Re: cred_guard_mutex vs seq_file::lock [was: Re: 3.14.0+/x86: lockdep and mutexes not getting along]

From: Kirill A. Shutemov
Date: Wed Jul 30 2014 - 18:35:19 EST

On Fri, Apr 11, 2014 at 04:07:25PM +0100, Al Viro wrote:
> On Fri, Apr 11, 2014 at 03:50:27PM +0100, David Howells wrote:
> > Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> >
> > > Al, David, any bright ideas on how to best fix this?
> >
> > Have the seq_xxx() code throw an error if current->in_execve is true. I can't
> > think of any circumstance where execve() should be reading anything that uses
> > seq_xxx().
> *cringe*
> I don't like it. That really should be a responsiblity of specific ->show();
> "I'm going to take that mutex, bugger off if we are in execve()" makes a lot
> more sense than having e.g. seq_read() care of that. IOW, I would very
> much prefer the patch you've sent last week.
> And yes, it might leave lockdep false positives, but that's better dealt with
> by annotating the sucker ("this guy has a separate lockdep class for its
> ->lock"). E.g. by splitting proc_single_file_operations in two and having
> the one used for those files do lockdep_set_class() in its ->open().

I've got annoyed by the lockdep warning. What about the patch below?