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Re: [PATCH v4 07/22] regulator: core: Reduce critical area in _regulator_get

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On Mon, Sep 07, 2015 at 02:23:32PM +0200, Tomeu Vizoso wrote:
> By moving the locking of regulator_list_mutex into regulator_dev_lookup,
> where it is iterated over. The reference count of the regulator's device
> is increased in case it's unregistered while in use.
> 
> In _regulator_get() the regulator_list_mutex mutex was held for most of
> the function, but that is only strictly needed to protect the list
> lookups.
> 
> This change would be useful if for example regulator devices could be
> registered on demand when a driver requests them. regulator_register()
> could end up being called from within _regulator_get while the lock on
> regulator_list_mutex is being held, causing a deadlock.

The fix for this is to convert the code to use the list maintained by
the driver core for regulator class to iterate the regulators rather
than fiddle about with the locking.  I'm pretty sure the current locking
has problems and I'm worried that this may make those problems worse.

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[PATCH v4 0/22] On-demand device probing Tomeu Vizoso <tomeu.vizoso@collabora.com> - 2015-09-07 14:30 +0200
  [PATCH v4 13/22] backlight: Probe backlight devices on demand Tomeu Vizoso <tomeu.vizoso@collabora.com> - 2015-09-07 14:30 +0200
  [PATCH v4 05/22] gpio: Probe GPIO drivers on demand Tomeu Vizoso <tomeu.vizoso@collabora.com> - 2015-09-07 14:30 +0200
  [PATCH v4 03/22] of/platform: Point to struct device from device node Tomeu Vizoso <tomeu.vizoso@collabora.com> - 2015-09-07 14:30 +0200
  [PATCH v4 09/22] drm: Probe panels on demand Tomeu Vizoso <tomeu.vizoso@collabora.com> - 2015-09-07 14:30 +0200
  [PATCH v4 20/22] driver core: Allow deferring probes until late init Tomeu Vizoso <tomeu.vizoso@collabora.com> - 2015-09-07 14:30 +0200
    Re: [PATCH v4 20/22] driver core: Allow deferring probes until late  init Mark Brown <broonie@kernel.org> - 2015-09-11 14:20 +0200
      Re: [PATCH v4 20/22] driver core: Allow deferring probes until late init Tomeu Vizoso <tomeu.vizoso@collabora.com> - 2015-09-14 11:10 +0200
  [PATCH v4 14/22] usb: phy: Probe phy devices on demand Tomeu Vizoso <tomeu.vizoso@collabora.com> - 2015-09-07 14:30 +0200
  [PATCH v4 15/22] clk: Probe clk providers on demand Tomeu Vizoso <tomeu.vizoso@collabora.com> - 2015-09-07 14:30 +0200
  [PATCH v4 22/22] of/platform: Defer probes of registered devices Tomeu Vizoso <tomeu.vizoso@collabora.com> - 2015-09-07 14:30 +0200
  [PATCH v4 16/22] pinctrl: Probe pinctrl devices on demand Tomeu Vizoso <tomeu.vizoso@collabora.com> - 2015-09-07 14:30 +0200
  [PATCH v4 21/22] driver core: Start processing deferred probes earlier Tomeu Vizoso <tomeu.vizoso@collabora.com> - 2015-09-07 14:30 +0200
    Re: [PATCH v4 21/22] driver core: Start processing deferred probes  earlier Mark Brown <broonie@kernel.org> - 2015-09-11 14:30 +0200
      Re: [PATCH v4 21/22] driver core: Start processing deferred probes earlier Tomeu Vizoso <tomeu.vizoso@collabora.com> - 2015-09-15 15:20 +0200
  [PATCH v4 07/22] regulator: core: Reduce critical area in _regulator_get Tomeu Vizoso <tomeu.vizoso@collabora.com> - 2015-09-07 14:40 +0200
    Re: [PATCH v4 07/22] regulator: core: Reduce critical area in  _regulator_get Mark Brown <broonie@kernel.org> - 2015-09-11 14:20 +0200
  [PATCH v4 11/22] i2c: core: Probe i2c adapters and devices on demand Tomeu Vizoso <tomeu.vizoso@collabora.com> - 2015-09-07 14:40 +0200
  [PATCH v4 12/22] pwm: Probe PWM chip devices on demand Tomeu Vizoso <tomeu.vizoso@collabora.com> - 2015-09-07 14:40 +0200
  [PATCH v4 02/22] ARM: amba: Move reading of periphid to pre_probe() Tomeu Vizoso <tomeu.vizoso@collabora.com> - 2015-09-07 14:40 +0200
  [PATCH v4 01/22] driver core: Add pre_probe callback to bus_type Tomeu Vizoso <tomeu.vizoso@collabora.com> - 2015-09-07 14:40 +0200
    Re: [PATCH v4 01/22] driver core: Add pre_probe callback to bus_type Mark Brown <broonie@kernel.org> - 2015-09-11 14:10 +0200
  [PATCH v4 10/22] drm/tegra: Probe dpaux devices on demand Tomeu Vizoso <tomeu.vizoso@collabora.com> - 2015-09-07 14:40 +0200
  Re: [PATCH v4 0/22] On-demand device probing Rob Herring <robherring2@gmail.com> - 2015-09-07 23:00 +0200
    Re: [PATCH v4 0/22] On-demand device probing Tomeu Vizoso <tomeu.vizoso@collabora.com> - 2015-09-08 09:40 +0200
      Re: [PATCH v4 0/22] On-demand device probing Rob Herring <robh@kernel.org> - 2015-09-09 07:50 +0200
        Re: [PATCH v4 0/22] On-demand device probing Tomeu Vizoso <tomeu.vizoso@collabora.com> - 2015-09-09 11:50 +0200

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