linux-kernel - Re: [PATCH v1 2/3] scsi: ufs: Optimize host lock on transfer requests send/compl paths

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Date:   Tue, 29 Jun 2021 13:41:53 +0800
From:   Can Guo <cang@...eaurora.org>
To:     Bart Van Assche <bvanassche@....org>
Cc:     asutoshd@...eaurora.org, nguyenb@...eaurora.org,
        hongwus@...eaurora.org, linux-scsi@...r.kernel.org,
        kernel-team@...roid.com, Stanley Chu <stanley.chu@...iatek.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>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Bean Huo <beanhuo@...ron.com>,
        Jaegeuk Kim <jaegeuk@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Kiwoong Kim <kwmad.kim@...sung.com>,
        Satya Tangirala <satyat@...gle.com>,
        open list <linux-kernel@...r.kernel.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>
Subject: Re: [PATCH v1 2/3] scsi: ufs: Optimize host lock on transfer requests
 send/compl paths

On 2021-06-29 06:58, Bart Van Assche wrote:
> On 5/24/21 1:36 AM, Can Guo wrote:
>> Current UFS IRQ handler is completely wrapped by host lock, and 
>> because
>> ufshcd_send_command() is also protected by host lock, when IRQ handler
>> fires, not only the CPU running the IRQ handler cannot send new 
>> requests,
>> the rest CPUs can neither. Move the host lock wrapping the IRQ handler 
>> into
>> specific branches, i.e., ufshcd_uic_cmd_compl(), 
>> ufshcd_check_errors(),
>> ufshcd_tmc_handler() and ufshcd_transfer_req_compl(). Meanwhile, to 
>> further
>> reduce occpuation of host lock in ufshcd_transfer_req_compl(), host 
>> lock is
>> no longer required to call __ufshcd_transfer_req_compl(). As per test, 
>> the
>> optimization can bring considerable gain to random read/write 
>> performance.
> 
> Hi Can,
> 
> Since this patch has been applied on the AOSP kernel we see 100%
> reproducible lockups appearing on multiple test setups. Examples of 
> call
> traces:
> 
> blk_execute_rq()
> __scsi_execute()
> sd_sync_cache()
> sd_suspend_common()
> sd_suspend_system()
> scsi_bus_suspend()
> __device_suspend()
> 
> blk_execute_rq()
> __scsi_execute()
> ufshcd_clear_ua_wlun()
> ufshcd_err_handling_unprepare()
> ufshcd_err_handler()
> process_one_work()
> 
> Reverting this patch and the next patch from this series solved the
> lockups. Do you prefer to revert this patch or do you perhaps want us 
> to
> test a potential fix?
> 

Hi Bart,

I am waiting for more infos/logs/dumps on Buganizor to look into it.
With above calltrace snippet, it is hard to figure out what is 
happening.
Besides, we've tested this series before go upstream and we didn't
see such problem.

Thanks,

Can Guo.

> Thanks,
> 
> Bart.