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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 <eddyz87@gmail.com>
Reviewed-by: Amery Hung <ameryhung@gmail.com>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20251029181828.231529-3-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
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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 <memxor@gmail.com>
Link: https://lore.kernel.org/r/20250927205304.199760-1-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
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Currently, the res_spin_lock test is too chatty as it constantly prints
the test_run results for each iteration in each thread, so in case
verbose output is requested or things go wrong, it will flood the logs
of CI and other systems with repeated messages that offer no valuable
insight. Reduce this by doing assertions when the condition actually
flips, and proceed to break out and exit the threads. We still assert
to mark the test as failed and print the expected and reported values.
Suggested-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20250403220841.66654-1-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
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Introduce selftests that trigger AA, ABBA deadlocks, and test the edge
case where the held locks table runs out of entries, since we then
fallback to the timeout as the final line of defense. Also exercise
verifier's AA detection where applicable.
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20250316040541.108729-26-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
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