A tool to verify the BPF memory model #5587
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As BPF doesn't include any barrier instructions, smp_mb() is implemented by doing a dummy value returning atomic operation. Such an operation acts a full barrier as enforced by LKMM and also by the work in progress BPF memory model. If the returned value is not used, clang[1] can optimize the value returning atomic instruction in to a normal atomic instruction which provides no ordering guarantees. Mark the variable as volatile so the above optimization is never performed and smp_mb() works as expected. [1] https://godbolt.org/z/qzze7bG6z Fixes: 88d706b ("selftests/bpf: Introduce arena spin lock") Signed-off-by: Puranjay Mohan <[email protected]>
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Pull request for series with
subject: A tool to verify the BPF memory model
version: 1
url: https://patchwork.kernel.org/project/netdevbpf/list/?series=981178