Re: [PATCH v3] scsi: core: clear driver private data when retry request

[yebin <yebin@huaweicloud.com>]

On 2025/2/17 17:44, John Garry wrote:
> On 17/02/2025 02:16, Ye Bin wrote:
>> From: Ye Bin <yebin10@huawei.com>
>>
>> After commit 1bad6c4a57ef
>> ("scsi: zero per-cmd private driver data for each MQ I/O"),
>> xen-scsifront/virtio_scsi/snic driver remove code that zeroes
>> driver-private command data. If request do retry will lead to
>> driver-private command data remains. Before commit 464a00c9e0ad
>> ("scsi: core: Kill DRIVER_SENSE") if virtio_scsi do capacity
>> expansion, first request may return UA then request will do retry,
>> as driver-private command data remains, request will return UA
>> again.
>
> So are there any drivers which expect this sort of behavior, i.e. keep
> private data between retries?

No driver that depends on the last state is found. If yes, the driver
should provide the init_cmd_priv function to manage private data. In
this way, the SCSI middle layer ignores the private data of the driver.

>
>> As a result, the request keeps retrying, and the request
>> times out and fails.
>> So zeroes driver-private command data when request do retry.
>>
>> Fixes: f7de50da1479 ("scsi: xen-scsifront: Remove code that zeroes
>> driver-private command data")
>> Fixes: c2bb87318baa ("scsi: virtio_scsi: Remove code that zeroes
>> driver-private command data")
>> Fixes: c3006a926468 ("scsi: snic: Remove code that zeroes
>> driver-private command data")
>> Signed-off-by: Ye Bin <yebin10@huawei.com>
>
>> ---
>
> Ps: in future, please list the changes per version here
>
Thanks for the heads-up.
>>   drivers/scsi/scsi_lib.c | 14 +++++++-------
>>   1 file changed, 7 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
>> index be0890e4e706..f1cfe0bb89b2 100644
>> --- a/drivers/scsi/scsi_lib.c
>> +++ b/drivers/scsi/scsi_lib.c
>> @@ -1669,13 +1669,6 @@ static blk_status_t scsi_prepare_cmd(struct
>> request *req)
>>       if (in_flight)
>>           __set_bit(SCMD_STATE_INFLIGHT, &cmd->state);
>> -    /*
>> -     * Only clear the driver-private command data if the LLD does not
>> supply
>> -     * a function to initialize that data.
>> -     */
>> -    if (!shost->hostt->init_cmd_priv)
>> -        memset(cmd + 1, 0, shost->hostt->cmd_size);
>> -
>>       cmd->prot_op = SCSI_PROT_NORMAL;
>>       if (blk_rq_bytes(req))
>>           cmd->sc_data_direction = rq_dma_dir(req);
>> @@ -1842,6 +1835,13 @@ static blk_status_t scsi_queue_rq(struct
>> blk_mq_hw_ctx *hctx,
>>       if (!scsi_host_queue_ready(q, shost, sdev, cmd))
>>           goto out_dec_target_busy;
>> +    /*
>> +     * Only clear the driver-private command data if the LLD does not
>> supply
>> +     * a function to initialize that data.
>> +     */
>> +    if (shost->hostt->cmd_size && !shost->hostt->init_cmd_priv)
>> +        memset(cmd + 1, 0, shost->hostt->cmd_size);
>> +
>>       if (!(req->rq_flags & RQF_DONTPREP)) {
>>           ret = scsi_prepare_cmd(req);
>>           if (ret != BLK_STS_OK)
>