Fix peer access test synchronization issue

[rwgk]

This Cursor-generated change is expected to resolve failures in QA environments (nvbug 5821337).

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Problem

The test TestBufferPeerAccessAfterImport::test_main was failing with assertion errors indicating memory comparison failures. The root cause is most likely a synchronization issue when accessing peer memory.

When dev0 accesses peer memory from dev1, PatternGen.verify_buffer() only synchronizes dev0 (the accessing device) but not dev1 (the resident device). This can cause synchronization issues where dev0 reads peer memory before dev1 has completed all operations, leading to incorrect data being read.

Changes

• Added dev1.sync() call after IPC import (Test 1)
• Added dev1.sync() call after granting peer access (Test 3) before dev0 accesses peer memory

This follows CUDA best practices: when accessing peer memory, sync the resident device to ensure its operations are complete before the peer device reads the memory.

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[rwgk]

/ok to test

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[Andy-Jost]

This should not be needed. For one thing, IPC import APIs are synchronous; for another, verify_buffer in the next line synchronizes device 1

See lines 65 and 82 in

cuda-python/cuda_core/tests/helpers/buffers.py

Lines 61 to 66 in eec6988

	def __init__(self, device, size, stream=None):
	self.device = device
	self.size = size
	self.stream = stream if stream is not None else device.create_stream()
	self.sync_target = stream if stream is not None else device
	self.pattern_buffers = {}

and

cuda-python/cuda_core/tests/helpers/buffers.py

Lines 74 to 83 in eec6988

	def verify_buffer(self, buffer, seed=None, value=None):
	"""Verify the buffer contents against a sequential pattern."""
	assert buffer.size == self.size
	scratch_buffer = DummyUnifiedMemoryResource(self.device).allocate(self.size)
	ptr_test = self._ptr(scratch_buffer)
	pattern_buffer = self._get_pattern_buffer(seed, value)
	ptr_expected = self._ptr(pattern_buffer)
	scratch_buffer.copy_from(buffer, stream=self.stream)
	self.sync_target.sync()
	assert libc.memcmp(ptr_test, ptr_expected, self.size) == 0

[Andy-Jost]

I think this is also not needed. Peer accessibility APIs are synchronous.