drm/i915: Reorder struct_mutex-vs-reset_lock in i915_gem_fault()

Annoyingly, struct_mutex was not entirely eliminated from the reset
pathway; for reasons of its own, intel_display_resume() 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, but
better than a deadlock (and will do for the short term).

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190221102924.13442-1-chris@chris-wilson.co.uk

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index cc88e7974422c9e396779f03d905a4545efea331..62e4df1cbf87429bafc0bca2c5cc1e4cdec53b16 100644 (file)
--- 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);