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

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Date:   Tue, 26 Jan 2021 10:10:31 +0800
From:   Can Guo <cang@...eaurora.org>
To:     Avri Altman <Avri.Altman@....com>
Cc:     Bart Van Assche <bvanassche@....org>, jaegeuk@...nel.org,
        asutoshd@...eaurora.org, nguyenb@...eaurora.org,
        hongwus@...eaurora.org, linux-scsi@...r.kernel.org,
        kernel-team@...roid.com, Alim Akhtar <alim.akhtar@...sung.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Stanley Chu <stanley.chu@...iatek.com>,
        Bean Huo <beanhuo@...ron.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] scsi: ufs: Fix some problems in task management
 request implementation

On 2021-01-25 19:36, Avri Altman 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.
>> 
>> Cc: Jaegeuk Kim <jaegeuk@...nel.org>
> Since you are practically reverting Bart's change (69a6c269c097),
> maybe cc him as well,
> And add a fixes tag?
> 

Hi Avri,

It is not reverting Bart's change, but making TMR work properly based
on it. I am ok with the Bart's idea of getting a tag for TMR from
blk_get_request(), and this patch respects that idea.

> Also, even though all those fixes are around the same place, but
> fixing different issues,
> You might want to consider to separate those.  Whatever you think.
> 

Thanks for the suggestion. I treat it as a whole because it is 
convenient
for me to get it ported and tested over different platforms. I may
revise it in next version after more comments come on it.

Thanks,
Can Guo.

> Thanks,
> Avri