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From:   Stanley Chu <chu.stanley@gmail.com>
Date:   Tue, 2 Aug 2022 08:31:12 +0800
Message-ID: <CAGaU9a97KYYJNy2wPWZXX8sjB4NMbX1KB1sVQ95GWHGfn27iEg@mail.gmail.com>
Subject: Re: [PATCH v1] scsi: ufs: Fix ufshcd_scale_clks decision in recovery flow
To:     Bart Van Assche <bvanassche@acm.org>
Cc:     Stanley Chu <stanley.chu@mediatek.com>, linux-scsi@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        "Martin K . Petersen" <martin.petersen@oracle.com>,
        Avri Altman <avri.altman@wdc.com>,
        ALIM AKHTAR <alim.akhtar@samsung.com>,
        "James E.J. Bottomley" <jejb@linux.ibm.com>,
        peter.wang@mediatek.com, Chun-Hung Wu <chun-hung.wu@mediatek.com>,
        alice.chao@mediatek.com, powen.kao@mediatek.com,
        mason.zhang@mediatek.com, qilin.tan@mediatek.com,
        lin.gui@mediatek.com, eddie.huang@mediatek.com,
        tun-yu.yu@mediatek.com, cc.chou@mediatek.com,
        chaotian.jing@mediatek.com, jiajie.hao@mediatek.com
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Hi Bart,

On Tue, Aug 2, 2022 at 1:34 AM Bart Van Assche <bvanassche@acm.org> wrote:
>
> On 7/30/22 00:08, Stanley Chu wrote:
> > Hi Bart,
> >
> > On Sat, Jul 30, 2022 at 4:12 AM Bart Van Assche <bvanassche@acm.org> wrote:
> >>
> >> On 7/29/22 00:55, Stanley Chu wrote:
> >>> diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c
> >>> index 581d88af07ab..dc57a7988023 100644
> >>> --- a/drivers/ufs/core/ufshcd.c
> >>> +++ b/drivers/ufs/core/ufshcd.c
> >>> @@ -1574,8 +1574,6 @@ static ssize_t ufshcd_clkscale_enable_store(struct device *dev,
> >>>        ufshcd_rpm_get_sync(hba);
> >>>        ufshcd_hold(hba, false);
> >>>
> >>> -     hba->clk_scaling.is_enabled = value;
> >>> -
> >>>        if (value) {
> >>>                ufshcd_resume_clkscaling(hba);
> >>>        } else {
> >>> @@ -1586,6 +1584,8 @@ static ssize_t ufshcd_clkscale_enable_store(struct device *dev,
> >>>                                        __func__, err);
> >>>        }
> >>>
> >>> +     hba->clk_scaling.is_enabled = value;
> >>> +
> >>>        ufshcd_release(hba);
> >>>        ufshcd_rpm_put_sync(hba);
> >>>    out:
> >>> @@ -7259,7 +7259,8 @@ static int ufshcd_host_reset_and_restore(struct ufs_hba *hba)
> >>>        hba->silence_err_logs = false;
> >>>
> >>>        /* scale up clocks to max frequency before full reinitialization */
> >>> -     ufshcd_scale_clks(hba, true);
> >>> +     if (ufshcd_is_clkscaling_supported(hba) && hba->clk_scaling.is_enabled)
> >>> +             ufshcd_scale_clks(hba, true);
> >>>
> >>>        err = ufshcd_hba_enable(hba);
> >>
> >> I see a race condition between the hba->clk_scaling.is_enabled check in
> >> ufshcd_host_reset_and_restore() and the code that sets
> >> ufshcd_clkscale_enable_store(). Shouldn't the code in
> >> ufshcd_host_reset_and_restore() that scales up the clocks be serialized
> >> against ufshcd_clkscale_enable_store()?
> >
> > Both check and set paths are serialized by hba->host_sem currently.
> >
> > Would I miss any other unserialized paths?
>
> Where in ufshcd_host_reset_and_restore() or in its callers is
> hba->host_sem obtained? I don't see it. Am I perhaps overlooking something?

It looks like that some callers do not obtain hba->host_sem. I will
fix this in the next version.

The direct callers of ufshcd_host_reset_and_restore() are,

- ufshcd_link_recovery(), host_sem is obtained by its callers:
ufshcd_err_handler() and ufshcd_wl_resume()
- ufshcd_reset_and_restore(): the same as above
- __ufshcd_wl_suspend(): host_sem is obtained by the caller
ufshcd_wl_suspend() but not obtained by other callers.

Thanks,

Stanley