Re: [PATCH v2 4/4] scsi: ufs: Fix up and simplify error recovery mechanism

[Can Guo]

Hi Bart,

On 2020-07-14 11:52, Bart Van Assche wrote:
> On 2020-07-13 19:28, Can Guo wrote:
> > o Queue eh_work on a single threaded workqueue to avoid concurrency 
> > between
> >   eh_works.
>
> Please use another approach (mutex?) to serialize error handling. There 
> are
> already way too workqueues in a running Linux system.
>
> > o According to the UFSHCI JEDEC spec, hibern8 enter/exit error occurs 
> > when
> >   the link is broken. This actaully applies to any power mode change
> >   operations. In this change, if a power mode change operation 
> > (including
> >   AH8 enter/exit) fails, mark the link state as UIC_LINK_BROKEN_STATE 
> > and
> >   schedule eh_work. eh_work needs to do full reset and restore to 
> > recover
> >   the link back to active. Before the link state is recovered to 
> > active by
> >   eh_work, any power mode change attempts just return -ENOLINK to 
> > avoid
> >   consecutive HW error.
> >
> > o To avoid concurrency between eh_work and link recovery, remove link
> >   recovery from hibern8 enter/exit func. If hibern8 enter/exit func 
> > fails,
> >   simply return error code and let eh_work run in parallel.
> >
> > o Recover UFS hba runtime PM error in eh_work. If 
> > ufschd_suspend/resume
> >   fails due to UFS error, e.g. hibern8 enter/exit error and SSU cmd 
> > error,
> >   the runtime PM framework saves the error to dev.power.runtime_error.
> >   After that, hba runtime suspend/resume would not be invoked anymore 
> > until
> >   dev.power.runtime_error is cleared. The runtime PM error can be 
> > recovered
> >   in eh_work by calling pm_runtime_set_active() after reset and 
> > restore
> >   succeeds. Meanwhile, if pm_runtime_set_active() returns no error, 
> > which
> >   means dev.power.runtime_error is cleared, we also need to explicitly
> >   resume those scsi devices under hba in case any of them has failed 
> > to be
> >   resumed due to hba runtime resume error.
> >
> > o Fix a racing problem between eh_work and ufshcd_suspend/resume. In 
> > the
> >   old code, it blocks scsi requests before schedules eh_work, but when
> >   eh_work calls pm_runtime_get_sync(), if ufshcd_suspend/resume is 
> > sending
> >   a scsi cmd, most likely the SSU cmd, pm_runtime_get_sync() will 
> > never
> >   return because scsi requests were blocked. To fix this racing 
> > problem,
> >   o Don't block scsi requests before schedule eh_work, but let eh_work
> >     block scsi requests when eh_work is ready to start error recovery.
> >   o Meanwhile, if eh_work is schueduled due to fatal error, don't 
> > requeue
> >     the scsi cmds sent from ufshcd_suspend/resume path, but simply let 
> > the
> >     scsi cmds fail. If the scsi cmds fail, hba runtime suspend/resume 
> > fails
> >     too, but it does hurt since eh_work recovers hba runtime PM error.
> >
> > o Move host/regs dump in ufshcd_check_errors() to eh_work because 
> > heavy
> >   dump in IRQ context can lead to stability issues. In addition, some 
> > clean
> >   up in ufshcd_print_host_regs() and ufshcd_print_host_state().
>
> The above list is a long list. To me that is a sign that this patch 
> needs to
> be split into multiple patches.
>
> Thanks,
>
> Bart.

Sure, will split it into a few patches.

Thanks,

Can Guo.