[PATCH 0/5] drm/vblank: Cleanup spin_(un)lock_irqsave() calls

[PATCH 0/5] drm/vblank: Cleanup spin_(un)lock_irqsave() calls

[Lyude Paul]

This is a follow-up series for finishing the work that we started here:

https://patchwork.freedesktop.org/patch/373107/?series=74805&rev=8

tl;dr many of the drm_vblank functions only get called within
irq-enabled contexts, so we go through those and convert them over to
using spin_(un)lock_irq() to make this fact more obvious in case we need
to add more blocking calls to any of these functions in the future.

Lyude Paul (5):
  drm/vblank: Use spin_(un)lock_irq() in drm_crtc_vblank_reset()
  drm/vblank: Use spin_(un)lock_irq() in drm_crtc_vblank_on()
  drm/vblank: Use spin_(un)lock_irq() in
    drm_legacy_vblank_post_modeset()
  drm/vblank: Use spin_(un)lock_irq() in drm_queue_vblank_event()
  drm/vblank: Use spin_(un)lock_irq() in drm_crtc_queue_sequence_ioctl()

 drivers/gpu/drm/drm_vblank.c | 29 ++++++++++++-----------------
 1 file changed, 12 insertions(+), 17 deletions(-)

-- 
2.26.2

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[PATCH 1/5] drm/vblank: Use spin_(un)lock_irq() in drm_crtc_vblank_reset()

[Lyude Paul]

All of the drivers in the kernel tree only call this from one of the
following contexts:

* drm_crtc_funcs->reset
* During initial module load

Since both of these contexts are guaranteed to have interrupts enabled
beforehand, there's no need to use the irqsave/irqrestore variants of
spin_(un)lock(). So, fix this to make the irq context of this function
more obvious.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
---
 drivers/gpu/drm/drm_vblank.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
index f402c75b9d343..6af78aecea9d4 100644
--- a/drivers/gpu/drm/drm_vblank.c
+++ b/drivers/gpu/drm/drm_vblank.c
@@ -1363,11 +1363,10 @@ EXPORT_SYMBOL(drm_crtc_vblank_off);
 void drm_crtc_vblank_reset(struct drm_crtc *crtc)
 {
 	struct drm_device *dev = crtc->dev;
-	unsigned long irqflags;
 	unsigned int pipe = drm_crtc_index(crtc);
 	struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
 
-	spin_lock_irqsave(&dev->vbl_lock, irqflags);
+	spin_lock_irq(&dev->vbl_lock);
 	/*
 	 * Prevent subsequent drm_vblank_get() from enabling the vblank
 	 * interrupt by bumping the refcount.
@@ -1376,7 +1375,7 @@ void drm_crtc_vblank_reset(struct drm_crtc *crtc)
 		atomic_inc(&vblank->refcount);
 		vblank->inmodeset = 1;
 	}
-	spin_unlock_irqrestore(&dev->vbl_lock, irqflags);
+	spin_unlock_irq(&dev->vbl_lock);
 
 	drm_WARN_ON(dev, !list_empty(&dev->vblank_event_list));
 	drm_WARN_ON(dev, !list_empty(&vblank->pending_work));
-- 
2.26.2

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[PATCH 2/5] drm/vblank: Use spin_(un)lock_irq() in drm_crtc_vblank_on()

[Lyude Paul]

This is only called from:
* Atomic modesetting hooks
* Module probing routines
* Legacy modesetting hooks

All of which have IRQs enabled, so we can also get rid of
irqsave/restore here to make the IRQ context of this function more
obvious.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
---
 drivers/gpu/drm/drm_vblank.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
index 6af78aecea9d4..9891e82939e35 100644
--- a/drivers/gpu/drm/drm_vblank.c
+++ b/drivers/gpu/drm/drm_vblank.c
@@ -1428,12 +1428,11 @@ void drm_crtc_vblank_on(struct drm_crtc *crtc)
 	struct drm_device *dev = crtc->dev;
 	unsigned int pipe = drm_crtc_index(crtc);
 	struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
-	unsigned long irqflags;
 
 	if (drm_WARN_ON(dev, pipe >= dev->num_crtcs))
 		return;
 
-	spin_lock_irqsave(&dev->vbl_lock, irqflags);
+	spin_lock_irq(&dev->vbl_lock);
 	drm_dbg_vbl(dev, "crtc %d, vblank enabled %d, inmodeset %d\n",
 		    pipe, vblank->enabled, vblank->inmodeset);
 
@@ -1451,7 +1450,7 @@ void drm_crtc_vblank_on(struct drm_crtc *crtc)
 	 */
 	if (atomic_read(&vblank->refcount) != 0 || drm_vblank_offdelay == 0)
 		drm_WARN_ON(dev, drm_vblank_enable(dev, pipe));
-	spin_unlock_irqrestore(&dev->vbl_lock, irqflags);
+	spin_unlock_irq(&dev->vbl_lock);
 }
 EXPORT_SYMBOL(drm_crtc_vblank_on);
 
-- 
2.26.2

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[PATCH 3/5] drm/vblank: Use spin_(un)lock_irq() in drm_legacy_vblank_post_modeset()

[Lyude Paul]

This function is only ever called from ioctl context, so we're
guaranteed to have interrupts enabled. Stop using the irqsave/irqrestore
variants of spin_(un)lock_irq() to make this more obvious.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
---
 drivers/gpu/drm/drm_vblank.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
index 9891e82939e35..51f2e988205e7 100644
--- a/drivers/gpu/drm/drm_vblank.c
+++ b/drivers/gpu/drm/drm_vblank.c
@@ -1551,7 +1551,6 @@ static void drm_legacy_vblank_post_modeset(struct drm_device *dev,
 					   unsigned int pipe)
 {
 	struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
-	unsigned long irqflags;
 
 	/* vblank is not initialized (IRQ not installed ?), or has been freed */
 	if (!drm_dev_has_vblank(dev))
@@ -1561,9 +1560,9 @@ static void drm_legacy_vblank_post_modeset(struct drm_device *dev,
 		return;
 
 	if (vblank->inmodeset) {
-		spin_lock_irqsave(&dev->vbl_lock, irqflags);
+		spin_lock_irq(&dev->vbl_lock);
 		drm_reset_vblank_timestamp(dev, pipe);
-		spin_unlock_irqrestore(&dev->vbl_lock, irqflags);
+		spin_unlock_irq(&dev->vbl_lock);
 
 		if (vblank->inmodeset & 0x2)
 			drm_vblank_put(dev, pipe);
-- 
2.26.2

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[PATCH 4/5] drm/vblank: Use spin_(un)lock_irq() in drm_queue_vblank_event()

[Lyude Paul]

This one's easy - we're already calling kzalloc() in this function, so
we must already be guaranteed to have IRQs enabled when calling this.
So, use the plain _irq() variants of spin_(un)lock() to make this more
obvious.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
---
 drivers/gpu/drm/drm_vblank.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
index 51f2e988205e7..64610070ba473 100644
--- a/drivers/gpu/drm/drm_vblank.c
+++ b/drivers/gpu/drm/drm_vblank.c
@@ -1611,7 +1611,6 @@ static int drm_queue_vblank_event(struct drm_device *dev, unsigned int pipe,
 	struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
 	struct drm_pending_vblank_event *e;
 	ktime_t now;
-	unsigned long flags;
 	u64 seq;
 	int ret;
 
@@ -1633,7 +1632,7 @@ static int drm_queue_vblank_event(struct drm_device *dev, unsigned int pipe,
 			e->event.vbl.crtc_id = crtc->base.id;
 	}
 
-	spin_lock_irqsave(&dev->event_lock, flags);
+	spin_lock_irq(&dev->event_lock);
 
 	/*
 	 * drm_crtc_vblank_off() might have been called after we called
@@ -1670,12 +1669,12 @@ static int drm_queue_vblank_event(struct drm_device *dev, unsigned int pipe,
 		vblwait->reply.sequence = req_seq;
 	}
 
-	spin_unlock_irqrestore(&dev->event_lock, flags);
+	spin_unlock_irq(&dev->event_lock);
 
 	return 0;
 
 err_unlock:
-	spin_unlock_irqrestore(&dev->event_lock, flags);
+	spin_unlock_irq(&dev->event_lock);
 	kfree(e);
 err_put:
 	drm_vblank_put(dev, pipe);
-- 
2.26.2

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[PATCH 5/5] drm/vblank: Use spin_(un)lock_irq() in drm_crtc_queue_sequence_ioctl()

[Lyude Paul]

This is an ioctl callback, so we're guaranteed to have IRQs enabled when
calling this function. Use the plain _irq() variants of spin_(un)lock()
to make this more obvious.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
---
 drivers/gpu/drm/drm_vblank.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
index 64610070ba473..b18e1efbbae1a 100644
--- a/drivers/gpu/drm/drm_vblank.c
+++ b/drivers/gpu/drm/drm_vblank.c
@@ -2066,7 +2066,6 @@ int drm_crtc_queue_sequence_ioctl(struct drm_device *dev, void *data,
 	u64 seq;
 	u64 req_seq;
 	int ret;
-	unsigned long spin_flags;
 
 	if (!drm_core_check_feature(dev, DRIVER_MODESET))
 		return -EOPNOTSUPP;
@@ -2114,7 +2113,7 @@ int drm_crtc_queue_sequence_ioctl(struct drm_device *dev, void *data,
 	e->event.base.length = sizeof(e->event.seq);
 	e->event.seq.user_data = queue_seq->user_data;
 
-	spin_lock_irqsave(&dev->event_lock, spin_flags);
+	spin_lock_irq(&dev->event_lock);
 
 	/*
 	 * drm_crtc_vblank_off() might have been called after we called
@@ -2145,11 +2144,11 @@ int drm_crtc_queue_sequence_ioctl(struct drm_device *dev, void *data,
 		queue_seq->sequence = req_seq;
 	}
 
-	spin_unlock_irqrestore(&dev->event_lock, spin_flags);
+	spin_unlock_irq(&dev->event_lock);
 	return 0;
 
 err_unlock:
-	spin_unlock_irqrestore(&dev->event_lock, spin_flags);
+	spin_unlock_irq(&dev->event_lock);
 	drm_crtc_vblank_put(crtc);
 err_free:
 	kfree(e);
-- 
2.26.2

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Re: [PATCH 4/5] drm/vblank: Use spin_(un)lock_irq() in drm_queue_vblank_event()

[Daniel Vetter]

On Mon, Jul 20, 2020 at 03:07:35PM -0400, Lyude Paul wrote:
> This one's easy - we're already calling kzalloc() in this function, so

Nit: "kzalloc(GFP_KERNEL)", since kzalloc(GFP_ATOMIC) is perfectly fine in
interrupt context. With that clarified for the entire series:

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

> we must already be guaranteed to have IRQs enabled when calling this.
> So, use the plain _irq() variants of spin_(un)lock() to make this more
> obvious.
> 
> Signed-off-by: Lyude Paul <lyude@redhat.com>
> Cc: Daniel Vetter <daniel@ffwll.ch>
> ---
>  drivers/gpu/drm/drm_vblank.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
> index 51f2e988205e7..64610070ba473 100644
> --- a/drivers/gpu/drm/drm_vblank.c
> +++ b/drivers/gpu/drm/drm_vblank.c
> @@ -1611,7 +1611,6 @@ static int drm_queue_vblank_event(struct drm_device *dev, unsigned int pipe,
>  	struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
>  	struct drm_pending_vblank_event *e;
>  	ktime_t now;
> -	unsigned long flags;
>  	u64 seq;
>  	int ret;
>  
> @@ -1633,7 +1632,7 @@ static int drm_queue_vblank_event(struct drm_device *dev, unsigned int pipe,
>  			e->event.vbl.crtc_id = crtc->base.id;
>  	}
>  
> -	spin_lock_irqsave(&dev->event_lock, flags);
> +	spin_lock_irq(&dev->event_lock);
>  
>  	/*
>  	 * drm_crtc_vblank_off() might have been called after we called
> @@ -1670,12 +1669,12 @@ static int drm_queue_vblank_event(struct drm_device *dev, unsigned int pipe,
>  		vblwait->reply.sequence = req_seq;
>  	}
>  
> -	spin_unlock_irqrestore(&dev->event_lock, flags);
> +	spin_unlock_irq(&dev->event_lock);
>  
>  	return 0;
>  
>  err_unlock:
> -	spin_unlock_irqrestore(&dev->event_lock, flags);
> +	spin_unlock_irq(&dev->event_lock);
>  	kfree(e);
>  err_put:
>  	drm_vblank_put(dev, pipe);
> -- 
> 2.26.2
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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