Re: [PATCH 9/9] scsi: ufs: Add clock ungating to a separate workqueue

[Asutosh Das (asd)]

On 2/24/2018 5:27 AM, Miguel Ojeda wrote:
> On Wed, Feb 21, 2018 at 5:56 AM, Asutosh Das <asutoshd@xxxxxxxxxxxxxx> wrote:
> > From: Vijay Viswanath <vviswana@xxxxxxxxxxxxxx>
> >
> > UFS driver can receive a request during memory reclaim by kswapd.
> > So when ufs driver puts the ungate work in queue, and if there are no
> > idle workers, kthreadd is invoked to create a new kworker. Since
> > kswapd task holds a mutex which kthreadd also needs, this can cause
> > a deadlock situation. So ungate work must be done in a separate
> > work queue with WQ__RECLAIM flag enabled.Such a workqueue will have
>
> WQ_MEM_RECLAIM here. Also space after dot.
>
> > a rescue thread which will be called when the above deadlock
> > condition is possible.
> >
> > Signed-off-by: Vijay Viswanath <vviswana@xxxxxxxxxxxxxx>
> > Signed-off-by: Can Guo <cang@xxxxxxxxxxxxxx>
> > Signed-off-by: Asutosh Das <asutoshd@xxxxxxxxxxxxxx>
> > ---
> >   drivers/scsi/ufs/ufshcd.c | 10 +++++++++-
> >   drivers/scsi/ufs/ufshcd.h |  1 +
> >   2 files changed, 10 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
> > index 6541e1d..bb3382a 100644
> > --- a/drivers/scsi/ufs/ufshcd.c
> > +++ b/drivers/scsi/ufs/ufshcd.c
> > @@ -1503,7 +1503,8 @@ int ufshcd_hold(struct ufs_hba *hba, bool async)
> >                  hba->clk_gating.state = REQ_CLKS_ON;
> >                  trace_ufshcd_clk_gating(dev_name(hba->dev),
> >                                          hba->clk_gating.state);
> > -               schedule_work(&hba->clk_gating.ungate_work);
> > +               queue_work(hba->clk_gating.clk_gating_workq,
> > +                          &hba->clk_gating.ungate_work);
> >                  /*
> >                   * fall through to check if we should wait for this
> >                   * work to be done or not.
> > @@ -1689,6 +1690,8 @@ static ssize_t ufshcd_clkgate_enable_store(struct device *dev,
> >
> >   static void ufshcd_init_clk_gating(struct ufs_hba *hba)
> >   {
> > +       char wq_name[sizeof("ufs_clk_gating_00")];
> > +
> >          if (!ufshcd_is_clkgating_allowed(hba))
> >                  return;
> >
> > @@ -1696,6 +1699,10 @@ static void ufshcd_init_clk_gating(struct ufs_hba *hba)
> >          INIT_DELAYED_WORK(&hba->clk_gating.gate_work, ufshcd_gate_work);
> >          INIT_WORK(&hba->clk_gating.ungate_work, ufshcd_ungate_work);
> >
> > +       snprintf(wq_name, ARRAY_SIZE(wq_name), "ufs_clk_gating_%d",
> > +                hba->host->host_no);
> > +       hba->clk_gating.clk_gating_workq = create_singlethread_workqueue(wq_name);
>
> Shouldn't this be alloc_ordered_workqueue() with WQ_MEM_RECLAIM then?
> (create_singlethread_workqueue() and friends are deprecated).
>
> Cheers,
> Miguel
>
> > +
> >          hba->clk_gating.is_enabled = true;
> >
> >          hba->clk_gating.delay_attr.show = ufshcd_clkgate_delay_show;
> > @@ -1723,6 +1730,7 @@ static void ufshcd_exit_clk_gating(struct ufs_hba *hba)
> >          device_remove_file(hba->dev, &hba->clk_gating.enable_attr);
> >          cancel_work_sync(&hba->clk_gating.ungate_work);
> >          cancel_delayed_work_sync(&hba->clk_gating.gate_work);
> > +       destroy_workqueue(hba->clk_gating.clk_gating_workq);
> >   }
> >
> >   /* Must be called with host lock acquired */
> > diff --git a/drivers/scsi/ufs/ufshcd.h b/drivers/scsi/ufs/ufshcd.h
> > index 4385741..570c33e 100644
> > --- a/drivers/scsi/ufs/ufshcd.h
> > +++ b/drivers/scsi/ufs/ufshcd.h
> > @@ -361,6 +361,7 @@ struct ufs_clk_gating {
> >          struct device_attribute enable_attr;
> >          bool is_enabled;
> >          int active_reqs;
> > +       struct workqueue_struct *clk_gating_workq;
> >   };
> >
> >   struct ufs_saved_pwr_info {
> > --
> > Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc.
> > Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project.

Hi Miguel
Thanks for the review.

I'll check this and put up the changes in v2.


-asd

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