On 4/5/2023 6:45 PM, Tetsuo Handa wrote:
syzbot is reporting circular locking dependency between cpu_hotplug_lock
and freezer_mutex, for commit f5d39b020809 ("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@xxxxxxxxxxxxxxxxxxxxxxxxx>
Link: https://syzkaller.appspot.com/bug?extid=c39682e86c9d84152f93
Suggested-by: Hillf Danton <hdanton@xxxxxxxx>
Fixes: f5d39b020809 ("freezer,sched: Rewrite core freezer logic")
Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
---
kernel/cgroup/legacy_freezer.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/kernel/cgroup/legacy_freezer.c b/kernel/cgroup/legacy_freezer.c
index 1b6b21851e9d..936473203a6b 100644
--- a/kernel/cgroup/legacy_freezer.c
+++ b/kernel/cgroup/legacy_freezer.c
@@ -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,
This was reported here as well
https://lore.kernel.org/lkml/90147a2b-982e-ae57-9b7c-062bee0fab07@xxxxxxxxxx/
Reviewed-by: Mukesh Ojha <quic_mojha@xxxxxxxxxxx>
--Mukesh
