On Wed, Jul 31, 2013 at 05:54:11AM -0400, Tejun Heo wrote:
> Hello,
>
> On Wed, Jul 31, 2013 at 11:44:34AM +0200, Uwe Kleine-König wrote:
> > > > OK, so the possible problem is that remove is called while the irq is
> > > > still active. That means you have to assert that all resources the irq
>
> If your driver destruction path is running while your irq handler is
> still running, it's a crappy / broken driver. You need a deactivation
Well, you cannot avoid assuming that the irq is still active when your
driver's remove callback is called. But I agree about crappyness at the
end of the destruction path. The problem is that crap is as easy as:
probe(..)
{
clk = devm_get_clk(...);
clk_prepare_enable(clk);
writel(1, base + IRQENABLE);
devm_request_irq(...);
}
remove(..)
{
writel(0, base + IRQENABLE);
clk_disable_unprepare(clk);
}
and I think there are more and more drivers doing that.
> step whether you're using devm or not. IRQs can be shared and the
> device should be in a quiesced state before the driver detaches
> itself. Note that you can queue deactivation routine using devm. For
> an example, please take a look at
> drivers/ata/libata-core.c::ata_host_start().
>
> > > > handler is using (e.g. ioremap, clk_prepare_enable) are only freed
> > > > *after* the irq is done. For ioremap that means it must be done using
> > > > devm_ioremap_resource. For a clock it's not that easy because the irq
> > > > handler has to assert that a used clk is kept prepared which can only be
> > > > done using clk_prepare which in turn is not allowed in an irq handler.
> > >
> > > > Hmm. So the only possible fixes are
> > > > - devm* can be told to also care about clk_disable_unprepare
> > > > - after disabling irqs in the remove callback wait for all
> > > > active irqs to be done. (i.e. call synchronize_irq(irq))
> > > > - don't use devm_request_irq
>
> Again, the right thing to do is having a proper deactivation step.
> This is nothing devm can do automatically. There's no way for it to
> find out that the device is actually quiesced. Let's say it waits for
> the current instance of irq handler to finish. How would it know that
> it won't start again between the flushing of the current instance and
> irq deregistration. Add an explicit deactivation step using
> devres_alloc().
>
> > > I'm not sure that devm_ guarantees any ordering in the cleanups it does
> > > so I'd not like to rely on the first option either, if there were some
> > > guarantee of that it'd help. The nice thing about explicitly freeing
> > > the IRQ is that you can tell that all this stuff is safe by inspection.
> > devm_* at least uses list_for_each_entry_reverse
> > (drivers/base/devres.c:release_nodes()). Without this guarantee devm_
> > would not make much sense IMHO.
>
> devm guarantees that the destruction callbacks are called in the
> reverse order of registration.
That's fine.
Best regards
Uwe
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | http://www.pengutronix.de/ |
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