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

Bart Van Assche
2020-07-14T03:52:28Z

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.