linux-kernel - Re: [PATCH v1] scsi: ufs: Fix ufshcd_scale

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Date:   Mon, 1 Aug 2022 10:34:51 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Stanley Chu <chu.stanley@...il.com>
Cc:     Stanley Chu <stanley.chu@...iatek.com>, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        "Martin K . Petersen" <martin.petersen@...cle.com>,
        Avri Altman <avri.altman@....com>, alim.akhtar@...sung.com,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        peter.wang@...iatek.com, Chun-Hung Wu <chun-hung.wu@...iatek.com>,
        alice.chao@...iatek.com, powen.kao@...iatek.com,
        mason.zhang@...iatek.com, qilin.tan@...iatek.com,
        lin.gui@...iatek.com, eddie.huang@...iatek.com,
        tun-yu.yu@...iatek.com, cc.chou@...iatek.com,
        chaotian.jing@...iatek.com, jiajie.hao@...iatek.com
Subject: Re: [PATCH v1] scsi: ufs: Fix ufshcd_scale_clks decision in recovery
 flow

On 7/30/22 00:08, Stanley Chu wrote:
> Hi Bart,
> 
> On Sat, Jul 30, 2022 at 4:12 AM Bart Van Assche <bvanassche@....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?

Thanks,

Bart.