linux-kernel - Re: [PATCH V2] PM / OPP: Call notifier without holding opp

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Message-id: <59C300AD.6000309@samsung.com>
Date:   Thu, 21 Sep 2017 08:58:37 +0900
From:   Chanwoo Choi <cw00.choi@...sung.com>
To:     Viresh Kumar <viresh.kumar@...aro.org>,
        Rafael Wysocki <rjw@...ysocki.net>,
        Viresh Kumar <vireshk@...nel.org>, Nishanth Menon <nm@...com>,
        Stephen Boyd <sboyd@...eaurora.org>
Cc:     linux-pm@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        myungjoo.ham@...sung.com, inki.dae@...sung.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2] PM / OPP: Call notifier without holding
 opp_table->lock

Hi Viresh,

On 2017년 09월 21일 05:25, Viresh Kumar wrote:
> The notifier callbacks may want to call some OPP helper routines which
> may try to take the same opp_table->lock again and cause a deadlock. One
> such usecase was reported by Chanwoo Choi, where calling
> dev_pm_opp_disable() leads us to the devfreq's OPP notifier handler,
> which further calls dev_pm_opp_find_freq_floor() and it deadlocks.
> 
> We don't really need the opp_table->lock to be held across the notifier
> call though, all we want to make sure is that the 'opp' doesn't get
> freed while being used from within the notifier chain. We can do it with
> help of dev_pm_opp_get/put() as well. Let's do it.
> 
> Reported-by: Chanwoo Choi <cw00.choi@...sung.com>
> Reviewed-by: Stephen Boyd <sboyd@...eaurora.org>
> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> ---
> V1->V2:
> - s/Lets/Let's/ in commit log and added Stephen's tag.
> 

Thanks for your fixup. Looks good to me.
IMHO, this patch should be posted to stable@...r.kernel.org.

Tested-by: Chanwoo Choi <cw00.choi@...sung.com>
Reviewed-by: Chanwoo Choi <cw00.choi@...sung.com>

[snip] 

-- 
Best Regards,
Chanwoo Choi
Samsung Electronics