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

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Message-ID: <CANiq72==rFxaw7+ZQv41Zbr+-fJvHiQVzVucrRFpUzrQtN750w@mail.gmail.com>
Date:   Sat, 24 Feb 2018 00:57:40 +0100
From:   Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To:     Asutosh Das <asutoshd@...eaurora.org>
Cc:     subhashj@...eaurora.org, cang@...eaurora.org,
        vivek.gautam@...eaurora.org, rnayak@...eaurora.org,
        vinholikatti@...il.com, jejb@...ux.vnet.ibm.com,
        martin.petersen@...cle.com, linux-scsi@...r.kernel.org,
        Vijay Viswanath <vviswana@...eaurora.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 9/9] scsi: ufs: Add clock ungating to a separate workqueue

On Wed, Feb 21, 2018 at 5:56 AM, Asutosh Das <asutoshd@...eaurora.org> wrote:
> From: Vijay Viswanath <vviswana@...eaurora.org>
>
> 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@...eaurora.org>
> Signed-off-by: Can Guo <cang@...eaurora.org>
> Signed-off-by: Asutosh Das <asutoshd@...eaurora.org>
> ---
>  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.
>