[PATCH 05/25] drm/i915: Reorder struct_mutex-vs-reset_lock in i915_gem_fault()

Chris Wilson
2019-02-19T12:22:27Z

Annoyingly, struct_mutex was not entirely eliminated from the reset
pathway; for reasons of its own, intel_display_resumes() requires
struct_mutex to prepare the planes it already captured. To avoid the
immediate problem of a deadlock between the struct_mutex and the reset
srcu, we have to acquire the reset_lock before struct_mutex in
i915_gem_fault(). Now any wait underneath struct_mutex will result us in
having to forcibly reset all inflight rendering, less than ideal.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
---
drivers/gpu/drm/i915/i915_gem.c | 20 ++++++++++----------
1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index b421bc7a2e26..b3129cb0a04d 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1834,9 +1834,15 @@ vm_fault_t i915_gem_fault(struct vm_fault *vmf)

wakeref = intel_runtime_pm_get(dev_priv);

+ srcu = i915_reset_trylock(dev_priv);
+ if (srcu < 0) {
+ ret = srcu;
+ goto err_rpm;
+ }
+
ret = i915_mutex_lock_interruptible(dev);
if (ret)
- goto err_rpm;
+ goto err_reset;

/* Access to snoopable pages through the GTT is incoherent. */
if (obj->cache_level != I915_CACHE_NONE && !HAS_LLC(dev_priv)) {
@@ -1885,12 +1891,6 @@ vm_fault_t i915_gem_fault(struct vm_fault *vmf)
if (ret)
goto err_unpin;

- srcu = i915_reset_trylock(dev_priv);
- if (srcu < 0) {
- ret = srcu;
- goto err_fence;
- }
-
/* Finally, remap it using the new GTT offset */
ret = remap_io_mapping(area,
area->vm_start + (vma->ggtt_view.partial.offset << PAGE_SHIFT),
@@ -1898,7 +1898,7 @@ vm_fault_t i915_gem_fault(struct vm_fault *vmf)
min_t(u64, vma->size, area->vm_end - area->vm_start),
&ggtt->iomap);
if (ret)
- goto err_reset;
+ goto err_fence;

/* Mark as being mmapped into userspace for later revocation */
assert_rpm_wakelock_held(dev_priv);
@@ -1908,14 +1908,14 @@ vm_fault_t i915_gem_fault(struct vm_fault *vmf)

i915_vma_set_ggtt_write(vma);

-err_reset:
- i915_reset_unlock(dev_priv, srcu);
err_fence:
i915_vma_unpin_fence(vma);
err_unpin:
__i915_vma_unpin(vma);
err_unlock:
mutex_unlock(&dev->struct_mutex);
+err_reset:
+ i915_reset_unlock(dev_priv, srcu);
err_rpm:
intel_runtime_pm_put(dev_priv, wakeref);
i915_gem_object_unpin_pages(obj);