From: Michael Jeanson Date: Wed, 20 Jul 2022 18:49:56 +0000 (-0400) Subject: fix: num_possible_cpus() with hot-unplugged CPUs X-Git-Url: http://git.liburcu.org/?a=commitdiff_plain;h=66dbdc3448a77043d0fd59f47b17e77a8d59fddb;hp=66dbdc3448a77043d0fd59f47b17e77a8d59fddb;p=lttng-ust.git fix: num_possible_cpus() with hot-unplugged CPUs We rely on sysconf(_SC_NPROCESSORS_CONF) to get the maximum possible number of CPUs that can be attached to the system for the lifetime of an application. We use this value to allocate an array of per-CPU buffers that is indexed by the numerical id of the CPUs. As such we expect that the highest possible CPU id would be one less than the number returned by sysconf(_SC_NPROCESSORS_CONF) which is unfortunatly not always the case and can vary across libc implementations and versions. Glibc up to 2.35 will count the number of "cpuX" directories in "/sys/devices/system/cpu" which doesn't include CPUS that were hot-unplugged. This information is however provided by the kernel in "/sys/devices/system/cpu/possible" in the form of a mask listing all the CPUs that could possibly be hot-plugged in the system. This patch changes the implementation of num_possible_cpus() to first try parsing the possible CPU mask to extract the highest possible value and if this fails fallback to the previous behavior. Change-Id: I1a3cb1a446154ec443a391d6689cb7d4165726fd Signed-off-by: Michael Jeanson Signed-off-by: Mathieu Desnoyers ---