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

[Rob Herring]

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.

Rob