[3.11.y.z extended stable] Patch "drm/i915: Flush outstanding requests before allocating new seqno" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    drm/i915: Flush outstanding requests before allocating new seqno

to the linux-3.11.y-queue branch of the 3.11.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.11.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.11.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 46945654c14920a8a8491630e494416a42c5d180 Mon Sep 17 00:00:00 2001
From: Chris Wilson <chris at chris-wilson.co.uk>
Date: Thu, 2 Jan 2014 14:32:35 +0000
Subject: drm/i915: Flush outstanding requests before allocating new seqno

commit 304d695c3dc8eb65206b9eaf16f8d1a41510d1cf upstream.

In very rare cases (such as a memory failure stress test) it is possible
to fill the entire ring without emitting a request. Under this
circumstance, the outstanding request is flushed and waited upon. After
space on the ring is cleared, we return to emitting the new command -
except that we just cleared the seqno allocated for this operation and
trigger the sanity check that a request is only ever emitted with a
valid seqno. The fix is to rearrange the code to make sure the
allocation of the seqno for this operation is after any required flushes
of outstanding operations.

The bug exists since the preallocation was introduced in
commit 9d7730914f4cd496e356acfab95b41075aa8eae8
Author: Chris Wilson <chris at chris-wilson.co.uk>
Date:   Tue Nov 27 16:22:52 2012 +0000

    drm/i915: Preallocate next seqno before touching the ring

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala at intel.com>
Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Reviewed-by: Jani Nikula <jani.nikula at intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/gpu/drm/i915/intel_ringbuffer.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 079ef01..9e171c2 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -1557,8 +1557,8 @@ intel_ring_alloc_seqno(struct intel_ring_buffer *ring)
 	return i915_gem_get_seqno(ring->dev, &ring->outstanding_lazy_request);
 }

-static int __intel_ring_begin(struct intel_ring_buffer *ring,
-			      int bytes)
+static int __intel_ring_prepare(struct intel_ring_buffer *ring,
+				int bytes)
 {
 	int ret;

@@ -1574,7 +1574,6 @@ static int __intel_ring_begin(struct intel_ring_buffer *ring,
 			return ret;
 	}

-	ring->space -= bytes;
 	return 0;
 }

@@ -1589,12 +1588,17 @@ int intel_ring_begin(struct intel_ring_buffer *ring,
 	if (ret)
 		return ret;

+	ret = __intel_ring_prepare(ring, num_dwords * sizeof(uint32_t));
+	if (ret)
+		return ret;
+
 	/* Preallocate the olr before touching the ring */
 	ret = intel_ring_alloc_seqno(ring);
 	if (ret)
 		return ret;

-	return __intel_ring_begin(ring, num_dwords * sizeof(uint32_t));
+	ring->space -= num_dwords * sizeof(uint32_t);
+	return 0;
 }

 void intel_ring_init_seqno(struct intel_ring_buffer *ring, u32 seqno)
--
1.8.3.2