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From:   "Rafael J. Wysocki" <rafael@kernel.org>
Date:   Thu, 13 Dec 2018 19:09:15 +0100
Message-ID: <CAJZ5v0hOiL1oWGCmFv2N8-0UvCibXz02DhdFMyUQsQZ1hDjV=w@mail.gmail.com>
Subject: Re: [PATCH] drivers/base: use a worker for sysfs unbind
To:     Daniel Vetter <daniel.vetter@ffwll.ch>
Cc:     "Rafael J. Wysocki" <rafael@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        ramalingam.c@intel.com,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Daniel Vetter <daniel.vetter@intel.com>
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On Thu, Dec 13, 2018 at 5:25 PM Daniel Vetter <daniel.vetter@ffwll.ch> wrote:
>
> On Thu, Dec 13, 2018 at 5:18 PM Rafael J. Wysocki <rafael@kernel.org> wrote:
> >
> > On Thu, Dec 13, 2018 at 1:36 PM Daniel Vetter <daniel.vetter@ffwll.ch> wrote:

[cut]

> > > I can do the old code exactly, but afaict the non-NULL parent just
> > > takes care of the parent bus locking for us, instead of hand-rolling
> > > it in the caller. But if I missed something, I can easily undo that
> > > part.
> >
> > It is different if device links are present, but I'm not worried about
> > that case honestly. :-)
>
> What would change with device links? We have some cleanup plans to
> remove our usage for early/late s/r hooks with a device link, to make
> sure i915 resumes before snd_hda_intel. Digging more into the code I
> only see the temporary dropping of the parent's device_lock, but I
> have no idea what that even implies ...

That's just it (which is why I said I was not worried).

Running device_links_unbind_consumers() with the parent lock held may
deadlock if another child of the same parent also is a consumer of the
current device (which really is a corner case), but the current code
has this problem - it goes away with your change.

But dev->bus->need_parent_lock checks are missing in there AFAICS, let
me cut a patch to fix that.

Cheers,
Rafael