linux-kernel - Re: [PATCH V2 2/2] fs/super.c: don't fool lockdep in freeze_super() and thaw

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Date:   Thu, 13 Oct 2016 18:58:08 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Dave Chinner <david@...morbit.com>
Cc:     Jan Kara <jack@...e.cz>, Al Viro <viro@...iv.linux.org.uk>,
        Nikolay Borisov <kernel@...p.com>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        fstests@...r.kernel.org
Subject: Re: [PATCH V2 2/2] fs/super.c: don't fool lockdep in
        freeze_super() and thaw_super() paths

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.

Oleg.