linux-kernel - Re: [PATCH v1] scsi: ufs: remove clk_scaling

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Message-ID: <366a3afc-071f-ae77-d06d-25ad750976dc@intel.com>
Date:   Mon, 14 Feb 2022 16:31:28 +0200
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Kiwoong Kim <kwmad.kim@...sung.com>,
        'Avri Altman' <Avri.Altman@....com>,
        linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
        alim.akhtar@...sung.com, jejb@...ux.ibm.com,
        martin.petersen@...cle.com, beanhuo@...ron.com,
        cang@...eaurora.org, sc.suh@...sung.com, hy50.seo@...sung.com,
        sh425.lee@...sung.com, bhoon95.kim@...sung.com,
        vkumar.1997@...sung.com
Subject: Re: [PATCH v1] scsi: ufs: remove clk_scaling_lock when clkscaling
 isn't supported.

On 12/02/2022 06:44, Kiwoong Kim wrote:
>> The error handler really should have exclusive access.  One of the places
>> you change does explain that:
>>
>>  		 * Hold the scaling lock just in case dev cmds
>>  		 * are sent via bsg and/or sysfs.
>>  		 */
>> -		down_write(&hba->clk_scaling_lock);
>> +		if (ufshcd_is_clkscaling_supported(hba))
>> +			down_write(&hba->clk_scaling_lock); 
> 
> 
> Yeah.., I saw the comment but didn't get why.
> 
> Is there anyone who knows why it's necessary for all SoCs?
> At lease, I know there is no reason to forbid concurrent executions of dev cmd and power mode change.
> 
> If there's nothing, how about adding a quick to ignore it?

Is it worth it?

The error handler really should have exclusive access.
Have you considered, for example, races of ufshcd_reset_and restore() and dev commands, tm commands, UIC commands.
I suspect more locking is needed not less.