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

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Message-ID: <fe00619c-f337-397f-9ccf-7babda095210@acm.org>
Date:   Mon, 13 Jul 2020 20:52:20 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Can Guo <cang@...eaurora.org>, 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
Cc:     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

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.