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cgroup,freezer: hold cpu_hotplug_lock before freezer_mutex

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syzbot is reporting circular locking dependency between cpu_hotplug_lock
and freezer_mutex, for commit f5d39b0208 ("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: f5d39b0208 ("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>
This commit is contained in:
Tetsuo Handa 2023-04-05 22:15:32 +09:00 committed by Tejun Heo
parent 292fd843de
commit 57dcd64c7e
1 changed files with 5 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
kernel/cgroup/legacy_freezer.c
View File

@ -22,6 +22,7 @@
#include <linux/freezer.h>
#include <linux/seq_file.h>
#include <linux/mutex.h>
#include <linux/cpu.h>
/*
* A cgroup is freezing if any FREEZING flags are set. FREEZING_SELF is
@ -350,7 +351,7 @@ static void freezer_apply_state(struct freezer *freezer, bool freeze,
if (freeze) {
if (!(freezer->state & CGROUP_FREEZING))
static_branch_inc(&freezer_active);
static_branch_inc_cpuslocked(&freezer_active);
freezer->state |= state;
freeze_cgroup(freezer);
} else {
@ -361,7 +362,7 @@ static void freezer_apply_state(struct freezer *freezer, bool freeze,
if (!(freezer->state & CGROUP_FREEZING)) {
freezer->state &= ~CGROUP_FROZEN;
if (was_freezing)
static_branch_dec(&freezer_active);
static_branch_dec_cpuslocked(&freezer_active);
unfreeze_cgroup(freezer);
}
}
@ -379,6 +380,7 @@ static void freezer_change_state(struct freezer *freezer, bool freeze)
{
struct cgroup_subsys_state *pos;
cpus_read_lock();
/*
* Update all its descendants in pre-order traversal. Each
* descendant will try to inherit its parent's FREEZING state as
@ -407,6 +409,7 @@ static void freezer_change_state(struct freezer *freezer, bool freeze)
}
rcu_read_unlock();
mutex_unlock(&freezer_mutex);
cpus_read_unlock();
}
static ssize_t freezer_write(struct kernfs_open_file *of,