linux-kernel - Re: [PATCH v7 5/8] scsi: ufs: Fix ufshcd_hold() caused scheduling while atomic

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Message-ID: <2c485ce3fac4d92ab3776daecc1af493@codeaurora.org>
Date:   Mon, 10 Feb 2020 09:28:38 +0800
From:   Can Guo <cang@...eaurora.org>
To:     Avri Altman <Avri.Altman@....com>
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>,
        "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>,
        Stanley Chu <stanley.chu@...iatek.com>,
        Bart Van Assche <bvanassche@....org>,
        Venkat Gopalakrishnan <venkatg@...eaurora.org>,
        Tomas Winkler <tomas.winkler@...el.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 v7 5/8] scsi: ufs: Fix ufshcd_hold() caused scheduling
 while atomic

On 2020-02-06 18:28, Avri Altman wrote:
> Hi,
> 
>> 
>> The async version of ufshcd_hold(async == true), which is only called
>> in queuecommand path as for now, is expected to work in atomic 
>> context,
>> thus it should not sleep or schedule out. When it runs into the 
>> condition
>> that clocks are ON but link is still in hibern8 state, it should bail 
>> out
>> without flushing the clock ungate work.
> 
> Fixes: f2a785ac2312 (scsi: ufshcd: Fix race between clk scaling and 
> ungate work)

Sorry, missed this one, if another version is needed, I will add this 
line.

>> 
>> Signed-off-by: Can Guo <cang@...eaurora.org>
>> Reviewed-by: Hongwu Su <hongwus@...eaurora.org>
>> Reviewed-by: Asutosh Das <asutoshd@...eaurora.org>
>> Reviewed-by: Bean Huo <beanhuo@...ron.com>
>> Reviewed-by: Stanley Chu <stanley.chu@...iatek.com>
>> ---
>>  drivers/scsi/ufs/ufshcd.c | 5 +++++
>>  1 file changed, 5 insertions(+)
>> 
>> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
>> index bbc2607..e8f7f9d 100644
>> --- a/drivers/scsi/ufs/ufshcd.c
>> +++ b/drivers/scsi/ufs/ufshcd.c
>> @@ -1518,6 +1518,11 @@ int ufshcd_hold(struct ufs_hba *hba, bool 
>> async)
>>                  */
>>                 if (ufshcd_can_hibern8_during_gating(hba) &&
>>                     ufshcd_is_link_hibern8(hba)) {
>> +                       if (async) {
>> +                               rc = -EAGAIN;
>> +                               hba->clk_gating.active_reqs--;
>> +                               break;
>> +                       }
>>                         spin_unlock_irqrestore(hba->host->host_lock, 
>> flags);
>>                         flush_work(&hba->clk_gating.ungate_work);
>>                         spin_lock_irqsave(hba->host->host_lock, 
>> flags);
> Since now the above code is shared in all cases,
> Maybe find a more economical way to pack it?
> 
> Thanks,
> Avri
> 
> 

There are only 2 of this same code pieces in ufshcd_hold() and located
in different cases, meanwhile there can be fall through, I don't see
a good way to pack it, can you suggest if you have any ideas?

Regards,
Can Guo.

>> --
>> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora
>> Forum,
>> a Linux Foundation Collaborative Project