Re: BPF Concurrency

Yonghong Song

On Sun, Jun 21, 2020 at 4:17 PM Kanthi P <Pavuluri.kanthi@...> wrote:

Thanks Andrii. __sync_fetch_and_add doesn't seem to work as expected, it is adding the increment, but it is returning the wrong value.
I am actually hitting the same issue mentioned here:,,,20,0,0,0::recentpostdate%2Fsticky,,,20,2,20,23670176

Can anyone suggest if it is fixed recently? I am on 4.15 kernel.
You cannot use the return value. A recent llvm should return an error
if you try to use it.

There is some preliminary work to have more atomic operations in the
BPF ISA. We could add a version of
fetch_and_add with proper return value. This may take some time as we
need to ensure kernel has proper support.


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