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Subject: RE: Re: [PATCH v4] PM / devfreq: Synchronize
 device_monitor_[start/stop]
Reply-To: myungjoo.ham@samsung.com
Sender: MyungJoo Ham <myungjoo.ham@samsung.com>
From:   MyungJoo Ham <myungjoo.ham@samsung.com>
To:     Mukesh Ojha <quic_mojha@quicinc.com>,
        Chanwoo Choi <cw00.choi@samsung.com>
CC:     Kyungmin Park <kyungmin.park@samsung.com>,
        "linux-pm@vger.kernel.org" <linux-pm@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "huangzaiyang@oppo.com" <huangzaiyang@oppo.com>,
        CPGS <cpgs@samsung.com>
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Date:   Tue, 12 Dec 2023 09:27:02 +0900
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References: <CGME20231206105023epcas1p443ebecc35010d2577b86c3fa23e24e45@epcms1p6>
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On 11/25/2023 2:41 AM, Mukesh Ojha wrote:
> There is a chance if a frequent switch of the governor
> done in a loop result in timer list corruption where
> timer cancel being done from two place one from
> cancel_delayed_work_sync() and followed by expire_timers()
> can be seen from the traces[1].
>
> while true
> do
>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 echo "simple_ondemand" > /sys/class/dev=
freq/1d84000.ufshc/governor
>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 echo "performance" > /sys/class/devfreq=
/1d84000.ufshc/governor
> done
>
> It looks to be issue with devfreq driver where
> device_monitor_[start/stop] need to synchronized so that
> delayed work should get corrupted while it is either
> being queued or running or being cancelled.
>
> Let's use polling flag and devfreq lock to synchronize the
> queueing the timer instance twice and work data being
> corrupted.

Would you please identify the resources to be protected by this lock
and specify them in the devfreq->lock declaration?
(it seems the list of protected resources is growing, and
we need to track them.)

Acked-by: MyungJoo Ham <myungjoo.ham@samsung.com>