Hi Andrew!

On 2022-01-13T11:13:51+0000, Andrew Stubbs <ams@codesourcery.com> wrote:
> Updated patch: this version fixes some missed cases of malloc in the
> realloc implementation.

Right, and as it seems I've run into another issue: a stray 'free'.

> --- a/libgomp/allocator.c
> +++ b/libgomp/allocator.c

Re 'omp_realloc':

> @@ -660,9 +709,10 @@ retry:
>        gomp_mutex_unlock (&allocator_data->lock);
>  #endif
>        if (prev_size)
> -     new_ptr = realloc (data->ptr, new_size);
> +     new_ptr = MEMSPACE_REALLOC (allocator_data->memspace, data->ptr,
> +                                 data->size, new_size);
>        else
> -     new_ptr = malloc (new_size);
> +     new_ptr = MEMSPACE_ALLOC (allocator_data->memspace, new_size);
>        if (new_ptr == NULL)
>       {
>  #ifdef HAVE_SYNC_BUILTINS
> @@ -690,7 +740,11 @@ retry:
>          && (free_allocator_data == NULL
>              || free_allocator_data->pool_size == ~(uintptr_t) 0))
>      {
> -      new_ptr = realloc (data->ptr, new_size);
> +      omp_memspace_handle_t memspace __attribute__((unused))
> +     = (allocator_data
> +        ? allocator_data->memspace
> +        : predefined_alloc_mapping[allocator]);
> +      new_ptr = MEMSPACE_REALLOC (memspace, data->ptr, data->size, new_size);
>        if (new_ptr == NULL)
>       goto fail;
>        ret = (char *) new_ptr + sizeof (struct omp_mem_header);
> @@ -701,7 +755,11 @@ retry:
>      }
>    else
>      {
> -      new_ptr = malloc (new_size);
> +      omp_memspace_handle_t memspace __attribute__((unused))
> +     = (allocator_data
> +        ? allocator_data->memspace
> +        : predefined_alloc_mapping[allocator]);
> +      new_ptr = MEMSPACE_ALLOC (memspace, new_size);
>        if (new_ptr == NULL)
>       goto fail;
>      }
> @@ -735,32 +793,35 @@ retry:
|    free (data->ptr);
>    return ret;

I run into a SIGSEGV if a non-'malloc'-based allocation is 'free'd here.

The attached
"In 'libgomp/allocator.c:omp_realloc', route 'free' through 'MEMSPACE_FREE'"
appears to resolve my issue, but not yet regression-tested.  Does that
look correct to you?

Or, instead of invoking 'MEMSPACE_FREE', should we scrap the
'used_pool_size' bookkeeping here, and just invoke 'omp_free' instead?

    --- libgomp/allocator.c
    +++ libgomp/allocator.c
    @@ -842,19 +842,7 @@ retry:
       if (old_size - old_alignment < size)
         size = old_size - old_alignment;
       memcpy (ret, ptr, size);
    -  if (__builtin_expect (free_allocator_data
    -                   && free_allocator_data->pool_size < ~(uintptr_t) 0, 0))
    -    {
    -#ifdef HAVE_SYNC_BUILTINS
    -      __atomic_add_fetch (&free_allocator_data->used_pool_size, -data->size,
    -                     MEMMODEL_RELAXED);
    -#else
    -      gomp_mutex_lock (&free_allocator_data->lock);
    -      free_allocator_data->used_pool_size -= data->size;
    -      gomp_mutex_unlock (&free_allocator_data->lock);
    -#endif
    -    }
    -  free (data->ptr);
    +  ialias_call (omp_free) (ptr, free_allocator);
       return ret;

(I've not yet analyzed whether that's completely equivalent.)


Note that this likewise applies to the current upstream submission:
<https://inbox.sourceware.org/gcc-patches/400092d8ce44340cece0e2e38f88edbad6400b03.1657188329.git.ams@codesourcery.com>
"libgomp, nvptx: low-latency memory allocator".


Grüße
 Thomas


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