[PATCH 1/7] drm/i915: Untangle the vma pages_mutex

From: "Thomas Hellström" <thomas.hellstrom@linux.intel.com>
To: intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org
Cc: "Thomas Hellström" <thomas.hellstrom@intel.com>
Subject: [PATCH 1/7] drm/i915: Untangle the vma pages_mutex
Date: Tue, 11 May 2021 15:25:19 +0200	[thread overview]
Message-ID: <20210511132525.377190-2-thomas.hellstrom@linux.intel.com> (raw)
In-Reply-To: <20210511132525.377190-1-thomas.hellstrom@linux.intel.com>

From: Thomas Hellström <thomas.hellstrom@intel.com>

Any sleeping dma_resv lock taken while the vma pages_mutex is held
will cause a lockdep splat.
Move the i915_gem_object_pin_pages() call out of the pages_mutex
critical section.

Signed-off-by: Thomas Hellström <thomas.hellstrom@intel.com>
---
 drivers/gpu/drm/i915/i915_vma.c | 33 +++++++++++++++++++--------------
 1 file changed, 19 insertions(+), 14 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
index a6cd0fa62847..7b1c0f4e60d7 100644
--- a/drivers/gpu/drm/i915/i915_vma.c
+++ b/drivers/gpu/drm/i915/i915_vma.c
@@ -800,32 +800,37 @@ static bool try_qad_pin(struct i915_vma *vma, unsigned int flags)
 static int vma_get_pages(struct i915_vma *vma)
 {
 	int err = 0;
+	bool pinned_pages = false;
 
 	if (atomic_add_unless(&vma->pages_count, 1, 0))
 		return 0;
 
+	if (vma->obj) {
+		err = i915_gem_object_pin_pages(vma->obj);
+		if (err)
+			return err;
+		pinned_pages = true;
+	}
+
 	/* Allocations ahoy! */
-	if (mutex_lock_interruptible(&vma->pages_mutex))
-		return -EINTR;
+	if (mutex_lock_interruptible(&vma->pages_mutex)) {
+		err = -EINTR;
+		goto unpin;
+	}
 
 	if (!atomic_read(&vma->pages_count)) {
-		if (vma->obj) {
-			err = i915_gem_object_pin_pages(vma->obj);
-			if (err)
-				goto unlock;
-		}
-
 		err = vma->ops->set_pages(vma);
-		if (err) {
-			if (vma->obj)
-				i915_gem_object_unpin_pages(vma->obj);
+		if (err)
 			goto unlock;
-		}
+		pinned_pages = false;
 	}
 	atomic_inc(&vma->pages_count);
 
 unlock:
 	mutex_unlock(&vma->pages_mutex);
+unpin:
+	if (pinned_pages)
+		__i915_gem_object_unpin_pages(vma->obj);
 
 	return err;
 }
@@ -838,10 +843,10 @@ static void __vma_put_pages(struct i915_vma *vma, unsigned int count)
 	if (atomic_sub_return(count, &vma->pages_count) == 0) {
 		vma->ops->clear_pages(vma);
 		GEM_BUG_ON(vma->pages);
-		if (vma->obj)
-			i915_gem_object_unpin_pages(vma->obj);
 	}
 	mutex_unlock(&vma->pages_mutex);
+	if (vma->obj)
+		i915_gem_object_unpin_pages(vma->obj);
 }
 
 static void vma_put_pages(struct i915_vma *vma)
-- 
2.30.2

