Re: [PATCH 1/1 repost #1] DRM: don't enable irqs in locking

["Thomas Hellström" <thomas@tungstengraphics.com>]

[-- Attachment #1: Type: text/plain, Size: 438 bytes --]

Johannes Engel wrote:
> Thomas Hellström wrote:
>> Yes, this bug could occur, but the remedy is not to use 
>> spin_lock_irqsave() for lock_data::spinlock but to avoid calling 
>> drm_lock_take with the drm_device::tasklet_lock held with irqs disabled.
>> I'll see if I can come up with a patch.
> Hi Thomas,
>
> any news on that so far?
>
> Cheers, Johannes
Hi!
Been on vacation.

Pls try the attached patch.

/Thomas


[-- Attachment #2: 0001-Don-t-call-the-vblank-tasklet-with-irqs-disabled.patch --]
[-- Type: text/plain, Size: 2775 bytes --]

>From af12ef4f6b4ca111d9a2ef45263ad89610498724 Mon Sep 17 00:00:00 2001
From: Thomas Hellstrom <thomas-at-tungstengraphics-dot-com>
Date: Wed, 13 Aug 2008 10:04:21 +0200
Subject: [PATCH] Don't call the vblank tasklet with irqs disabled.
 If a specific tasklet shares data with irq context,
 it needs to take a private irq-blocking spinlock within
 the tasklet itself.


Signed-off-by: Thomas Hellstrom <thomas-at-tungstengraphics-dot-com>
---
 linux-core/drm_irq.c  |   20 ++++++++++++--------
 linux-core/drm_lock.c |   12 +++++-------
 2 files changed, 17 insertions(+), 15 deletions(-)

diff --git a/linux-core/drm_irq.c b/linux-core/drm_irq.c
index 5b9f474..57419ca 100644
--- a/linux-core/drm_irq.c
+++ b/linux-core/drm_irq.c
@@ -705,27 +705,31 @@ static void drm_locked_tasklet_func(unsigned long data)
 {
 	struct drm_device *dev = (struct drm_device *)data;
 	unsigned long irqflags;
-
+	void (*tasklet_func)(struct drm_device *);
+	
 	spin_lock_irqsave(&dev->tasklet_lock, irqflags);
+	tasklet_func = dev->locked_tasklet_func;
+	spin_unlock_irqrestore(&dev->tasklet_lock, irqflags);
 
-	if (!dev->locked_tasklet_func ||
+	if (!tasklet_func ||
 	    !drm_lock_take(&dev->lock,
 			   DRM_KERNEL_CONTEXT)) {
-		spin_unlock_irqrestore(&dev->tasklet_lock, irqflags);
 		return;
 	}
 
 	dev->lock.lock_time = jiffies;
 	atomic_inc(&dev->counts[_DRM_STAT_LOCKS]);
 
-	dev->locked_tasklet_func(dev);
+	spin_lock_irqsave(&dev->tasklet_lock, irqflags);
+	tasklet_func = dev->locked_tasklet_func;
+	dev->locked_tasklet_func = NULL;
+	spin_unlock_irqrestore(&dev->tasklet_lock, irqflags);
+	
+	if (tasklet_func != NULL)
+		tasklet_func(dev);
 
 	drm_lock_free(&dev->lock,
 		      DRM_KERNEL_CONTEXT);
-
-	dev->locked_tasklet_func = NULL;
-
-	spin_unlock_irqrestore(&dev->tasklet_lock, irqflags);
 }
 
 /**
diff --git a/linux-core/drm_lock.c b/linux-core/drm_lock.c
index a2966ef..cad2e44 100644
--- a/linux-core/drm_lock.c
+++ b/linux-core/drm_lock.c
@@ -155,6 +155,7 @@ int drm_unlock(struct drm_device *dev, void *data, struct drm_file *file_priv)
 {
 	struct drm_lock *lock = data;
 	unsigned long irqflags;
+	void (*tasklet_func)(struct drm_device *);
 
 	if (lock->context == DRM_KERNEL_CONTEXT) {
 		DRM_ERROR("Process %d using kernel context %d\n",
@@ -163,14 +164,11 @@ int drm_unlock(struct drm_device *dev, void *data, struct drm_file *file_priv)
 	}
 
 	spin_lock_irqsave(&dev->tasklet_lock, irqflags);
-
-	if (dev->locked_tasklet_func) {
-		dev->locked_tasklet_func(dev);
-
-		dev->locked_tasklet_func = NULL;
-	}
-
+	tasklet_func = dev->locked_tasklet_func;
+	dev->locked_tasklet_func = NULL;
 	spin_unlock_irqrestore(&dev->tasklet_lock, irqflags);
+	if (tasklet_func != NULL)
+		tasklet_func(dev);
 
 	atomic_inc(&dev->counts[_DRM_STAT_UNLOCKS]);
 
-- 
1.5.4.3