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

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Date:   Tue, 14 Jul 2020 12:26:06 +0800
From:   Can Guo <cang@...eaurora.org>
To:     Bart Van Assche <bvanassche@....org>
Cc:     asutoshd@...eaurora.org, nguyenb@...eaurora.org,
        hongwus@...eaurora.org, rnayak@...eaurora.org,
        linux-scsi@...r.kernel.org, kernel-team@...roid.com,
        saravanak@...gle.com, salyzyn@...gle.com,
        Alim Akhtar <alim.akhtar@...sung.com>,
        Avri Altman <avri.altman@....com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Stanley Chu <stanley.chu@...iatek.com>,
        Nitin Rawat <nitirawa@...eaurora.org>,
        Tomas Winkler <tomas.winkler@...el.com>,
        Bean Huo <beanhuo@...ron.com>,
        Satya Tangirala <satyat@...gle.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 4/4] scsi: ufs: Fix up and simplify error recovery
 mechanism

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.