Re: [PATCH] drivers/base: use a worker for sysfs unbind
From: Rafael J. Wysocki
Date: Mon Dec 17 2018 - 19:03:34 EST
On Mon, Dec 17, 2018 at 8:48 PM Daniel Vetter <daniel@xxxxxxxx> wrote:
> On Thu, Dec 13, 2018 at 07:09:15PM +0100, Rafael J. Wysocki wrote:
> > On Thu, Dec 13, 2018 at 5:25 PM Daniel Vetter <daniel.vetter@xxxxxxxx> wrote:
> > >
> > > On Thu, Dec 13, 2018 at 5:18 PM Rafael J. Wysocki <rafael@xxxxxxxxxx> wrote:
> > > >
> > > > On Thu, Dec 13, 2018 at 1:36 PM Daniel Vetter <daniel.vetter@xxxxxxxx> 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.
> With your patch before this one, are you ok with mine? Or want me to
> respin with a different flavour?
Having reconsidered this a bit I'm leaning towards annotating the
locks - if that works. After all, what is problematic is the lockdep
false-positive and addressing it that way would be most natural IMO.