Am 07.08.2017 um 13:44 schrieb Monk Liu:
> From: Monk Liu <monk.liu at amd.com>
>
> there is race issue between two threads on amdgpu_bo_free
> and amdgpu_bo_import, this patch tend to fix it by moving
> the pthread_mutex_lock out of bo_internal and cover
> the update_reference function.
>
> besides the mutex_unlock in bo_import should also cover
> bo refcount increasement.
Nice catch, but the solution is to heavy.
>
> Change-Id: I8ec5a2879dda0e6468864fc64e6b46059482998b
> Find-by: Deng hui <hui.deng at amd.com>
> Signed-off-by: Monk Liu <monk.liu at amd.com>
> ---
> amdgpu/amdgpu_bo.c | 13 +++++--------
> amdgpu/amdgpu_internal.h | 17 +++++++++++++++--
> 2 files changed, 20 insertions(+), 10 deletions(-)
>
> diff --git a/amdgpu/amdgpu_bo.c b/amdgpu/amdgpu_bo.c
> index ec99488..10a3efe 100644
> --- a/amdgpu/amdgpu_bo.c
> +++ b/amdgpu/amdgpu_bo.c
> @@ -52,27 +52,22 @@ static void amdgpu_close_kms_handle(amdgpu_device_handle dev,
> drmIoctl(dev->fd, DRM_IOCTL_GEM_CLOSE, &args);
> }
>
> -void amdgpu_bo_free_internal(amdgpu_bo_handle bo)
> +drm_private void amdgpu_bo_free_internal(amdgpu_bo_handle bo)
> {
> /* Remove the buffer from the hash tables. */
> - pthread_mutex_lock(&bo->dev->bo_table_mutex);
> util_hash_table_remove(bo->dev->bo_handles,
> (void*)(uintptr_t)bo->handle);
> if (bo->flink_name) {
> util_hash_table_remove(bo->dev->bo_flink_names,
> (void*)(uintptr_t)bo->flink_name);
> }
> - pthread_mutex_unlock(&bo->dev->bo_table_mutex);
>
> /* Release CPU access. */
> if (bo->cpu_map_count > 0) {
> bo->cpu_map_count = 1;
> amdgpu_bo_cpu_unmap(bo);
> }
> -
> amdgpu_close_kms_handle(bo->dev, bo->handle);
> - pthread_mutex_destroy(&bo->cpu_access_mutex);
> - free(bo);
> }
>
> int amdgpu_bo_alloc(amdgpu_device_handle dev,
> @@ -297,6 +292,7 @@ int amdgpu_bo_import(amdgpu_device_handle dev,
> /* Get a KMS handle. */
> r = drmPrimeFDToHandle(dev->fd, shared_handle, &handle);
> if (r) {
> + pthread_mutex_unlock(&dev->bo_table_mutex);
> return r;
> }
>
> @@ -339,10 +335,9 @@ int amdgpu_bo_import(amdgpu_device_handle dev,
> }
>
> if (bo) {
> - pthread_mutex_unlock(&dev->bo_table_mutex);
> -
> /* The buffer already exists, just bump the refcount. */
> atomic_inc(&bo->refcount);
> + pthread_mutex_unlock(&dev->bo_table_mutex);
Actually the problem is only here, that one needs to use
atomic_inc_unless() before the mutex is dropped and return only if we
could successfully acquire a reference to the BO.
All other changes are unnecessary.
>
> output->buf_handle = bo;
> output->alloc_size = bo->alloc_size;
> @@ -466,6 +461,8 @@ int amdgpu_bo_cpu_map(amdgpu_bo_handle bo, void **cpu)
> bo->cpu_map_count = 1;
> pthread_mutex_unlock(&bo->cpu_access_mutex);
>
> + amdgpu_add_handle_to_table(bo);
Well that is clearly a NAK. IIRC we discussed that before and came to
the conclusion that it isn't a good idea.
But it looks unrelated to the other changes, so why do you want to add
it now?
Regards,
Christian.
> +
> *cpu = ptr;
> return 0;
> }
> diff --git a/amdgpu/amdgpu_internal.h b/amdgpu/amdgpu_internal.h
> index 0508131..e1a6559 100644
> --- a/amdgpu/amdgpu_internal.h
> +++ b/amdgpu/amdgpu_internal.h
> @@ -30,6 +30,9 @@
>
> #include <assert.h>
> #include <pthread.h>
> +#include <stdlib.h>
> +
> +#include "libdrm_macros.h"
> #include "xf86atomic.h"
> #include "amdgpu.h"
> #include "util_double_list.h"
> @@ -193,8 +196,18 @@ static inline bool update_references(atomic_t *dst, atomic_t *src)
> static inline void amdgpu_bo_reference(struct amdgpu_bo **dst,
> struct amdgpu_bo *src)
> {
> - if (update_references(&(*dst)->refcount, &src->refcount))
> - amdgpu_bo_free_internal(*dst);
> + struct amdgpu_bo* bo = *dst;
> + assert(bo!=NULL);
> +
> + pthread_mutex_lock(&bo->dev->bo_table_mutex);
> +
> + if (update_references(&bo->refcount, src?&src->refcount:NULL)) {
> + amdgpu_bo_free_internal(bo);
> + pthread_mutex_destroy(&bo->cpu_access_mutex);
> + pthread_mutex_unlock(&bo->dev->bo_table_mutex);
> + free(bo);
> + } else
> + pthread_mutex_unlock(&bo->dev->bo_table_mutex);
> *dst = src;
> }
>
