Re: [og12] In 'libgomp/allocator.c:omp_realloc', route 'free' through 'MEMSPACE_FREE' (was: [PATCH] libgomp, OpenMP, nvptx: Low-latency memory allocator)

[Thomas Schwinge <thomas@codesourcery.com>]

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Hi!

On 2023-02-14T15:11:14+0000, Andrew Stubbs <ams@codesourcery.com> wrote:
> On 14/02/2023 12:54, Thomas Schwinge wrote:
>> 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.

No issues in testing.

>> Does that
>> look correct to you?
>
> That looks correct.

Thanks.  I've pushed to devel/omp/gcc-12 branch
commit 3a2c07395b0a565955a7b86f0eba866937e15989
"In 'libgomp/allocator.c:omp_realloc', route 'free' through 'MEMSPACE_FREE'",
see attached.

> The only remaining use of "free" should be the one
> referring to the allocator object itself (i.e. the destructor).

ACK.

>> 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.)
>
> The used_pool_size code comes from upstream, so if you want to go beyond
> the mechanical substitution of "free" then you're adding a new patch
> (rather than tweaking an old one). I'll leave that for others to comment on.

And I'll leave that for another day, and/or another person.  ;-)


Grüße
 Thomas


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From 3a2c07395b0a565955a7b86f0eba866937e15989 Mon Sep 17 00:00:00 2001
From: Thomas Schwinge <thomas@codesourcery.com>
Date: Tue, 14 Feb 2023 13:35:03 +0100
Subject: [PATCH] In 'libgomp/allocator.c:omp_realloc', route 'free' through
 'MEMSPACE_FREE'

... to not run into a SIGSEGV if a non-'malloc'-based allocation is 'free'd
here.

Fix-up for og12 commit c5d1d7651297a273321154a5fe1b01eba9dcf604
"libgomp, nvptx: low-latency memory allocator".

	libgomp/
	* allocator.c (omp_realloc): Route 'free' through 'MEMSPACE_FREE'.
---
 libgomp/ChangeLog.omp |  2 ++
 libgomp/allocator.c   | 12 +++++++++++-
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/libgomp/ChangeLog.omp b/libgomp/ChangeLog.omp
index 530f5c6acf6..819a5333907 100644
--- a/libgomp/ChangeLog.omp
+++ b/libgomp/ChangeLog.omp
@@ -1,5 +1,7 @@
 2023-02-16  Thomas Schwinge  <thomas@codesourcery.com>
 
+	* allocator.c (omp_realloc): Route 'free' through 'MEMSPACE_FREE'.
+
 	* config/linux/allocator.c (linux_memspace_alloc)
 	(linux_memspace_calloc): Clarify zero-initialization for pinned
 	memory.
diff --git a/libgomp/allocator.c b/libgomp/allocator.c
index 05b323d458e..ba9a4e17cc2 100644
--- a/libgomp/allocator.c
+++ b/libgomp/allocator.c
@@ -854,7 +854,17 @@ retry:
       gomp_mutex_unlock (&free_allocator_data->lock);
 #endif
     }
-  free (data->ptr);
+  {
+    omp_memspace_handle_t was_memspace __attribute__((unused))
+      = (free_allocator_data
+	 ? free_allocator_data->memspace
+	 : predefined_alloc_mapping[free_allocator]);
+    int was_pinned __attribute__((unused))
+      = (free_allocator_data
+	 ? free_allocator_data->pinned
+	 : free_allocator == ompx_pinned_mem_alloc);
+    MEMSPACE_FREE (was_memspace, data->ptr, data->size, was_pinned);
+  }
   return ret;
 
 fail:
-- 
2.25.1