rtla: Abort on nr_cpus mismatch with tracer

In rare situations, sysfs might report a different number of CPUs than
the kernel sees, for example, when /sys is not real sysfs.

In tracefs mode, RTLA will discard any samples that are reported on CPUs
higher than the maximum in sysfs. However, in BPF mode, the incorrectly
sized BPF_MAP_LOOKUP_ELEM syscall on percpu maps will cause a buffer
overflow.

To cover for this corner case, write "all" to osnoise/cpus, and read
back the real kernel-side list of all possible cpus. If it doesn't match
RTLA's nr_cpus (read from sysfs), abort with an error.

Assisted-by: Claude:claude-opus-4-6
Link: https://lore.kernel.org/r/20260814135511.2207190-4-tglozar@redhat.com
Signed-off-by: Tomas Glozar <tglozar@redhat.com>

0 files changed, 0 insertions, 0 deletions