drm/ttm: Fix a theoretical race in ttm_bo_cleanup_refs()

In theory, that function could release the lru lock between
checking for bo on ddestroy list and a successful reserve if the bo
was already reserved, and the function was called with waiting reserves
allowed.
However, all current reservers of a bo on the ddestroy list would
atomically take the bo off the list after a successful reserve so this
race should not have been hit, so no need to backport for stable.

This patch also fixes a case found by Maarten Lankhorst where
ttm_mem_evict_first called with no_wait_gpu would incorrectly
spin waiting for bo idle if trying to evict a busy buffer that
also sits on the ddestroy list.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

1 files changed, 12 insertions, 8 deletions

diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
index d42631cade5a..bf6e4b5a73b5 100644
--- a/drivers/gpu/drm/ttm/ttm_bo.c
+++ b/drivers/gpu/drm/ttm/ttm_bo.c
@@ -580,6 +580,7 @@ retry:
         if (unlikely(ret != 0))
                 return ret;
 
+retry_reserve:
         spin_lock(&glob->lru_lock);
 
         if (unlikely(list_empty(&bo->ddestroy))) {
@@ -587,14 +588,20 @@ retry:
                 return 0;
         }
 
-        ret = ttm_bo_reserve_locked(bo, interruptible,
-                                    no_wait_reserve, false, 0);
+        ret = ttm_bo_reserve_locked(bo, false, true, false, 0);
 
-        if (unlikely(ret != 0)) {
+        if (unlikely(ret == -EBUSY)) {
                 spin_unlock(&glob->lru_lock);
-                return ret;
+                if (likely(!no_wait_reserve))
+                        ret = ttm_bo_wait_unreserved(bo, interruptible);
+                if (unlikely(ret != 0))
+                        return ret;
+
+                goto retry_reserve;
         }
 
+        BUG_ON(ret != 0);
+
         /**
          * We can re-check for sync object without taking
          * the bo::lock since setting the sync object requires
@@ -811,10 +818,7 @@ retry:
                                           no_wait_reserve, no_wait_gpu);
                 kref_put(&bo->list_kref, ttm_bo_release_list);
 
-                if (likely(ret == 0 || ret == -ERESTARTSYS))
-                        return ret;
-
-                goto retry;
+                return ret;
         }
 
         ret = ttm_bo_reserve_locked(bo, false, true, false, 0);