linux-kernel - Re: [PATCH v3] scsi: sd: fix sd shutdown to issue START STOP UNIT command appropriately

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Message-ID: <9f8d9590-eb2c-4985-82e2-73744980313a@kernel.org>
Date: Tue, 29 Jul 2025 08:15:30 +0900
From: Damien Le Moal <dlemoal@...nel.org>
To: Bart Van Assche <bvanassche@....org>,
 Salomon Dushimirimana <salomondush@...gle.com>
Cc: James.Bottomley@...senpartnership.com, ipylypiv@...gle.com,
 linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
 martin.petersen@...cle.com, vishakhavc@...gle.com
Subject: Re: [PATCH v3] scsi: sd: fix sd shutdown to issue START STOP UNIT
 command appropriately

On 7/29/25 00:47, Bart Van Assche wrote:
> On 7/24/25 2:45 PM, Salomon Dushimirimana wrote:
>> Commit aa3998dbeb3a ("ata: libata-scsi: Disable scsi device
>> manage_system_start_stop") enabled libata EH to manage device power mode
>> trasitions for system suspend/resume and removed the flag from
>> ata_scsi_dev_config. However, since the sd_shutdown() function still
>> relies on the manage_system_start_stop flag, a spin-down command is not
>> issued to the disk with command "echo 1 > /sys/block/sdb/device/delete"
>>
>> sd_shutdown() can be called for both system/runtime start stop
>> operations, so utilize the manage_run_time_start_stop flag set in the
>> ata_scsi_dev_config and issue a spin-down command during disk removal
>> when the system is running. This is in addition to when the system is
>> powering off and manage_shutdown flag is set. The
>> manage_system_start_stop flag will still be used for drivers that still
>> set the flag.
>>
>> Fixes: aa3998dbeb3a ("ata: libata-scsi: Disable scsi device manage_system_start_stop")
>> Signed-off-by: Salomon Dushimirimana <salomondush@...gle.com>
>> ---
>> Changes in v3:
>> - Removed unnecessary tag
>>
>>   drivers/scsi/sd.c | 4 +++-
>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
>> index eeaa6af294b81..282000c761f8e 100644
>> --- a/drivers/scsi/sd.c
>> +++ b/drivers/scsi/sd.c
>> @@ -4173,7 +4173,9 @@ static void sd_shutdown(struct device *dev)
>>   	if ((system_state != SYSTEM_RESTART &&
>>   	     sdkp->device->manage_system_start_stop) ||
>>   	    (system_state == SYSTEM_POWER_OFF &&
>> -	     sdkp->device->manage_shutdown)) {
>> +	     sdkp->device->manage_shutdown) ||
>> +	    (system_state == SYSTEM_RUNNING &&
>> +	     sdkp->device->manage_runtime_start_stop)) {
>>   		sd_printk(KERN_NOTICE, sdkp, "Stopping disk\n");
>>   		sd_start_stop_device(sdkp, 0);
>>   	}
> 
> Runtime power management is not related at all to deleting a LUN through
> sysfs. This patch makes it impossible to understand the sd_shutdown()
> implementation without studying the ATA subsystem and its history.
> Additionally, this patch makes the documentation of
> .manage_runtime_start_stop incorrect.
> 
> There are only two drivers that set .manage_runtime_start_stop: libata
> and the unmaintained sbp2 driver. Has it been considered to test
> sdkp->device->is_ata instead of sdkp->device->manage_runtime_start_stop?

I would rather prefer to not spread the use of device->is_ata further than it
already is. We are not even supposed to be needing that one in the first place,
but SAT is not a perfect specification.

But nevertheless, feel free to send cleanup patches to make this code prettier :)


-- 
Damien Le Moal
Western Digital Research