Re: [PATCH v2] scsi: ufs: Fix some problems in task management request implementation

[Bart Van Assche <bvanassche@acm.org>]

On 1/20/21 7:23 PM, Can Guo wrote:
> Current task management request send/compl implementation is broken, the
> problems and fixes are listed as below:
> 
> Problem: TMR completion timeout. ufshcd_tmc_handler() calls
>          blk_mq_tagset_busy_iter(fn == ufshcd_compl_tm()), but since
>          blk_mq_tagset_busy_iter() only iterates over all reserved tags and
>          started requests, so ufshcd_compl_tm() never gets a chance to run.
> Fix:     Call blk_mq_start_request() in __ufshcd_issue_tm_cmd().
> 
> Problem: Race condition in send/compl paths. ufshcd_compl_tm() looks for
>          all 0 bits in the REG_UTP_TASK_REQ_DOOR_BELL and call complete()
>          for each req who has the req->end_io_data set. There can be a race
>          condition btw tmc send/compl, because req->end_io_data is set, in
>          __ufshcd_issue_tm_cmd(), without host lock protection, so it is
>          possible that when ufshcd_compl_tm() checks the req->end_io_data,
>          req->end_io_data is set but the corresponding tag has not been set
>          in the REG_UTP_TASK_REQ_DOOR_BELL. Thus, ufshcd_tmc_handler() may
>          wrongly complete TMRs which have not been sent.
> Fix:     Protect req->end_io_data with host lock. And let ufshcd_compl_tm()
>          only handle those tm cmds which have been completed instead of
>          looking for 0 bits in the REG_UTP_TASK_REQ_DOOR_BELL.
> 
> Problem: In __ufshcd_issue_tm_cmd(), it is not right to use hba->nutrs +
>          req->tag as the Task Tag in one TMR UPIU.
> Fix:     Directly use req->tag as Task Tag.

Please split this patch into three separate patches - one patch per
problem that has been described above.

Thanks,

Bart.