nouveau: make nouveau importing global buffers completely thread-safe, with tests

While I've closed off most races in a previous patch, a small race still existed
where importing then unreffing cound cause an invalid bo. Add a test for this case.

Racing sequence fixed:

- thread 1 releases bo, refcount drops to zero, blocks on acquiring nvdev->lock.
- thread 2 increases refcount to 1.
- thread 2 decreases refcount to zero, blocks on acquiring nvdev->lock.

At this point the 2 threads will clean up the same bo.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@ubuntu.com>
Reviewed-By: Emil Velikov <emil.l.velikov@gmail.com>

configure.ac

@@ -454,6 +454,7 @@ AC_CONFIG_FILES([
 	tests/vbltest/Makefile
 	tests/exynos/Makefile
 	tests/tegra/Makefile
+	tests/nouveau/Makefile
 	man/Makefile
 	libdrm.pc])
 AC_OUTPUT

nouveau/nouveau.c

@@ -351,29 +351,18 @@ nouveau_bo_del(struct nouveau_bo *bo)
 
 	pthread_mutex_lock(&nvdev->lock);
 	if (nvbo->name) {
-		if (atomic_read(&nvbo->refcnt)) {
-			/*
-			 * bo has been revived by a race with
-			 * nouveau_bo_prime_handle_ref, or nouveau_bo_name_ref.
-			 *
-			 * In theory there's still a race possible with
-			 * nouveau_bo_wrap, but when using this function
-			 * the lifetime of the handle is probably already
-			 * handled in another way. If there are races
-			 * you're probably using nouveau_bo_wrap wrong.
-			 */
-			pthread_mutex_unlock(&nvdev->lock);
-			return;
-		}
+		if (atomic_read(&nvbo->refcnt) == 0) {
 			DRMLISTDEL(&nvbo->head);
 			/*
-		 * This bo has to be closed with the lock held because gem
-		 * handles are not refcounted. If a shared bo is closed and
-		 * re-opened in another thread a race against
-		 * DRM_IOCTL_GEM_OPEN or drmPrimeFDToHandle might cause the
-		 * bo to be closed accidentally while re-importing.
+			 * This bo has to be closed with the lock held because
+			 * gem handles are not refcounted. If a shared bo is
+			 * closed and re-opened in another thread a race
+			 * against DRM_IOCTL_GEM_OPEN or drmPrimeFDToHandle
+			 * might cause the bo to be closed accidentally while
+			 * re-importing.
 			 */
 			drmIoctl(bo->device->fd, DRM_IOCTL_GEM_CLOSE, &req);
+		}
 		pthread_mutex_unlock(&nvdev->lock);
 	} else {
 		DRMLISTDEL(&nvbo->head);
@@ -418,7 +407,7 @@ nouveau_bo_new(struct nouveau_device *dev, uint32_t flags, uint32_t align,
 
 static int
 nouveau_bo_wrap_locked(struct nouveau_device *dev, uint32_t handle,
-		       struct nouveau_bo **pbo)
+		       struct nouveau_bo **pbo, int name)
 {
 	struct nouveau_device_priv *nvdev = nouveau_device(dev);
 	struct drm_nouveau_gem_info req = { .handle = handle };
@@ -427,8 +416,24 @@ nouveau_bo_wrap_locked(struct nouveau_device *dev, uint32_t handle,
 
 	DRMLISTFOREACHENTRY(nvbo, &nvdev->bo_list, head) {
 		if (nvbo->base.handle == handle) {
-			*pbo = NULL;
-			nouveau_bo_ref(&nvbo->base, pbo);
+			if (atomic_inc_return(&nvbo->refcnt) == 1) {
+				/*
+				 * Uh oh, this bo is dead and someone else
+				 * will free it, but because refcnt is
+				 * now non-zero fortunately they won't
+				 * call the ioctl to close the bo.
+				 *
+				 * Remove this bo from the list so other
+				 * calls to nouveau_bo_wrap_locked will
+				 * see our replacement nvbo.
+				 */
+				DRMLISTDEL(&nvbo->head);
+				if (!name)
+					name = nvbo->name;
+				break;
+			}
+
+			*pbo = &nvbo->base;
 			return 0;
 		}
 	}
@@ -443,6 +448,7 @@ nouveau_bo_wrap_locked(struct nouveau_device *dev, uint32_t handle,
 		atomic_set(&nvbo->refcnt, 1);
 		nvbo->base.device = dev;
 		abi16_bo_info(&nvbo->base, &req);
+		nvbo->name = name;
 		DRMLISTADD(&nvbo->head, &nvdev->bo_list);
 		*pbo = &nvbo->base;
 		return 0;
@@ -458,7 +464,7 @@ nouveau_bo_wrap(struct nouveau_device *dev, uint32_t handle,
 	struct nouveau_device_priv *nvdev = nouveau_device(dev);
 	int ret;
 	pthread_mutex_lock(&nvdev->lock);
-	ret = nouveau_bo_wrap_locked(dev, handle, pbo);
+	ret = nouveau_bo_wrap_locked(dev, handle, pbo, 0);
 	pthread_mutex_unlock(&nvdev->lock);
 	return ret;
 }
@@ -468,24 +474,13 @@ nouveau_bo_name_ref(struct nouveau_device *dev, uint32_t name,
 		    struct nouveau_bo **pbo)
 {
 	struct nouveau_device_priv *nvdev = nouveau_device(dev);
-	struct nouveau_bo_priv *nvbo;
 	struct drm_gem_open req = { .name = name };
 	int ret;
 
 	pthread_mutex_lock(&nvdev->lock);
-	DRMLISTFOREACHENTRY(nvbo, &nvdev->bo_list, head) {
-		if (nvbo->name == name) {
-			*pbo = NULL;
-			nouveau_bo_ref(&nvbo->base, pbo);
-			pthread_mutex_unlock(&nvdev->lock);
-			return 0;
-		}
-	}
-
 	ret = drmIoctl(dev->fd, DRM_IOCTL_GEM_OPEN, &req);
 	if (ret == 0) {
-		ret = nouveau_bo_wrap_locked(dev, req.handle, pbo);
-		nouveau_bo((*pbo))->name = name;
+		ret = nouveau_bo_wrap_locked(dev, req.handle, pbo, name);
 	}
 
 	pthread_mutex_unlock(&nvdev->lock);
@@ -537,7 +532,7 @@ nouveau_bo_prime_handle_ref(struct nouveau_device *dev, int prime_fd,
 	pthread_mutex_lock(&nvdev->lock);
 	ret = drmPrimeFDToHandle(dev->fd, prime_fd, &handle);
 	if (ret == 0) {
-		ret = nouveau_bo_wrap_locked(dev, handle, bo);
+		ret = nouveau_bo_wrap_locked(dev, handle, bo, 0);
 		if (!ret) {
 			struct nouveau_bo_priv *nvbo = nouveau_bo(*bo);
 			if (!nvbo->name) {

tests/Makefile.am

@@ -31,6 +31,10 @@ check_PROGRAMS = \
 	dristat \
 	drmstat
 
+if HAVE_NOUVEAU
+SUBDIRS += nouveau
+endif
+
 if HAVE_LIBUDEV
 
 check_LTLIBRARIES = libdrmtest.la

tests/nouveau/.gitignore

@@ -0,0 +1 @@
+threaded

tests/nouveau/Makefile.am

@@ -0,0 +1,16 @@
+AM_CPPFLAGS = \
+	-I$(top_srcdir)/include/drm \
+	-I$(top_srcdir)/nouveau \
+	-I$(top_srcdir)
+
+AM_CFLAGS = $(WARN_CFLAGS)
+
+LDADD = \
+	../../nouveau/libdrm_nouveau.la \
+	../../libdrm.la \
+	-ldl -lpthread
+
+TESTS = threaded
+
+check_PROGRAMS = $(TESTS)
+

tests/nouveau/threaded.c

@@ -0,0 +1,156 @@
+/*
+ * Copyright © 2015 Canonical Ltd. (Maarten Lankhorst)
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR
+ * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
+ * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+ * OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+#ifdef HAVE_CONFIG_H
+#  include "config.h"
+#endif
+
+#include <sys/ioctl.h>
+#include <dlfcn.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <errno.h>
+#include <pthread.h>
+
+#include "xf86drm.h"
+#include "nouveau.h"
+
+static typeof(ioctl) *old_ioctl;
+static int failed;
+
+static int import_fd;
+
+int ioctl(int fd, unsigned long request, ...)
+{
+	va_list va;
+	int ret;
+	void *arg;
+
+	va_start(va, request);
+	arg = va_arg(va, void *);
+	ret = old_ioctl(fd, request, arg);
+	va_end(va);
+
+	if (ret < 0 && request == DRM_IOCTL_GEM_CLOSE && errno == EINVAL)
+		failed = 1;
+
+	return ret;
+}
+
+static void *
+openclose(void *dev)
+{
+	struct nouveau_device *nvdev = dev;
+	struct nouveau_bo *bo = NULL;
+	int i;
+
+	for (i = 0; i < 100000; ++i) {
+		if (!nouveau_bo_prime_handle_ref(nvdev, import_fd, &bo))
+			nouveau_bo_ref(NULL, &bo);
+	}
+	return NULL;
+}
+
+int main(int argc, char *argv[])
+{
+	drmVersionPtr version;
+	const char *device = NULL;
+	int err, fd, fd2;
+	struct nouveau_device *nvdev, *nvdev2;
+	struct nouveau_bo *bo;
+	pthread_t t1, t2;
+
+	old_ioctl = dlsym(RTLD_NEXT, "ioctl");
+
+	if (argc < 2) {
+		fd = drmOpenWithType("nouveau", NULL, DRM_NODE_RENDER);
+		if (fd >= 0)
+			fd2 = drmOpenWithType("nouveau", NULL, DRM_NODE_RENDER);
+	} else {
+		device = argv[1];
+
+		fd = open(device, O_RDWR);
+		if (fd >= 0)
+			fd2 = open(device, O_RDWR);
+		else
+			fd2 = fd = -errno;
+	}
+
+	if (fd < 0) {
+		fprintf(stderr, "Opening nouveau render node failed with %i\n", fd);
+		return device ? -fd : 77;
+	}
+
+	if (fd2 < 0) {
+		fprintf(stderr, "Opening second nouveau render node failed with %i\n", -errno);
+		return errno;
+	}
+
+	version = drmGetVersion(fd);
+	if (version) {
+		printf("Version: %d.%d.%d\n", version->version_major,
+		       version->version_minor, version->version_patchlevel);
+		printf("  Name: %s\n", version->name);
+		printf("  Date: %s\n", version->date);
+		printf("  Description: %s\n", version->desc);
+
+		drmFreeVersion(version);
+	}
+
+	err = nouveau_device_wrap(fd, 0, &nvdev);
+	if (!err)
+		err = nouveau_device_wrap(fd2, 0, &nvdev2);
+	if (err < 0)
+		return 1;
+
+	err = nouveau_bo_new(nvdev2, NOUVEAU_BO_GART, 0, 4096, NULL, &bo);
+	if (!err)
+		err = nouveau_bo_set_prime(bo, &import_fd);
+
+	if (!err) {
+		pthread_create(&t1, NULL, openclose, nvdev);
+		pthread_create(&t2, NULL, openclose, nvdev);
+	}
+
+	pthread_join(t1, NULL);
+	pthread_join(t2, NULL);
+
+	close(import_fd);
+	nouveau_bo_ref(NULL, &bo);
+
+	nouveau_device_del(&nvdev2);
+	nouveau_device_del(&nvdev);
+	if (device) {
+		close(fd2);
+		close(fd);
+	} else {
+		drmClose(fd2);
+		drmClose(fd);
+	}
+
+	if (failed)
+		fprintf(stderr, "DRM_IOCTL_GEM_CLOSE failed with EINVAL,\n"
+				"race in opening/closing bo is likely.\n");
+
+	return failed;
+}