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SubjectRe: [PATCH 1/1] PM / Domains: Avoid a potential deadlock
Date
On Wednesday, March 13, 2019 8:35:02 AM CET Ulf Hansson wrote:
> On Tue, 12 Mar 2019 at 07:51, Jiada Wang <jiada_wang@mentor.com> wrote:
> >
> > 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
>
> Thanks for the detailed description, this seems like a reasonable change to me!
>
> >
> > Signed-off-by: Jiada Wang <jiada_wang@mentor.com>
>
> Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>

Patch applied, thanks!

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