Re: [PATCH V2 2/2] fs/super.c: don't fool lockdep in freeze_super() and thaw_super() paths

From: Oleg Nesterov
Date: Thu Oct 13 2016 - 12:59:42 EST

Dave, I am sorry for delay.

On 10/10, Dave Chinner wrote:
> So, it's time to waste more time explaining why lockdep is telling
> us about something that *isn't a bug*.
> [... snip ...]

OK, thanks. I am not surprised although I have to admit I wasn't sure.

> Basically, what we are seeing here is yet another case of "lockdep
> is just smart enough to be really dumb" because we cannot fully
> express or cleanly annotate the contexts in which it is being asked
> to validate.

Yes... perhaps we can add the new lockdep helpers to avoid the false-
positives like this one, but so far it is not clear to me what we can do.
Somehow we need to tell it to to avoid check_prev_add() because we know
that the work function won't take sb_internal, but at the same time we
should complain if it actually does this. Lets ignore this patch for now.