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

Can Guo
2020-07-14T09:13:20Z

Hi Bart,

On 2020-07-14 12:26, Can Guo wrote:
> 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.
>>

Yeah, mutex works, but in this change, we need to flush the eh_work. As
per
test, in real cases, flush_work can trigger warnings if the work is
queued on
system_wq. Please check func check_flush_dependency().

>>> 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.

I tried, but I find it hard to split it as it works as a whole, it is a
refactor
change rather than a mixture of multiple fixes. I will try to refine the
commit
msg in next version. So it goes just as it is now.

Thanks,

Can Guo.