Re: [PATCH] driver core: Ensure proper suspend/resume ordering

From	"Rafael J. Wysocki" <rjw@rjwysocki.net>
Newsgroups	linux.kernel
Subject	Re: [PATCH] driver core: Ensure proper suspend/resume ordering
Date	2015-09-22 02:00 +0200
Message-ID	<qbja2-57d-13@gated-at.bofh.it> (permalink)
References	<qbaq5-Zi-1@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Monday, September 21, 2015 10:34:54 AM Alan Stern wrote:
> On Mon, 21 Sep 2015, Thierry Reding wrote:
> 
> > > > Force-removing drivers that depend on a device that's being unbound
> > > > would be a possibility to solve the problem where consumers depend on a
> > > > device that could physically go away. It might also be the right thing
> > > > to do in any case. Presumably somebody unloading a module want to do
> > > > just that, and refusing to do so isn't playing very nice. Of course
> > > > allowing random modules to be removed even if a lot of consumers might
> > > > depend on it may not be friendly either. Consider if you unload a GPIO
> > > > driver that provides a pin that's used to enable power to an eMMC that
> > > > might have the root filesystem.
> > > >
> > > > Then again, if you unload a module you better know what you're doing
> > > > anyway, so maybe that's not something we need to be concerned about.
> > > 
> > > I think that it's better to fail module unloads in such cases by
> > > default (to prevent simple silly mistakes from having possibly severe
> > > consequences), but if a "force" option is used, we should regard that
> > > as "the user really means it" and do as requested.  That would be very
> > > much analogous to the hot-unplug situation from the software
> > > perspective.
> > 
> > Sounds very reasonable to me.
> 
> I'm not so sure about this.  For one thing, how are you going to 
> distinguish which module unloads are safe?

Ones that have no dependencies?

Very simple: If the driver being unloaded is explicitly depended on by
something (ie. there is a "device link" to it), we fail the unload with
-EBUSY unless the "force" option is used.

> For another, even if you do make this distinction, don't you think 
> people will get into the habit of always using the "force" option?  My 
> impression is that most module unloads end up causing some device to be 
> unbound from a driver, or even completely deregistered.
> 
> Right now the kernel uses the "You better know what you're doing when
> you unload a module" point of view, and I don't see any good reasons
> for changing.

Well, is that point of view appropriate from the users' perspective?

Thanks,
Rafael

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Thread

[PATCH] driver core: Ensure proper suspend/resume ordering Thierry Reding <thierry.reding@gmail.com> - 2015-09-10 12:20 +0200
  Re: [PATCH] driver core: Ensure proper suspend/resume ordering Grygorii Strashko <grygorii.strashko@ti.com> - 2015-09-10 13:00 +0200
  Re: [PATCH] driver core: Ensure proper suspend/resume ordering "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2015-09-10 23:50 +0200
    Re: [PATCH] driver core: Ensure proper suspend/resume ordering Thierry Reding <thierry.reding@gmail.com> - 2015-09-11 14:10 +0200
      Re: [PATCH] driver core: Ensure proper suspend/resume ordering Alan Stern <stern@rowland.harvard.edu> - 2015-09-11 21:10 +0200
        Re: [PATCH] driver core: Ensure proper suspend/resume ordering "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2015-09-12 00:10 +0200
          Re: [PATCH] driver core: Ensure proper suspend/resume ordering Alan Stern <stern@rowland.harvard.edu> - 2015-09-12 19:50 +0200
            Re: [PATCH] driver core: Ensure proper suspend/resume ordering "Rafael J. Wysocki" <rafael@kernel.org> - 2015-09-15 02:50 +0200
              Re: [PATCH] driver core: Ensure proper suspend/resume ordering Alan Stern <stern@rowland.harvard.edu> - 2015-09-15 16:30 +0200
                Re: [PATCH] driver core: Ensure proper suspend/resume ordering "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2015-09-16 02:40 +0200
          Re: [PATCH] driver core: Ensure proper suspend/resume ordering Grygorii Strashko <grygorii.strashko@ti.com> - 2015-09-16 15:50 +0200
            Re: [PATCH] driver core: Ensure proper suspend/resume ordering Alan Stern <stern@rowland.harvard.edu> - 2015-09-16 21:30 +0200
              Re: [PATCH] driver core: Ensure proper suspend/resume ordering "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2015-09-17 01:40 +0200
                Re: [PATCH] driver core: Ensure proper suspend/resume ordering Grygorii Strashko <grygorii.strashko@ti.com> - 2015-09-17 17:50 +0200
                Re: [PATCH] driver core: Ensure proper suspend/resume ordering "Rafael J. Wysocki" <rafael@kernel.org> - 2015-09-18 02:00 +0200
                Re: [PATCH] driver core: Ensure proper suspend/resume ordering "Rafael J. Wysocki" <rafael@kernel.org> - 2015-09-18 02:10 +0200
                Re: [PATCH] driver core: Ensure proper suspend/resume ordering Grygorii Strashko <grygorii.strashko@ti.com> - 2015-10-01 20:20 +0200
        Re: [PATCH] driver core: Ensure proper suspend/resume ordering Thierry Reding <thierry.reding@gmail.com> - 2015-09-15 18:20 +0200
          Re: [PATCH] driver core: Ensure proper suspend/resume ordering Alan Stern <stern@rowland.harvard.edu> - 2015-09-15 21:20 +0200
            Re: [PATCH] driver core: Ensure proper suspend/resume ordering "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2015-09-16 03:10 +0200
              Re: [PATCH] driver core: Ensure proper suspend/resume ordering Grygorii Strashko <grygorii.strashko@ti.com> - 2015-09-16 15:40 +0200
                Re: [PATCH] driver core: Ensure proper suspend/resume ordering Alan Stern <stern@rowland.harvard.edu> - 2015-09-16 19:00 +0200
              Re: [PATCH] driver core: Ensure proper suspend/resume ordering Alan Stern <stern@rowland.harvard.edu> - 2015-09-16 19:10 +0200
            Re: [PATCH] driver core: Ensure proper suspend/resume ordering Thierry Reding <thierry.reding@gmail.com> - 2015-09-16 15:20 +0200
              Re: [PATCH] driver core: Ensure proper suspend/resume ordering Alan Stern <stern@rowland.harvard.edu> - 2015-09-16 21:30 +0200
                Re: [PATCH] driver core: Ensure proper suspend/resume ordering "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2015-09-17 02:00 +0200
                Re: [PATCH] driver core: Ensure proper suspend/resume ordering "Rafael J. Wysocki" <rafael@kernel.org> - 2015-09-17 04:10 +0200
                Re: [PATCH] driver core: Ensure proper suspend/resume ordering Alan Stern <stern@rowland.harvard.edu> - 2015-09-17 19:10 +0200
                Re: [PATCH] driver core: Ensure proper suspend/resume ordering "Rafael J. Wysocki" <rafael@kernel.org> - 2015-09-17 20:50 +0200
                Re: [PATCH] driver core: Ensure proper suspend/resume ordering Alan Stern <stern@rowland.harvard.edu> - 2015-09-17 23:10 +0200
                Re: [PATCH] driver core: Ensure proper suspend/resume ordering "Rafael J. Wysocki" <rafael@kernel.org> - 2015-09-18 02:20 +0200
                Re: [PATCH] driver core: Ensure proper suspend/resume ordering Thierry Reding <thierry.reding@gmail.com> - 2015-09-18 18:00 +0200
                Re: [PATCH] driver core: Ensure proper suspend/resume ordering "Rafael J. Wysocki" <rafael@kernel.org> - 2015-09-19 01:10 +0200
                Re: [PATCH] driver core: Ensure proper suspend/resume ordering Thierry Reding <thierry.reding@gmail.com> - 2015-09-21 11:00 +0200
                Re: [PATCH] driver core: Ensure proper suspend/resume ordering Alan Stern <stern@rowland.harvard.edu> - 2015-09-21 16:40 +0200
                Re: [PATCH] driver core: Ensure proper suspend/resume ordering "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2015-09-22 02:00 +0200
                Re: [PATCH] driver core: Ensure proper suspend/resume ordering Alan Stern <stern@rowland.harvard.edu> - 2015-09-22 03:30 +0200
                Re: [PATCH] driver core: Ensure proper suspend/resume ordering "Rafael J. Wysocki" <rafael@kernel.org> - 2015-09-22 02:40 +0200
                Re: [PATCH] driver core: Ensure proper suspend/resume ordering Tomeu Vizoso <tomeu.vizoso@collabora.com> - 2015-09-17 07:50 +0200
                Re: [PATCH] driver core: Ensure proper suspend/resume ordering "Rafael J. Wysocki" <rafael@kernel.org> - 2015-09-17 20:20 +0200
                Re: [PATCH] driver core: Ensure proper suspend/resume ordering Alan Stern <stern@rowland.harvard.edu> - 2015-09-17 21:30 +0200
      Re: [PATCH] driver core: Ensure proper suspend/resume ordering "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2015-09-12 00:20 +0200
        Re: [PATCH] driver core: Ensure proper suspend/resume ordering Thierry Reding <thierry.reding@gmail.com> - 2015-09-15 18:00 +0200
          Re: [PATCH] driver core: Ensure proper suspend/resume ordering "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2015-09-16 03:00 +0200
            Re: [PATCH] driver core: Ensure proper suspend/resume ordering Grygorii Strashko <grygorii.strashko@ti.com> - 2015-09-16 15:40 +0200
              Re: [PATCH] driver core: Ensure proper suspend/resume ordering "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2015-09-17 02:30 +0200
    Re: [PATCH] driver core: Ensure proper suspend/resume ordering Alan Stern <stern@rowland.harvard.edu> - 2015-09-11 16:10 +0200

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