Re: [PATCH v3 1/5] scsi: ufs: atomic update for clkgating_enable

[Can Guo]

On 2020-10-26 14:13, Jaegeuk Kim wrote:
> On 10/26, Can Guo wrote:
> > On 2020-10-24 23:06, Jaegeuk Kim wrote:
> > > From: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
> > >
> > > When giving a stress test which enables/disables clkgating, we hit
> > > device
> > > timeout sometimes. This patch avoids subtle racy condition to address
> > > it.
> > >
> > > If we use __ufshcd_release(), I've seen that gate_work can be called in
> > > parallel
> > > with ungate_work, which results in UFS timeout when doing hibern8.
> > > Should avoid it.
> > >
> >
> > I don't understand this comment. gate_work and ungate_work are queued 
> > on
> > an ordered workqueue and an ordered workqueue executes at most one 
> > work item
> > at any given time in the queued order. How can the two run in 
> > parallel?
>
> When I hit UFS stuck, I saw this by clkgating tracepoint.
>
> - REQ_CLK_OFF
> - CLKS_OFF
> - REQ_CLK_OFF
> - REQ_CLKS_ON
> ..

I don't see how can you tell that the two works are running in parallel
just from above trace. May I know what is the exact error by "UFS 
timeout
when doing hibern8"?

By using __ufshcd_release() here, I do see one potential issue if your 
test
quickly toggles on/off of clk_gating - disable it, enable it, disable it 
and
enable it, which will cause that __ufshcd_release() being called twice, 
meaning
we queue two gate_works back to back. So can you try below code and let 
me know
if it helps or not? I am OK with your current change, but I would like 
to
understand the problem. Thanks.

diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
index 1791bce..3eee438 100644
--- a/drivers/scsi/ufs/ufshcd.c
+++ b/drivers/scsi/ufs/ufshcd.c
@@ -2271,6 +2271,8 @@ static void ufshcd_gate_work(struct work_struct 
*work)
        unsigned long flags;

        spin_lock_irqsave(hba->host->host_lock, flags);
+       if (hba->clk_gating.state == CLKS_OFF)
+               goto rel_lock;
        /*
         * In case you are here to cancel this work the gating state
         * would be marked as REQ_CLKS_ON. In this case save time by

Regards,

Can Guo.

> By using active_req, I don't see any problem.
>
> > Thanks,
> >
> > Can Guo.
> >
> > > Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
> > > ---
> > >  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 b8f573a02713..e0b479f9eb8a 100644
> > > --- a/drivers/scsi/ufs/ufshcd.c
> > > +++ b/drivers/scsi/ufs/ufshcd.c
> > > @@ -1807,19 +1807,19 @@ 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)
> > > +		hba->clk_gating.active_reqs--;
> > > +	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;
> > >  }