[Mesa-dev] [PATCH v4 03/11] gallium: add common pipe_screen reference counting functions

[Emil Velikov]

On 22 July 2016 at 19:01, Rob Herring <robh at kernel.org> wrote:
> On Fri, Jul 22, 2016 at 11:46 AM, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
>> On Fri, Jul 22, 2016 at 12:22 PM, Rob Herring <robh at kernel.org> wrote:
>>> In order to prevent multiple pipe_screens being created in the same
>>> process, lookup of the DRM FD and reference counting of the pipe_screen
>>> are needed. Several implementations of this exist in various gallium
>>> drivers/winsys already. This creates a common version which is opt-in
>>> for winsys implementations.
>>>
>>> Signed-off-by: Rob Herring <robh at kernel.org>
>>> ---
>>>  src/gallium/auxiliary/Makefile.sources |   2 +
>>>  src/gallium/auxiliary/util/u_screen.c  | 114 +++++++++++++++++++++++++++++++++
>>>  src/gallium/auxiliary/util/u_screen.h  |  32 +++++++++
>>>  src/gallium/include/pipe/p_screen.h    |   3 +
>>>  4 files changed, 151 insertions(+)
>>>  create mode 100644 src/gallium/auxiliary/util/u_screen.c
>>>  create mode 100644 src/gallium/auxiliary/util/u_screen.h
>>>
>>> diff --git a/src/gallium/auxiliary/Makefile.sources b/src/gallium/auxiliary/Makefile.sources
>>> index e0311bf..197ed36 100644
>>> --- a/src/gallium/auxiliary/Makefile.sources
>>> +++ b/src/gallium/auxiliary/Makefile.sources
>>> @@ -284,6 +284,8 @@ C_SOURCES := \
>>>         util/u_ringbuffer.h \
>>>         util/u_sampler.c \
>>>         util/u_sampler.h \
>>> +       util/u_screen.c \
>>> +       util/u_screen.h \
>>>         util/u_simple_shaders.c \
>>>         util/u_simple_shaders.h \
>>>         util/u_slab.c \
>>> diff --git a/src/gallium/auxiliary/util/u_screen.c b/src/gallium/auxiliary/util/u_screen.c
>>> new file mode 100644
>>> index 0000000..47bad11
>>> --- /dev/null
>>> +++ b/src/gallium/auxiliary/util/u_screen.c
>>> @@ -0,0 +1,114 @@
>>> +/*
>>> + * Copyright 2016 Linaro, Ltd., Rob Herring <robh at kernel.org>
>>> + *
>>> + * 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, sub license, 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 (including the
>>> + * next paragraph) 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 NON-INFRINGEMENT.
>>> + * IN NO EVENT SHALL VMWARE AND/OR ITS SUPPLIERS 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.
>>> + */
>>> +
>>> +/**
>>> + * Functions for managing pipe_screen's
>>> + */
>>> +
>>> +#include <sys/stat.h>
>>> +
>>> +#include "os/os_thread.h"
>>> +
>>> +#include "pipe/p_screen.h"
>>> +#include "util/u_hash_table.h"
>>> +#include "util/u_inlines.h"
>>> +#include "util/u_pointer.h"
>>> +#include "util/u_screen.h"
>>> +
>>> +static struct util_hash_table *fd_tab = NULL;
>>> +pipe_static_mutex(fd_tab_mutex);
>>> +
>>> +static unsigned hash_fd(void *key)
>>> +{
>>> +   int fd = pointer_to_intptr(key);
>>> +   struct stat stat;
>>> +   fstat(fd, &stat);
>>> +
>>> +   return stat.st_dev ^ stat.st_ino ^ stat.st_rdev;
>>> +}
>>> +
>>> +static int compare_fd(void *key1, void *key2)
>>> +{
>>> +   int fd1 = pointer_to_intptr(key1);
>>> +   int fd2 = pointer_to_intptr(key2);
>>> +   struct stat stat1, stat2;
>>> +   fstat(fd1, &stat1);
>>> +   fstat(fd2, &stat2);
>>> +
>>> +   return stat1.st_dev != stat2.st_dev ||
>>> +         stat1.st_ino != stat2.st_ino ||
>>> +         stat1.st_rdev != stat2.st_rdev;
>>> +}
>>> +
>>> +struct pipe_screen *
>>> +pipe_screen_reference(int fd)
>>> +{
>>> +   struct pipe_screen *pscreen;
>>> +
>>> +   if (!fd_tab) {
>>> +      fd_tab = util_hash_table_create(hash_fd, compare_fd);
>>
>> Do you need to grab the fd_tab_mutex around this? What if two
>> pipe_screen_reference() calls race to be the first ones?
>
> No, but only because the loader_mutex serializes things. That's not
> obvious though so putting fd_tab_mutex around it would make this
> function more robust.
>
>>> +      return NULL;
>>> +   }
>>> +
>>> +   pipe_mutex_lock(fd_tab_mutex);
>>> +   pscreen = util_hash_table_get(fd_tab, intptr_to_pointer(fd));
>>> +   if (pscreen)
>>> +      pipe_reference(NULL, &pscreen->reference);
>>> +   pipe_mutex_unlock(fd_tab_mutex);
>>> +
>>> +   return pscreen;
>>> +}
>>> +
>>> +boolean
>>> +pipe_screen_unreference(struct pipe_screen *pscreen)
>>> +{
>>> +   boolean destroy;
>>> +
>>> +   if (!pscreen)
>>> +      return FALSE;
>>> +
>>> +   /* Work-around until all pipe_screens have ref counting */
>>> +   if (!pipe_is_referenced(&pscreen->reference)) {
>>> +      pscreen->destroy(pscreen);
>>> +      return TRUE;
>>> +   }
>>> +
>>> +   pipe_mutex_lock(fd_tab_mutex);
>>> +   destroy = pipe_reference(&pscreen->reference, NULL);
>>> +   if (destroy) {
>>> +      pscreen->destroy(pscreen);
>>> +      util_hash_table_remove(fd_tab, intptr_to_pointer(pscreen->fd));
>>> +      close(pscreen->fd);
>>
>> It seems a little odd that you're closing a fd that you didn't
>> open/dup in this library. It's a bit of asymmetry in the calling
>> convention.
>
> Yes, the asymmetry in general compared to the RFC bugs me a bit too.
> The flip side is duplicating the close in all the destroy() functions
> seems pointless.
>
> Also, I just noticed I have a use after free problem here. The
> destroy() call needs to be last.
>
Haven't checked if all the drivers will need the close() and/or how
likely are things to say boom, so let's keep that as separate patch ?

Thanks
Emil