Patch "drm/i915/gvt: Fix inconsistent locks holding sequence" has been added to the 4.12-stable tree

Patch "drm/i915/gvt: Fix inconsistent locks holding sequence" has been added to the 4.12-stable tree

[gregkh]

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

    drm/i915/gvt: Fix inconsistent locks holding sequence

to the 4.12-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-gvt-fix-inconsistent-locks-holding-sequence.patch
and it can be found in the queue-4.12 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From f16bd3dda2c8bf6699e808cd9cc540cfab10e60e Mon Sep 17 00:00:00 2001
From: Chuanxiao Dong <chuanxiao.dong@intel.com>
Date: Mon, 26 Jun 2017 15:20:50 +0800
Subject: drm/i915/gvt: Fix inconsistent locks holding sequence

From: Chuanxiao Dong <chuanxiao.dong@intel.com>

commit f16bd3dda2c8bf6699e808cd9cc540cfab10e60e upstream.

There are two kinds of locking sequence.

One is in the thread which is started by vfio ioctl to do
the iommu unmapping. The locking sequence is:
	down_read(&group_lock) ----> mutex_lock(&cached_lock)

The other is in the vfio release thread which will unpin all
the cached pages. The lock sequence is:
	mutex_lock(&cached_lock) ---> down_read(&group_lock)

And, the cache_lock is used to protect the rb tree of the cache
node and doing vfio unpin doesn't require this lock. Move the
vfio unpin out of the cache_lock protected region.

v2:
- use for style instead of do{}while(1). (Zhenyu)

Fixes: f30437c5e7bf ("drm/i915/gvt: add KVMGT support")
Signed-off-by: Chuanxiao Dong <chuanxiao.dong@intel.com>
Cc: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/gpu/drm/i915/gvt/kvmgt.c |   14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

--- a/drivers/gpu/drm/i915/gvt/kvmgt.c
+++ b/drivers/gpu/drm/i915/gvt/kvmgt.c
@@ -260,16 +260,20 @@ static void gvt_cache_destroy(struct int
 	struct device *dev = mdev_dev(vgpu->vdev.mdev);
 	unsigned long gfn;
 
-	mutex_lock(&vgpu->vdev.cache_lock);
-	while ((node = rb_first(&vgpu->vdev.cache))) {
+	for (;;) {
+		mutex_lock(&vgpu->vdev.cache_lock);
+		node = rb_first(&vgpu->vdev.cache);
+		if (!node) {
+			mutex_unlock(&vgpu->vdev.cache_lock);
+			break;
+		}
 		dma = rb_entry(node, struct gvt_dma, node);
 		gvt_dma_unmap_iova(vgpu, dma->iova);
 		gfn = dma->gfn;
-
-		vfio_unpin_pages(dev, &gfn, 1);
 		__gvt_cache_remove_entry(vgpu, dma);
+		mutex_unlock(&vgpu->vdev.cache_lock);
+		vfio_unpin_pages(dev, &gfn, 1);
 	}
-	mutex_unlock(&vgpu->vdev.cache_lock);
 }
 
 static struct intel_vgpu_type *intel_gvt_find_vgpu_type(struct intel_gvt *gvt,


Patches currently in stable-queue which might be from chuanxiao.dong@intel.com are

queue-4.12/drm-i915-gvt-fix-possible-recursive-locking-issue.patch
queue-4.12/drm-i915-gvt-fix-inconsistent-locks-holding-sequence.patch
queue-4.12/vfio-remove-unnecessary-uses-of-vfio_container.group_lock.patch