shouldn't it be: LOCAL_ACTIVE() and !file_exists()
> 
> This is what I did initially... then decided that error("task no longer exists\n")
> makes more sense if !LOCAL_ACTIVE() && !INSTACK(esp, bt).
> 
> IOW. with the patch above the code actually does
> 
> 	if (ACTIVE() && !INSTACK(...)) {
> 		if (LOCAL_ACTIVE() && file_exists(...))
> 			error("invalid/stale stack pointer");
> 		else
> 			error("task no longer exists\n");
> 	}
> 
> is it wrong?
> 
> I thought that !INSTACK() here likely means the task has gone, but back_trace()
> does the additional file_exists() to verify this, and "invalid/stale stack pointer"
> error means that something was wrong.
> 
> No?
 
I can't even remember -- that code's been in place for so long I'd prefer to just
leave it as-is, and for you to just add something like this: 

        if (ACTIVE() && !INSTACK(esp, bt)) {
+               if (!(LOCAL_ACTIVE()) }
+                       error(INFO, "whatever error message you'd like\n");
+                       return;
+               }
                sprintf(buf, "/proc/%ld", bt->tc->pid);
                if (!file_exists(buf, NULL))
                        error(INFO, "task no longer exists\n");
                else
                        error(INFO,
                            "invalid/stale stack pointer for this task: %lx\n",
                                esp);
                return;
        }

Dave