Fix UB in atomics with automatic storage #2586
Open
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Co-authored-by: Georgy Evtushenko <[email protected]> Co-authored-by: gonzalobg <[email protected]>
miscco
reviewed
Oct 16, 2024
| // uses inline PTX to bypass __isLocal. | ||
| _LIBCUDACXX_BEGIN_NAMESPACE_STD | ||
|
|
||
| _CCCL_DEVICE inline bool __cuda_is_local(const void* __ptr) |
There was a problem hiding this comment.
Should we prefix those with __cccl?
| { | ||
| return false; | ||
| } | ||
| if (0 == __atomic_memcmp((const void*) __ptr, (const void*) __expected, sizeof(_Type))) |
There was a problem hiding this comment.
Please swap
Suggested change
| if (0 == __atomic_memcmp((const void*) __ptr, (const void*) __expected, sizeof(_Type))) | |
| if (__atomic_memcmp((const void*) __ptr, (const void*) __expected, sizeof(_Type)) == 0) |
| } | ||
| memcpy((void*) __ptr, (void const*) &__val, sizeof(_Type)); | ||
| return true; | ||
| #else |
Comment on lines
+88
to
+103
| template <class _Type> | ||
| _CCCL_DEVICE bool __cuda_load_weak_if_local(const volatile _Type* __ptr, _Type* __ret) | ||
| { | ||
| #if defined(_LIBCUDACXX_ATOMIC_UNSAFE_AUTOMATIC_STORAGE) | ||
| if (!__cuda_is_local((const void*) __ptr)) | ||
| { | ||
| return false; | ||
| } | ||
| memcpy((void*) __ret, (void const*) __ptr, sizeof(_Type)); | ||
| // Required to workaround a compiler bug, see nvbug/4064730 | ||
| __nanosleep(0); | ||
| return true; | ||
| #else | ||
| return false; | ||
| #endif | ||
| } |
There was a problem hiding this comment.
Question: This is only needing the size of _Type
Could we pass in a void* and either template this on size_t or pass it as an argument?
Applies below
gonzalobg
reviewed
Oct 17, 2024
| _CCCL_DEVICE bool | ||
| __cuda_compare_exchange_weak_if_local(volatile _Type* __ptr, _Type* __expected, const _Type* __desired, bool* __success) | ||
| { | ||
| if (!__cuda_is_local((const void*) __ptr)) |
There was a problem hiding this comment.
We are missing the #if defined(_LIBCUDACXX_ATOMIC_UNSAFE_AUTOMATIC_STORAGE).
I'd expect that we'd want it here for the same reason we want it in the other ops.
And ditto for the ops below.
(If we don't need it, I don't remember why)
gonzalobg
reviewed
Oct 17, 2024
| // Enable bypassing automatic storage checks in atomics when using CTK 12.2 and below and if NDEBUG is defined. | ||
| # if defined(_CCCL_CUDACC_BELOW_12_2) && !defined(NDEBUG) | ||
| # define _LIBCUDACXX_ATOMIC_UNSAFE_AUTOMATIC_STORAGE | ||
| # endif // _CCCL_CUDACC_BELOW_12_2 |
There was a problem hiding this comment.
@gevtushenko fyi (I remember you had feedback about this)
ericniebler
reviewed
Oct 24, 2024
| @@ -154,6 +154,8 @@ static inline _CCCL_DEVICE bool __atomic_compare_exchange_cuda(_Type* __ptr, _Ty | |||
| __proxy_t* __ptr_proxy = reinterpret_cast<__proxy_t*>(__ptr); | |||
| __proxy_t* __exp_proxy = reinterpret_cast<__proxy_t*>(__exp); | |||
| __proxy_t* __des_proxy = reinterpret_cast<__proxy_t*>(&__des); | |||
| bool __res = false; | |||
| if (__cuda_compare_exchange_weak_if_local(__ptr_proxy, __exp_proxy, __des_proxy, &__res)) {{return __res;}} | |||
There was a problem hiding this comment.
probably a n00b question, but why the double braces {{}}?
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Description
Closes #2585
See #478 for more details.
This fixes UB when using automatic storage with atomics (which has little or no use-case)
Example of users encountering wrong values in automatic storage: https://stackoverflow.com/questions/75640847/what-exactly-does-cudaatomic-does
Checklist