From b8eb5fd5bdb4c03758b056c70e5e1d962ca89757 Mon Sep 17 00:00:00 2001 From: Waiman Long Date: Mon, 5 Oct 2026 06:43:10 -0400 Subject: [PATCH] cgroup/cpuset: Call is_in_v2_mode() after acquiring cpuset_mutex in cpuset_handle_hotplug() It is reported by sashiko that calling is_in_v2_mode() outside of cpuset_mutex critical section in cpuset_handle_hotplug() can introduce a TOCTOU race where cgroup hierarchy may have changed from v1 to v2 or vice versa after is_in_v2_mode() is called leading to erroneously skip the allocation of tmpmasks or incorrectly modify cpus_allowed masks, resulting in cpuset state corruption. Fix that by calling is_in_v2_mode() after acquiring the cpuset_mutex. Fixes: b8d1b8ee93df ("cpuset: Allow v2 behavior in v1 cgroup") Signed-off-by: Waiman Long Signed-off-by: Tejun Heo --- kernel/cgroup/cpuset.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c index d2ec7b128960..b61bc3ed1037 100644 --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -4062,15 +4062,16 @@ static void cpuset_handle_hotplug(void) static cpumask_t new_cpus; static nodemask_t new_mems; bool cpus_updated, mems_updated; - bool on_dfl = is_in_v2_mode(); + bool on_dfl; struct tmpmasks tmp, *ptmp = NULL; - if (on_dfl && !alloc_tmpmasks(&tmp)) - ptmp = &tmp; - lockdep_assert_cpus_held(); mutex_lock(&cpuset_mutex); + on_dfl = is_in_v2_mode(); + if (on_dfl && !alloc_tmpmasks(&tmp)) + ptmp = &tmp; + /* fetch the available cpus/mems and find out which changed how */ cpumask_copy(&new_cpus, cpu_active_mask); new_mems = node_states[N_MEMORY];