drm/nouveau: fix relocations applying logic and a double-free

Commit 03e0d26f ("drm/nouveau: slowpath for pushbuf ioctl") included
a logic-bug which results in the relocations not actually getting
applied at all as the call to nouveau_gem_pushbuf_reloc_apply() is
never reached. This causes a regression with graphical corruption,
triggered when relocations need to be done (for example after a
suspend/resume cycle.)

Fix by setting *apply_relocs value only if there were more than 0
relocations.

Additionally, the never reached code had a leftover u_free() call,
which, after fixing the logic, now got called and resulted in a
double-free. Fix by removing one u_free(), moving the other
and adding check for errors.

Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Ben Skeggs <bskeggs@redhat.com>
Cc: nouveau@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Matti Hamalainen <ccr@tnsp.org>
Fixes: 03e0d26f ("drm/nouveau: slowpath for pushbuf ioctl")
References: https://gitlab.freedesktop.org/drm/nouveau/-/issues/11Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20201120152338.1203257-1-ccr@tnsp.org

drivers/gpu/drm/nouveau/nouveau_gem.c

@@ -558,8 +558,10 @@ nouveau_gem_pushbuf_validate(struct nouveau_channel *chan,
 			NV_PRINTK(err, cli, "validating bo list\n");
 		validate_fini(op, chan, NULL, NULL);
 		return ret;
+	} else if (ret > 0) {
+		*apply_relocs = true;
 	}
-	*apply_relocs = ret;
+
 	return 0;
 }
 
@@ -662,7 +664,6 @@ nouveau_gem_pushbuf_reloc_apply(struct nouveau_cli *cli,
 		nouveau_bo_wr32(nvbo, r->reloc_bo_offset >> 2, data);
 	}
 
-	u_free(reloc);
 	return ret;
 }
 
@@ -872,9 +873,10 @@ nouveau_gem_ioctl_pushbuf(struct drm_device *dev, void *data,
 				break;
 			}
 		}
-		u_free(reloc);
 	}
 out_prevalid:
+	if (!IS_ERR(reloc))
+		u_free(reloc);
 	u_free(bo);
 	u_free(push);