Two threads both allocating 2MiB going into line 2091 and the check is false because freeMem_ is 3MiB.
Both threads will decrement the counter freeMem_ in line 2101 which results in an underflow
Case 2
Two threads where one is deallocating 2MiB and the other is allocating 5MiB and freeMem_ is 4MiB
The allocating thread (5MiB) is checking line 2091 and is going into the if body to line 2096
The second thread with the deallocation of 2MiB is exciting line 2088, freeMem_ is now 6MiB
The first thread is executing line 2098 which is setting freeMem_ to zero.
The result is that we lose 2MiB of memory we could potential allocate but due to the data race is not available anymore
Possible solution:
When memory is freed freeMem_ is stored in a register and atomic CAS is used to reset the variable freeMem_
line 2101 must be guarded by atomic Cas too to avoid that other threads reducing the value of freeMem_ in the same moment which results into a variant of Case 1
IMO the memory counting functions contain data races which lead to the possibility that the counter for free memory is underflowing.
https://github.com/ROCm-Developer-Tools/ROCclr/blob/90f1f61a9d6c28ffd2f844dc773e921444752e47/device/rocm/rocdevice.cpp#L2086-L2104
freeMem_is 3MiB.freeMem_in line 2101 which results in an underflowfreeMem_is 4MiBfreeMem_is now 6MiBfreeMem_to zero.Possible solution:
freeMem_is stored in a register and atomic CAS is used to reset the variablefreeMem_freeMem_in the same moment which results into a variant ofCase 1