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Commit 2071ac98 authored by Jiada Wang's avatar Jiada Wang Committed by Rafael J. Wysocki
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PM / Domains: Avoid a potential deadlock 



Lockdep warns that prepare_lock and genpd->mlock can cause a deadlock
the deadlock scenario is like following:
First thread is probing cs2000
cs2000_probe()
  clk_register()
    __clk_core_init()
      clk_prepare_lock()                            ----> acquires prepare_lock
        cs2000_recalc_rate()
          i2c_smbus_read_byte_data()
            rcar_i2c_master_xfer()
              dma_request_chan()
                rcar_dmac_of_xlate()
                  rcar_dmac_alloc_chan_resources()
                    pm_runtime_get_sync()
                      __pm_runtime_resume()
                        rpm_resume()
                          rpm_callback()
                            genpd_runtime_resume()   ----> acquires genpd->mlock

Second thread is attaching any device to the same PM domain
genpd_add_device()
  genpd_lock()                                       ----> acquires genpd->mlock
    cpg_mssr_attach_dev()
      of_clk_get_from_provider()
        __of_clk_get_from_provider()
          __clk_create_clk()
            clk_prepare_lock()                       ----> acquires prepare_lock

Since currently no PM provider access genpd's critical section
in .attach_dev, and .detach_dev callbacks, so there is no need to protect
these two callbacks with genpd->mlock.
This patch avoids a potential deadlock by moving out .attach_dev and .detach_dev
from genpd->mlock, so that genpd->mlock won't be held when prepare_lock is acquired
in .attach_dev and .detach_dev

Signed-off-by: default avatarJiada Wang <jiada_wang@mentor.com>
Reviewed-by: default avatarUlf Hansson <ulf.hansson@linaro.org>
Tested-by: default avatarGeert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: default avatarGeert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
parent 9e98c678

drivers/base/power/domain.c

+6 −7
Original line number Diff line number Diff line
@@ -1469,12 +1469,12 @@ static int genpd_add_device(struct generic_pm_domain *genpd, struct device *dev, 
	if (IS_ERR(gpd_data))

		return PTR_ERR(gpd_data);



	genpd_lock(genpd);



	ret = genpd->attach_dev ? genpd->attach_dev(genpd, dev) : 0;

	if (ret)

		goto out;



	genpd_lock(genpd);



	dev_pm_domain_set(dev, &genpd->domain);



	genpd->device_count++;
@@ -1482,9 +1482,8 @@ static int genpd_add_device(struct generic_pm_domain *genpd, struct device *dev, 


	list_add_tail(&gpd_data->base.list_node, &genpd->dev_list);



 out:

	genpd_unlock(genpd);



 out:

	if (ret)

		genpd_free_dev_data(dev, gpd_data);

	else
@@ -1533,15 +1532,15 @@ static int genpd_remove_device(struct generic_pm_domain *genpd, 
	genpd->device_count--;

	genpd->max_off_time_changed = true;



	if (genpd->detach_dev)

		genpd->detach_dev(genpd, dev);



	dev_pm_domain_set(dev, NULL);



	list_del_init(&pdd->list_node);



	genpd_unlock(genpd);



	if (genpd->detach_dev)

		genpd->detach_dev(genpd, dev);



	genpd_free_dev_data(dev, gpd_data);



	return 0;