feat(agnocast_kmod): replace do_exit kprobe with sched_process_exit tracepoint#1089
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k1832 wants to merge 2 commits intotier4:mainfrom
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feat(agnocast_kmod): replace do_exit kprobe with sched_process_exit tracepoint#1089k1832 wants to merge 2 commits intotier4:mainfrom
k1832 wants to merge 2 commits intotier4:mainfrom
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…it tracepoint Replace the kprobe on the internal `do_exit` symbol with the stable `sched_process_exit` tracepoint. This improves portability (do_exit is not a stable kernel API), reduces per-exit overhead (~20x less latency), and provides a formal unload safety guarantee via tracepoint_synchronize_unregister(). Use for_each_kernel_tracepoint() for dynamic lookup since the tracepoint symbol is not exported to modules. Signed-off-by: Keita Morisaki <keita.morisaki@tier4.jp>
Signed-off-by: Keita Morisaki <keita.morisaki@tier4.jp>
Koichi98
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Description
Replace the
do_exitkprobe with asched_process_exittracepoint for process exit detection.Why:
do_exitsched_process_exittracepointdo_exitis an internal symbol — no stability guarantee across kernel versionsint3breakpoint trap (x86) orBRK(arm64)nopwhen disabled,jmpwhen enabled)unregister_kprobe()— no explicit "all callbacks done" guaranteetracepoint_synchronize_unregister()— formal guarantee no callbacks in flightcurrent->pidtask_struct *directly — correct by construction#if LINUX_VERSION_CODEguards (6.2+__noreturn, 6.7+ inlining)The tracepoint symbol (
__tracepoint_sched_process_exit) is not exported to modules, so we use dynamic lookup viafor_each_kernel_tracepoint()+tracepoint_probe_register(), both of which areEXPORT_SYMBOL_GPLand compatible with the module'sMODULE_LICENSE("Dual BSD/GPL").Behavioral equivalence: The kprobe handler and tracepoint callback both call
enqueue_exit_pid(pid). The cleanup logic (process_exit_cleanup,exit_worker_thread, ring buffer) is completely unchanged.task->pidis valid at both hook points — the PID is not freed untilexit_notify()→release_task(), which runs after the tracepoint.Benchmark (50000 ×
/bin/trueon same machine):No measurable throughput difference. This is expected — the ~1 us per-call saving is invisible in a test dominated by fork+exec+exit cost (~3.8 ms per iteration). The real value is portability (stable API), unload safety (
tracepoint_synchronize_unregister), and eliminating preemption-disabled windows.Related links
How was this PR tested?
bash scripts/test/e2e_test_1to1(required)bash scripts/test/e2e_test_2to2(required)KUnit tests do not need changes — they call
enqueue_exit_pid()/process_exit_cleanup()directly and do not exercise the hook mechanism.Notes for reviewers
for_each_kernel_tracepoint()is used for dynamic tracepoint lookup because the static tracepoint symbol is not exported to modules. This is a standard pattern used by other out-of-tree modules.tracepoint_synchronize_unregister()is called during module exit to guarantee no callbacks are in flight before the module is unloaded.