lwn.git/tools/testing/selftests/bpf/test_kmods/bpf_test_rqspinlock.c, branch master

selftests/bpf: Add success stats to rqspinlock stress test

2025-11-29T17:35:36+00:00

Add stats to observe the success and failure rate of lock acquisition attempts in various contexts. Signed-off-by: Kumar Kartikeya Dwivedi Link: https://lore.kernel.org/r/20251128232802.1031906-7-memxor@gmail.com Signed-off-by: Alexei Starovoitov

selftests/bpf: Make CS length configurable for rqspinlock stress test

2025-11-25T23:30:14+00:00

Allow users to configure the critical section delay for both task/normal and NMI contexts, and set to 20ms and 10ms as before by default. Signed-off-by: Kumar Kartikeya Dwivedi Link: https://lore.kernel.org/r/20251125020749.2421610-4-memxor@gmail.com Signed-off-by: Alexei Starovoitov

selftests/bpf: Add lock wait time stats to rqspinlock stress test

2025-11-25T23:30:14+00:00

Add statistics per-CPU broken down by context and various timing windows for the time taken to acquire an rqspinlock. Cases where all acquisitions fit into the 10ms window are skipped from printing, otherwise the full breakdown is displayed when printing the summary. This allows capturing precisely the number of times outlier attempts happened for a given lock in a given context. A critical detail is that time is captured regardless of success or failure, which is important to capture events for failed but long waiting timeout attempts. Output: [ 64.279459] rqspinlock acquisition latency histogram (ms): [ 64.279472] cpu1: total 528426 (normal 526559, nmi 1867) [ 64.279477] 0-1ms: total 524697 (normal 524697, nmi 0) [ 64.279480] 2-2ms: total 3652 (normal 1811, nmi 1841) [ 64.279482] 3-3ms: total 66 (normal 47, nmi 19) [ 64.279485] 4-4ms: total 2 (normal 1, nmi 1) [ 64.279487] 5-5ms: total 1 (normal 1, nmi 0) [ 64.279489] 6-6ms: total 1 (normal 0, nmi 1) [ 64.279490] 101-150ms: total 1 (normal 0, nmi 1) [ 64.279492] >= 251ms: total 6 (normal 2, nmi 4) ... Signed-off-by: Kumar Kartikeya Dwivedi Link: https://lore.kernel.org/r/20251125020749.2421610-3-memxor@gmail.com Signed-off-by: Alexei Starovoitov

selftests/bpf: Relax CPU requirements for rqspinlock stress test

2025-11-25T23:30:13+00:00

Only require 2 CPUs for AA, 3 for ABBA, 4 for ABBCCA, which is calculated nicely by adding to the mode enum. Enables running single CPU AA tests. Signed-off-by: Kumar Kartikeya Dwivedi Link: https://lore.kernel.org/r/20251125020749.2421610-2-memxor@gmail.com Signed-off-by: Alexei Starovoitov

selftests/bpf: Add ABBCCA case for rqspinlock stress test

2025-10-30T01:17:56+00:00

Introduce a new mode for the rqspinlock stress test that exercises a deadlock that won't be detected by the AA and ABBA checks, such that we always reliably trigger the timeout fallback. We need 4 CPUs for this particular case, as CPU 0 is untouched, and three participant CPUs for triggering the ABBCCA case. Refactor the lock acquisition paths in the module to better reflect the three modes and choose the right lock depending on the context. Also drop ABBA case from running by default as part of test progs, since the stress test can consume a significant amount of time. Acked-by: Eduard Zingerman Reviewed-by: Amery Hung Signed-off-by: Kumar Kartikeya Dwivedi Link: https://lore.kernel.org/r/20251029181828.231529-3-memxor@gmail.com Signed-off-by: Alexei Starovoitov

selftests/bpf: Add stress test for rqspinlock in NMI

2025-09-28T10:18:40+00:00

Introduce a kernel module that will exercise lock acquisition in the NMI path, and bias toward creating contention such that NMI waiters end up being non-head waiters. Prior to the rqspinlock fix made in the commit 0d80e7f951be ("rqspinlock: Choose trylock fallback for NMI waiters"), it was possible for the queueing path of non-head waiters to get stuck in NMI, which this stress test reproduces fairly easily with just 3 CPUs. Both AA and ABBA flavors are supported, and it will serve as a test case for future fixes that address this corner case. More information about the problem in question is available in the commit cited above. When the fix is reverted, this stress test will lock up the system. To enable this test automatically through the test_progs infrastructure, add a load_module_params API to exercise both AA and ABBA cases when running the test. Note that the test runs for at most 5 seconds, and becomes a noop after that, in order to allow the system to make forward progress. In addition, CPU 0 is always kept untouched by the created threads and NMIs. The test will automatically scale to the number of available online CPUs. Note that at least 3 CPUs are necessary to run this test, hence skip the selftest in case the environment has less than 3 CPUs available. Signed-off-by: Kumar Kartikeya Dwivedi Link: https://lore.kernel.org/r/20250927205304.199760-1-memxor@gmail.com Signed-off-by: Alexei Starovoitov