The user triggers the creation of a pseudo-locked region when writing the requested schemata to the schemata resctrl file. The pseudo-locking of a region is required to be done on a CPU that is associated with the cache on which the pseudo-locked region will reside. In order to run the locking code on a specific CPU the needed CPU has to be selected and ensured to remain online during the entire locking sequence.

At this time the cpu_hotplug_lock is not taken during the pseudo-lock region creation and it is thus possible for a CPU to be selected to run the pseudo-locking code and then that CPU to go offline before the thread is able to run on it.

Fix this by ensuring that the cpu_hotplug_lock is taken while the CPU on which code has to run needs to be controlled. Since the cpu_hotplug_lock is always taken before rdtgroup_mutex the lock order is maintained.

Fixes: e0bdfe8e36f3 ("x86/intel_rdt: Support creation/removal of pseudo-locked region") Signed-off-by: Reinette Chatre reinette.chatre@intel.com Cc: stable@vger.kernel.org --- arch/x86/kernel/cpu/resctrl/ctrlmondata.c | 4 ++++ 1 file changed, 4 insertions(+)

diff --git a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c index 03ee13235a45..6f7adb3be01e 100644 --- a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c +++ b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c @@ -23,6 +23,7 @@

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

+#include <linux/cpu.h> #include <linux/kernfs.h> #include <linux/seq_file.h> #include <linux/slab.h> @@ -381,9 +382,11 @@ ssize_t rdtgroup_schemata_write(struct kernfs_open_file *of, return -EINVAL; buf[nbytes - 1] = '\0';

+ cpus_read_lock(); rdtgrp = rdtgroup_kn_lock_live(of->kn); if (!rdtgrp) { rdtgroup_kn_unlock(of->kn); + cpus_read_unlock(); return -ENOENT; } rdt_last_cmd_clear(); @@ -438,6 +441,7 @@ ssize_t rdtgroup_schemata_write(struct kernfs_open_file *of,

out: rdtgroup_kn_unlock(of->kn); + cpus_read_unlock(); return ret ?: nbytes; }