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

[Can Guo]

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@xxxxxxxxxx>
> 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