linux-kernel - Re: [PATCH v2 1/2] Revert "drivers: qcom: rpmh-rsc: Use rcuidle tracepoints for rpmh"

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Date:   Tue, 29 Sep 2020 14:23:35 +0530
From:   Maulik Shah <mkshah@...eaurora.org>
To:     John Stultz <john.stultz@...aro.org>
Cc:     Bjorn Andersson <bjorn.andersson@...aro.org>,
        Andy Gross <andy.gross@...aro.org>,
        lkml <linux-kernel@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Doug Anderson <dianders@...omium.org>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Lina Iyer <ilina@...eaurora.org>, lsrao@...eaurora.org,
        Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>
Subject: Re: [PATCH v2 1/2] Revert "drivers: qcom: rpmh-rsc: Use rcuidle
 tracepoints for rpmh"

Hi,

On 9/29/2020 2:17 AM, John Stultz wrote:
> On Tue, Aug 25, 2020 at 4:22 AM Maulik Shah <mkshah@...eaurora.org> wrote:
>> Commit efde2659b0fe ("drivers: qcom: rpmh-rsc: Use rcuidle tracepoints
>> for rpmh") was written to fix a bug seen in an unmerged series that
>> implemented a struct generic_pm_domain::power_off() callback calling
>> rpmh_flush(). See stack trace below.
>>
>>       Call trace:
>>        dump_backtrace+0x0/0x174
>>        show_stack+0x20/0x2c
>>        dump_stack+0xc8/0x124
>>        lockdep_rcu_suspicious+0xe4/0x104
>>        __tcs_buffer_write+0x230/0x2d0
>>        rpmh_rsc_write_ctrl_data+0x210/0x270
>>        rpmh_flush+0x84/0x24c
>>        rpmh_domain_power_off+0x78/0x98
>>        _genpd_power_off+0x40/0xc0
>>        genpd_power_off+0x168/0x208
>>
>> Later the final merged solution is to use CPU PM notification to invoke
>> rpmh_flush() and power_off() callback of genpd is not implemented in the
>> driver.
>>
>> CPU PM notifiers are run with RCU enabled/watching (see cpu_pm_notify()
>> and how it calls rcu_irq_enter_irqson() before calling the notifiers).
>>
>> Remove this change since RCU will not be idle during CPU PM notifications
>> hence not required to use _rcuidle tracepoint. Using _rcuidle tracepoint
>> prevented rpmh driver to be loadable module as these are not exported
>> symbols.
>>
>> This reverts commit efde2659b0fe835732047357b2902cca14f054d9.
>>
>> Cc: Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
>> Cc: John Stultz <john.stultz@...aro.org>
>> Cc: Stephen Rothwell <sfr@...b.auug.org.au>
>> Reviewed-by: Stephen Boyd <swboyd@...omium.org>
>> Reviewed-by: Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
>> Reviewed-by: Ulf Hansson <ulf.hansson@...aro.org>
>> Signed-off-by: Maulik Shah <mkshah@...eaurora.org>
> Hey Maulik!
>    Thanks so much for sending out this series!  I noticed this hasn't
> made it to -next yet, so would it be good to resubmit it?
>
> thanks
> -john

Sure i will resend the series.

Thanks,
Maulik

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