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  wrote:

From: Vijay Viswanath 

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 
Signed-off-by: Can Guo 
Signed-off-by: Asutosh Das 
---
  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(>clk_gating.ungate_work);
+   queue_work(hba->clk_gating.clk_gating_workq,
+  >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(>clk_gating.gate_work, ufshcd_gate_work);
 INIT_WORK(>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, >clk_gating.enable_attr);
 cancel_work_sync(>clk_gating.ungate_work);
 cancel_delayed_work_sync(>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

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

[Miguel Ojeda]

On Wed, Feb 21, 2018 at 5:56 AM, Asutosh Das  wrote:
> From: Vijay Viswanath 
>
> 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 
> Signed-off-by: Can Guo 
> Signed-off-by: Asutosh Das 
> ---
>  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(>clk_gating.ungate_work);
> +   queue_work(hba->clk_gating.clk_gating_workq,
> +  >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(>clk_gating.gate_work, ufshcd_gate_work);
> INIT_WORK(>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, >clk_gating.enable_attr);
> cancel_work_sync(>clk_gating.ungate_work);
> cancel_delayed_work_sync(>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.
>

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

[Asutosh Das]

From: Vijay Viswanath 

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
a rescue thread which will be called when the above deadlock
condition is possible.

Signed-off-by: Vijay Viswanath 
Signed-off-by: Can Guo 
Signed-off-by: Asutosh Das 
---
 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(>clk_gating.ungate_work);
+   queue_work(hba->clk_gating.clk_gating_workq,
+  >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(>clk_gating.gate_work, ufshcd_gate_work);
INIT_WORK(>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);
+
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, >clk_gating.enable_attr);
cancel_work_sync(>clk_gating.ungate_work);
cancel_delayed_work_sync(>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.