Re: [PATCH 1/2] nouveau: make nouveau importing global buffers completely thread-safe, with tests

[Maarten Lankhorst <maarten.lankhorst-Z7WLFzj8eWMS+FvcfC7Uqw@public.gmane.org>]

On 25-02-15 15:14, Emil Velikov wrote:
> On 24 February 2015 at 09:01, Maarten Lankhorst
> <maarten.lankhorst@ubuntu.com> wrote:
>> 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.
>>
>> How is this fixed? When thread 2 increases refcount to 1 it removes
>> the bo from the list, and creates a new bo. The original thread
>> will notice refcount was increased to 1 and skip deletion from list
>> and closing the handle.
>>
>> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@ubuntu.com>
>> ---
>>  configure.ac              |   1 +
>>  nouveau/nouveau.c         |  69 +++++++++++------------
>>  tests/Makefile.am         |   4 ++
>>  tests/nouveau/.gitignore  |   1 +
>>  tests/nouveau/Makefile.am |  15 +++++
>>  tests/nouveau/threaded.c  | 140 ++++++++++++++++++++++++++++++++++++++++++++++
>>  xf86atomic.h              |   6 +-
>>  7 files changed, 198 insertions(+), 38 deletions(-)
>>  create mode 100644 tests/nouveau/.gitignore
>>  create mode 100644 tests/nouveau/Makefile.am
>>  create mode 100644 tests/nouveau/threaded.c
>>
>> diff --git a/configure.ac b/configure.ac
>> index 8afee83..6dc5044 100644
>> --- a/configure.ac
>> +++ b/configure.ac
>> @@ -441,6 +441,7 @@ AC_CONFIG_FILES([
>>         tests/vbltest/Makefile
>>         tests/exynos/Makefile
>>         tests/tegra/Makefile
>> +       tests/nouveau/Makefile
>>         man/Makefile
>>         libdrm.pc])
>>  AC_OUTPUT
>> diff --git a/nouveau/nouveau.c b/nouveau/nouveau.c
>> index c6c153a..1c723b9 100644
>> --- a/nouveau/nouveau.c
>> +++ b/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)) {
>> +               if (atomic_read(&nvbo->refcnt) == 0) {
>> +                       DRMLISTDEL(&nvbo->head);
>>                         /*
>> -                        * 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.
>> +                        * 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.
>>                          */
>> -                       pthread_mutex_unlock(&nvdev->lock);
>> -                       return;
>> +                       drmIoctl(bo->device->fd, DRM_IOCTL_GEM_CLOSE, &req);
>>                 }
>> -               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.
>> -                */
>> -               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) {
>> diff --git a/tests/Makefile.am b/tests/Makefile.am
>> index 37b8d3a..38e4094 100644
>> --- a/tests/Makefile.am
>> +++ b/tests/Makefile.am
>> @@ -28,6 +28,10 @@ if HAVE_TEGRA
>>  SUBDIRS += tegra
>>  endif
>>
>> +if HAVE_NOUVEAU
>> +SUBDIRS += nouveau
>> +endif
>> +
>>  if HAVE_LIBUDEV
>>
>>  check_LTLIBRARIES = libdrmtest.la
>> diff --git a/tests/nouveau/.gitignore b/tests/nouveau/.gitignore
>> new file mode 100644
>> index 0000000..837bfb9
>> --- /dev/null
>> +++ b/tests/nouveau/.gitignore
>> @@ -0,0 +1 @@
>> +threaded
>> diff --git a/tests/nouveau/Makefile.am b/tests/nouveau/Makefile.am
>> new file mode 100644
>> index 0000000..8e3392e
>> --- /dev/null
>> +++ b/tests/nouveau/Makefile.am
>> @@ -0,0 +1,15 @@
>> +AM_CPPFLAGS = \
>> +       -I$(top_srcdir)/include/drm \
>> +       -I$(top_srcdir)/nouveau \
>> +       -I$(top_srcdir)
>> +
>> +AM_CFLAGS = -Wall -Werror
> Please use $(WARN_CFLAGS)
> 
>> +AM_LDFLAGS = -pthread
>> +
> I assume that adding -lpthread to the LDADD below will be better, but
> I'm not 100% sure.
> 
>> +LDADD = -ldl \
>> +       ../../nouveau/libdrm_nouveau.la \
>> +       ../../libdrm.la
>> +
> Move -ldl at the bottom of the list so that it doesn't bite us in the future.
Ok might be useful indeed.

>> +noinst_PROGRAMS = \
>> +       threaded
> If you want you can add this to the installed tests, and/or make check
make check might fail if nouveau is not found or no render nodes are available, I'd have to add a skip then.

>> +
>> diff --git a/tests/nouveau/threaded.c b/tests/nouveau/threaded.c
>> new file mode 100644
>> index 0000000..490a7fa
>> --- /dev/null
>> +++ b/tests/nouveau/threaded.c
>> @@ -0,0 +1,140 @@
>> +/*
>> + * 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 const char default_device[] = "/dev/dri/renderD128";
>> +
> Reuse the defines in xf86drm.h ?

Hmm, switching to drmOpenWithType("nouveau", NULL, DRM_NODE_RENDER) might be better..

>> +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;
>> +       int err, fd, fd2;
>> +       struct nouveau_device *nvdev, *nvdev2;
>> +       struct nouveau_bo *bo;
>> +
>> +       old_ioctl = dlsym(RTLD_NEXT, "ioctl");
>> +
>> +       pthread_t t1, t2;
>> +
>> +       if (argc < 2)
>> +               device = default_device;
>> +       else
>> +               device = argv[1];
>> +
>> +       fd = open(device, O_RDWR);
>> +       fd2 = open(device, O_RDWR);
>> +       if (fd < 0 || fd2 < 0)
>> +               return 1;
>> +
>> +       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);
>> +       close(fd2);
>> +       close(fd);
>> +
>> +       if (failed)
>> +               fprintf(stderr, "DRM_IOCTL_GEM_CLOSE failed with EINVAL,\n"
>> +                               "race in opening/closing bo is likely.\n");
>> +
>> +       return failed;
>> +}
>> diff --git a/xf86atomic.h b/xf86atomic.h
>> index 8c4b696..66a8d9a 100644
>> --- a/xf86atomic.h
>> +++ b/xf86atomic.h
>> @@ -49,7 +49,8 @@ typedef struct {
>>  # define atomic_read(x) ((x)->atomic)
>>  # define atomic_set(x, val) ((x)->atomic = (val))
>>  # define atomic_inc(x) ((void) __sync_fetch_and_add (&(x)->atomic, 1))
>> -# define atomic_dec_and_test(x) (__sync_fetch_and_add (&(x)->atomic, -1) == 1)
>> +# define atomic_inc_return(x) (__sync_add_and_fetch (&(x)->atomic, 1))
>> +# define atomic_dec_and_test(x) (__sync_add_and_fetch (&(x)->atomic, -1) == 0)
> The atomic_dec_and_test change seems like unrelated bugfix. Split it
> out perhaps ?
Not a bug fix, just swapping the order..
- atomic_fetch_and_add(-1) == 1
+ atomic_add_and_fetch(-1) == 0

> Introduction of atomic_inc_return could/should be a separate commit as well.



>>  # define atomic_add(x, v) ((void) __sync_add_and_fetch(&(x)->atomic, (v)))
>>  # define atomic_dec(x, v) ((void) __sync_sub_and_fetch(&(x)->atomic, (v)))
>>  # define atomic_cmpxchg(x, oldv, newv) __sync_val_compare_and_swap (&(x)->atomic, oldv, newv)
>> @@ -68,6 +69,7 @@ typedef struct {
>>  # define atomic_read(x) AO_load_full(&(x)->atomic)
>>  # define atomic_set(x, val) AO_store_full(&(x)->atomic, (val))
>>  # define atomic_inc(x) ((void) AO_fetch_and_add1_full(&(x)->atomic))
>> +# define atomic_inc_return(x) (AO_fetch_and_add1_full(&(x)->atomic) + 1)
>>  # define atomic_add(x, v) ((void) AO_fetch_and_add_full(&(x)->atomic, (v)))
>>  # define atomic_dec(x, v) ((void) AO_fetch_and_add_full(&(x)->atomic, -(v)))
>>  # define atomic_dec_and_test(x) (AO_fetch_and_sub1_full(&(x)->atomic) == 1)
>> @@ -91,6 +93,7 @@ typedef struct { LIBDRM_ATOMIC_TYPE atomic; } atomic_t;
>>  # define atomic_read(x) (int) ((x)->atomic)
>>  # define atomic_set(x, val) ((x)->atomic = (LIBDRM_ATOMIC_TYPE)(val))
>>  # define atomic_inc(x) (atomic_inc_uint (&(x)->atomic))
>> +# define atomic_inc_return (atomic_inc_uint_nv(&(x)->atomic))
>>  # define atomic_dec_and_test(x) (atomic_dec_uint_nv(&(x)->atomic) == 0)
>>  # define atomic_add(x, v) (atomic_add_int(&(x)->atomic, (v)))
>>  # define atomic_dec(x, v) (atomic_add_int(&(x)->atomic, -(v)))
>> @@ -112,3 +115,4 @@ static inline int atomic_add_unless(atomic_t *v, int add, int unless)
>>  }
>>
>>  #endif
>> +
> Extra white-space.
> 
> IMHO sending the series for dri-devel might be nice, for at least the
> xf86atomic.h changes.
Probably, not sure anyone will review it though, so I think just adding in a separate commit is fine.

> P.S. Bless you dude for going through the lovely experience to fix this.
Np. When I find some time I'll try nouveau in mesa next. :)

~Maarten
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