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cgroup/cpuset: Call is_in_v2_mode() after acquiring cpuset_mutex in cpuset_handle_hotplug()

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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: b8d1b8ee93 ("cpuset: Allow v2 behavior in v1 cgroup")
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Waiman Long 2026-10-05 06:43:10 -04:00 committed by Tejun Heo
parent 23b1ab15ca
commit b8eb5fd5bd
1 changed files with 5 additions and 4 deletions
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9
kernel/cgroup/cpuset.c
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@ -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];