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Date:   Wed, 28 Oct 2020 12:43:52 -0700
From:   Jaegeuk Kim <jaegeuk@kernel.org>
To:     Can Guo <cang@codeaurora.org>
Cc:     linux-kernel@vger.kernel.org, linux-scsi@vger.kernel.org,
        kernel-team@android.com, alim.akhtar@samsung.com,
        avri.altman@wdc.com, bvanassche@acm.org
Subject: Re: [PATCH v4 1/5] scsi: ufs: atomic update for clkgating_enable
Message-ID: <20201028194352.GA3060274@google.com>
References: <20201026195124.363096-1-jaegeuk@kernel.org>
 <20201026195124.363096-2-jaegeuk@kernel.org>
 <20d1c2ca06e95beb207fd4ba1b61dc80@codeaurora.org>
 <20201027033311.GA1745317@google.com>
 <76df977d164683c7404d2dc702f2e5ad@codeaurora.org>
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In-Reply-To: <76df977d164683c7404d2dc702f2e5ad@codeaurora.org>
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On 10/27, Can Guo wrote:
> On 2020-10-27 11:33, Jaegeuk Kim wrote:
> > On 10/27, Can Guo wrote:
> > > On 2020-10-27 03:51, Jaegeuk Kim wrote:
> > > > From: Jaegeuk Kim <jaegeuk@google.com>
> > > >
> > > > When giving a stress test which enables/disables clkgating, we hit
> > > > device
> > > > timeout sometimes. This patch avoids subtle racy condition to address
> > > > it.
> > > >
> > > > Note that, this requires a patch to address the device stuck by
> > > > REQ_CLKS_OFF in
> > > > __ufshcd_release().
> > > >
> > > > The fix is "scsi: ufs: avoid to call REQ_CLKS_OFF to CLKS_OFF".
> > > 
> > > Why don't you just squash the fix into this one?
> > 
> > I'm seeing this patch just revealed that problem.
> 
> That scenario (back to back calling of ufshcd_release()) only happens
> when you stress the clkgate_enable sysfs node, so let's keep the fix
> as one to make things simple. What do you think?

If we don't have this patch, do you think this issue won't happen at all?

> 
> Thanks,
> 
> Can Guo.
> 
> > 
> > > 
> > > Thanks,
> > > 
> > > Can Guo.
> > > 
> > > >
> > > > Signed-off-by: Jaegeuk Kim <jaegeuk@google.com>
> > > > ---
> > > >  drivers/scsi/ufs/ufshcd.c | 12 ++++++------
> > > >  1 file changed, 6 insertions(+), 6 deletions(-)
> > > >
> > > > diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
> > > > index cc8d5f0c3fdc..6c9269bffcbd 100644
> > > > --- a/drivers/scsi/ufs/ufshcd.c
> > > > +++ b/drivers/scsi/ufs/ufshcd.c
> > > > @@ -1808,19 +1808,19 @@ static ssize_t
> > > > ufshcd_clkgate_enable_store(struct device *dev,
> > > >  		return -EINVAL;
> > > >
> > > >  	value = !!value;
> > > > +
> > > > +	spin_lock_irqsave(hba->host->host_lock, flags);
> > > >  	if (value == hba->clk_gating.is_enabled)
> > > >  		goto out;
> > > >
> > > > -	if (value) {
> > > > -		ufshcd_release(hba);
> > > > -	} else {
> > > > -		spin_lock_irqsave(hba->host->host_lock, flags);
> > > > +	if (value)
> > > > +		__ufshcd_release(hba);
> > > > +	else
> > > >  		hba->clk_gating.active_reqs++;
> > > > -		spin_unlock_irqrestore(hba->host->host_lock, flags);
> > > > -	}
> > > >
> > > >  	hba->clk_gating.is_enabled = value;
> > > >  out:
> > > > +	spin_unlock_irqrestore(hba->host->host_lock, flags);
> > > >  	return count;
> > > >  }