cgroup,freezer: hold cpu_hotplug_lock before freezer_mutex
syzbot is reporting circular locking dependency between cpu_hotplug_lock and freezer_mutex, for commit f5d39b02 ("freezer,sched: Rewrite core freezer logic") replaced atomic_inc() in freezer_apply_state() with static_branch_inc() which holds cpu_hotplug_lock. cpu_hotplug_lock => cgroup_threadgroup_rwsem => freezer_mutex cgroup_file_write() { cgroup_procs_write() { __cgroup_procs_write() { cgroup_procs_write_start() { cgroup_attach_lock() { cpus_read_lock() { percpu_down_read(&cpu_hotplug_lock); } percpu_down_write(&cgroup_threadgroup_rwsem); } } cgroup_attach_task() { cgroup_migrate() { cgroup_migrate_execute() { freezer_attach() { mutex_lock(&freezer_mutex); (...snipped...) } } } } (...snipped...) } } } freezer_mutex => cpu_hotplug_lock cgroup_file_write() { freezer_write() { freezer_change_state() { mutex_lock(&freezer_mutex); freezer_apply_state() { static_branch_inc(&freezer_active) { static_key_slow_inc() { cpus_read_lock(); static_key_slow_inc_cpuslocked(); cpus_read_unlock(); } } } mutex_unlock(&freezer_mutex); } } } Swap locking order by moving cpus_read_lock() in freezer_apply_state() to before mutex_lock(&freezer_mutex) in freezer_change_state(). Reported-by:syzbot <syzbot+c39682e86c9d84152f93@syzkaller.appspotmail.com> Link: https://syzkaller.appspot.com/bug?extid=c39682e86c9d84152f93 Suggested-by:
Hillf Danton <hdanton@sina.com> Fixes: f5d39b02 ("freezer,sched: Rewrite core freezer logic") Signed-off-by:
Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Acked-by:
Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by:
Mukesh Ojha <quic_mojha@quicinc.com> Signed-off-by:
Tejun Heo <tj@kernel.org>
parent
292fd843