[Mesa-dev] [PATCH] vc4: add hash table look-up for exported dmabufs

[Eric Anholt]

Rob Herring <robh at kernel.org> writes:

> It is necessary to reuse existing BOs when dmabufs are imported. There
> are 2 cases that need to be handled. dmabufs can be created/exported and
> imported by the same process and can be imported multiple times.
> Copying other drivers, add a hash table to track exported BOs so the
> BOs get reused.
>
> Cc: Eric Anholt <eric at anholt.net>
> Signed-off-by: Rob Herring <robh at kernel.org>
> ---
> With this and the fd hashing to get a single screen, the flickery screen 
> is gone and Android is somewhat working. Several apps though hang, don't 
> render, and then exit. I also see CMA allocation errors, but not 
> correlating to the app problems.
>
> Also, flink names need similar hash table look-up as well. Maybe that's 
> a don't care for vc4? In any case, I don't have the setup to test that.
>
> Rob
>
>  src/gallium/drivers/vc4/vc4_bufmgr.c | 20 +++++++++++++++++++-
>  src/gallium/drivers/vc4/vc4_bufmgr.h | 12 +++++++++++-
>  src/gallium/drivers/vc4/vc4_screen.c | 15 +++++++++++++++
>  src/gallium/drivers/vc4/vc4_screen.h |  3 +++
>  4 files changed, 48 insertions(+), 2 deletions(-)
>
> diff --git a/src/gallium/drivers/vc4/vc4_bufmgr.c b/src/gallium/drivers/vc4/vc4_bufmgr.c
> index 21e3bde..d91157b 100644
> --- a/src/gallium/drivers/vc4/vc4_bufmgr.c
> +++ b/src/gallium/drivers/vc4/vc4_bufmgr.c
> @@ -28,6 +28,7 @@
>  #include <xf86drm.h>
>  #include <xf86drmMode.h>
>  
> +#include "util/u_hash_table.h"
>  #include "util/u_memory.h"
>  #include "util/ralloc.h"
>  
> @@ -329,10 +330,19 @@ vc4_bo_open_handle(struct vc4_screen *screen,
>                     uint32_t winsys_stride,
>                     uint32_t handle, uint32_t size)
>  {
> -        struct vc4_bo *bo = CALLOC_STRUCT(vc4_bo);
> +        struct vc4_bo *bo;
>  
>          assert(size);
>  
> +        pipe_mutex_lock(screen->bo_handles_mutex);
> +
> +        bo = util_hash_table_get(screen->bo_handles, (void*)(uintptr_t)handle);
> +        if (bo) {
> +                pipe_reference(NULL, &bo->reference);
> +                goto done;
> +        }
> +
> +        bo = CALLOC_STRUCT(vc4_bo);
>          pipe_reference_init(&bo->reference, 1);
>          bo->screen = screen;
>          bo->handle = handle;
> @@ -347,6 +357,10 @@ vc4_bo_open_handle(struct vc4_screen *screen,
>          bo->map = malloc(bo->size);
>  #endif
>  
> +        util_hash_table_set(screen->bo_handles, (void *)(uintptr_t)handle, bo);
> +
> +done:
> +        pipe_mutex_unlock(screen->bo_handles_mutex);
>          return bo;
>  }
>  
> @@ -401,6 +415,10 @@ vc4_bo_get_dmabuf(struct vc4_bo *bo)
>          }
>          bo->private = false;
>  
> +        pipe_mutex_lock(bo->screen->bo_handles_mutex);
> +        util_hash_table_set(bo->screen->bo_handles, (void *)(uintptr_t)bo->handle, bo);
> +        pipe_mutex_unlock(bo->screen->bo_handles_mutex);
> +
>          return fd;
>  }
>  
> diff --git a/src/gallium/drivers/vc4/vc4_bufmgr.h b/src/gallium/drivers/vc4/vc4_bufmgr.h
> index b77506e..0896b30 100644
> --- a/src/gallium/drivers/vc4/vc4_bufmgr.h
> +++ b/src/gallium/drivers/vc4/vc4_bufmgr.h
> @@ -25,6 +25,7 @@
>  #define VC4_BUFMGR_H
>  
>  #include <stdint.h>
> +#include "util/u_hash_table.h"
>  #include "util/u_inlines.h"
>  #include "vc4_qir.h"
>  
> @@ -87,11 +88,20 @@ vc4_bo_reference(struct vc4_bo *bo)
>  static inline void
>  vc4_bo_unreference(struct vc4_bo **bo)
>  {
> +        struct vc4_screen *screen;
>          if (!*bo)
>                  return;
>  
> -        if (pipe_reference(&(*bo)->reference, NULL))
> +        screen = (*bo)->screen;
> +        pipe_mutex_lock(screen->bo_handles_mutex);
> +
> +        if (pipe_reference(&(*bo)->reference, NULL)) {
>                  vc4_bo_last_unreference(*bo);
> +                util_hash_table_remove(screen->bo_handles,
> +                                       (void *)(uintptr_t)(*bo)->handle);

I think you're use-after-freeing bo here.  Just stick it before
last_unreference()?

> +        }
> +
> +        pipe_mutex_unlock(screen->bo_handles_mutex);
>          *bo = NULL;
>  }

Taking a mutex on every unref sucks -- it's a *really* hot path, and it
kind of defeats the point of doing these pipe_reference atomics.  We
should be able to skip the mutex in the bo->private case, since any
flinked/dmabuf BO will be !private.  Think you could give that a shot?

Thanks for debugging!  Note, I'm still on vacation, so I'll be slow at
replying.
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