Patch "drm/i915: Always mark the object as dirty when used by the GPU" has been added to the 4.2-stable tree

This is a note to let you know that I've just added the patch titled

drm/i915: Always mark the object as dirty when used by the GPU

to the 4.2-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
drm-i915-always-mark-the-object-as-dirty-when-used-by-the-gpu.patch
and it can be found in the queue-4.2 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Chris Wilson <[email protected]>
Date: Mon, 31 Aug 2015 15:10:39 +0100
Subject: drm/i915: Always mark the object as dirty when used by the GPU
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From: Chris Wilson <[email protected]>

commit 51bc140431e233284660b1d22c47dec9ecdb521e upstream.

There have been many hard to track down bugs whereby userspace forgot to flag a write buffer and then cause graphics corruption or a hung GPU when that buffer was later purged under memory pressure (as the buffer appeared clean, its pages would have been evicted rather than preserved and any changes more recent than in the backing storage would be lost). In retrospect this is a rare optimisation against memory pressure, already the slow path. If we always mark the buffer as dirty when accessed by the GPU, anything not used can still be evicted cheaply (ideal behaviour for mark-and-sweep eviction) but we do not run the risk of corruption. For correct read serialisation, userspace still has to notify when the GPU writes to an object. However, there are certain situations under which userspace may wish to tell white lies to the kernel...

---
 drivers/gpu/drm/i915/i915_gem_execbuffer.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

@@ -1024,6 +1024,7 @@ i915_gem_execbuffer_move_to_active(struc
 		u32 old_read = obj->base.read_domains;
 		u32 old_write = obj->base.write_domain;
 
+		obj->dirty = 1; /* be paranoid  */
 		obj->base.write_domain = obj->base.pending_write_domain;
 		if (obj->base.write_domain == 0)
 			obj->base.pending_read_domains |= obj->base.read_domains;

@@ -1031,7 +1032,6 @@ i915_gem_execbuffer_move_to_active(struc
 
 		i915_vma_move_to_active(vma, ring);
 		if (obj->base.write_domain) {
-			obj->dirty = 1;
 			i915_gem_request_assign(&obj->last_write_req, req);
 
 			intel_fb_obj_invalidate(obj, ring, ORIGIN_CS);

Patches currently in stable-queue which might be from [email protected] are

queue-4.2/drm-i915-always-mark-the-object-as-dirty-when-used-by-the-gpu.patch