Pass external callchain entry to get_perf_callchain #6317
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November 10, 2025 18:58
From BPF stack map, we want to ensure that the callchain buffer will not be overwritten by other preemptive tasks. Peter suggested provide more flexible stack-sampling APIs, which can be used in BPF, and we can still use the perf callchain entry with the help of these APIs. The next patch will modify the BPF part. In the future, these APIs will also make it convenient for us to add stack-sampling kfuncs in the eBPF subsystem, just as Andrii and Alexei discussed earlier. Signed-off-by: Peter Zijlstra <[email protected]> Signed-off-by: Tao Chen <[email protected]>
From BPF side, preemption usually is enabled. Yonghong said, it is possible that both tasks (at process level) may reach right before "recursion[rctx]++;". In such cases, both tasks will be able to get buffer and this is not right. Signed-off-by: Yonghong Song <[email protected]> Signed-off-by: Tao Chen <[email protected]>
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As Alexei noted, get_perf_callchain() return values may be reused if a task is preempted after the BPF program enters migrate disable mode. The perf_callchain_entres has a small stack of entries, and we can reuse it as follows: 1. get the perf callchain entry 2. BPF use... 3. put the perf callchain entry Signed-off-by: Tao Chen <[email protected]>
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Pull request for series with
subject: Pass external callchain entry to get_perf_callchain
version: 5
url: https://patchwork.kernel.org/project/netdevbpf/list/?series=1021316