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

[yebin <yebin@huaweicloud.com>]

On 2025/2/12 1:24, Bart Van Assche wrote:
> On 2/10/25 6:03 AM, 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. 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>
>> ---
>>   drivers/scsi/scsi_lib.c | 19 +++++++++++++------
>>   1 file changed, 13 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
>> index be0890e4e706..5b0c109c89bb 100644
>> --- a/drivers/scsi/scsi_lib.c
>> +++ b/drivers/scsi/scsi_lib.c
>> @@ -1645,6 +1645,17 @@ static unsigned int
>> scsi_mq_inline_sgl_size(struct Scsi_Host *shost)
>>           sizeof(struct scatterlist);
>>   }
>> +static inline void scsi_clear_lld_private_data(struct scsi_cmnd *cmd,
>> +                           struct Scsi_Host *shost)
>> +{
>> +    /*
>> +     * 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 && shost->hostt->cmd_size)
>> +        memset(cmd + 1, 0, shost->hostt->cmd_size);
>> +}
>> +
>>   static blk_status_t scsi_prepare_cmd(struct request *req)
>>   {
>>       struct scsi_cmnd *cmd = blk_mq_rq_to_pdu(req);
>> @@ -1669,12 +1680,7 @@ 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);
>> +    scsi_clear_lld_private_data(cmd, shost);
>>       cmd->prot_op = SCSI_PROT_NORMAL;
>>       if (blk_rq_bytes(req))
>> @@ -1848,6 +1854,7 @@ static blk_status_t scsi_queue_rq(struct
>> blk_mq_hw_ctx *hctx,
>>               goto out_dec_host_busy;
>>           req->rq_flags |= RQF_DONTPREP;
>>       } else {
>> +        scsi_clear_lld_private_data(cmd, shost);
>>           clear_bit(SCMD_STATE_COMPLETE, &cmd->state);
>>       }
>
> Thanks for the detailed analysis. Has the following (untested) simpler
> alternative been considered?
>
Thank you for your reply.
I've considered your modification plan, but I think it's a little hard 
to understand and the code feels a little loose. Of course, it's just my 
own idea.

> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index d776f13cd160..6ee2903b4adb 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -1664,13 +1664,6 @@ 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);
> @@ -1837,6 +1830,13 @@ 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->init_cmd_priv && shost->hostt->cmd_size)
> +        memset(scsi_cmd_priv(cmd), 0, shost->hostt->cmd_size);
> +
>       if (!(req->rq_flags & RQF_DONTPREP)) {
>           ret = scsi_prepare_cmd(req);
>           if (ret != BLK_STS_OK)
>
>