windfarm: decrement client count when unregistering
pebolle at tiscali.nl
Fri Aug 7 08:21:47 AEST 2015
On wo, 2015-08-05 at 14:16 +1000, Michael Ellerman wrote:
> On Fri, 2015-31-07 at 12:08:58 UTC, Paul Bolle wrote:
> > windfarm_corex_exit() contains:
> > BUG_ON(wf_client_count != 0);
> > I wonder why that, apparently. never triggered.
> Hmm interesting.
> A quick test here on an iMacG5 shows that we get into a state where we can't
> remove windfarm_core:
> $ lsmod
> Module Size Used by
> windfarm_smu_sensors 7549 2
> windfarm_core 15391 1 windfarm_smu_sensors
> Which means we can't trigger windfarm_core_exit() and the BUG_ON().
Perhaps this is what, roughly, happens:
/* Let's assume this happens ... */
ads->sens.ops = &smu_cpuamp_ops
ads->sens.name = "cpu-current"
/* ditto ... */
ads->sens.ops = &smu_cpuvolt_ops
ads->sens.name = "cpu-voltage"
/* ... so this would then be true */
if (volt_sensor && curr_sensor)
/* and we do this */
try_module_get(volt_sensor->sens->ops->owner /* THIS_MODULE */)
try_module_get(curr_sensor->sens->ops->owner /* THIS_MODULE */)
The cleanup would have happened here:
/* would this also be done for sensors that never
* triggered a call to module_get()? */
module_put(ads->sens->ops->owner /* THIS MODULE */)
But, whatever it is that smu_sensors_exit() wants to do, it will never
be called since there are these two references to this module that
smu_sensors_init() created itself, preventing the unloading of this
Does the above look plausible?
Note that this was only cobbled together by staring at the code for far
too long. If I had some powerpc machine at hand I could have actually
tested this with a few strategically placed printk()'s.
> I also get an oops when removing windfarm_lm75_sensor, so I suspect there are
> gremlins in the module ref counting for windfarm.
(This I haven't (yet) looked into.)
> I'll merge this as probably correct.
Hope this helps,
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