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
0d80e7f951 ("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>
The selftests build four kernel modules which use copy-pasted Makefile
targets. This is a bit messy, and doesn't scale so well when we add more
modules, so let's consolidate these rules into a single rule generated
for each module name, and move the module sources into a single
directory.
To avoid parallel builds of the different modules stepping on each
other's toes during the 'modpost' phase of the Kbuild 'make modules',
the module files should really be a grouped target. However, make only
added explicit support for grouped targets in version 4.3, which is
newer than the minimum version supported by the kernel. However, make
implicitly treats pattern matching rules with multiple targets as a
grouped target, so we can work around this by turning the rule into a
pattern matching target. We do this by replacing '.ko' with '%ko' in the
targets with subst().
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Viktor Malik <vmalik@redhat.com>
Link: https://lore.kernel.org/bpf/20241204-bpf-selftests-mod-compile-v5-1-b96231134a49@redhat.com
