[Devel] [PATCH vz10] cgroup: fix css_set_lock IRQ unsafe usage in check_freeze_timeout()

[Vasileios Almpanis]

lockdep reports an inconsistent lock state involving css_set_lock,
triggered via cgroup_events_show() -> check_freeze_timeout():

  WARNING: inconsistent lock state
  inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage.

  Possible unsafe locking scenario:

        CPU0
        ----
   lock(css_set_lock);
   <Interrupt>
     lock(css_set_lock);

   *** DEADLOCK ***

The lock is currently taken with spin_lock()  in check_freeze_timeout(),
which does not disable interrupts. However, css_set_lock is also
acquired from IRQ/softirq context in RCU callbacks during task
teardown, making it unsafe to take the lock with interrupts enabled.

This can lead to a deadlock if an interrupt fires while holding
css_set_lock and attempts to re-acquire it.

Fix this by switching to spin_lock_irq() semantics via
scoped_guard(spinlock_irq, ...), ensuring interrupts are disabled
while holding css_set_lock in this path.

This matches the locking requirements of css_set_lock.

Fixes: 3cc887c3d0faa ("cgroup-v2/freezer: Print information about unfreezable process")
https://virtuozzo.atlassian.net/browse/VSTOR-127046

Signed-off-by: Vasileios Almpanis <vasileios.almpanis at virtuozzo.com>

Feature: cgroup/freeze: enhance logging
---
 kernel/cgroup/cgroup.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 040e7e36c238..376c9bbd1c41 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -4296,7 +4296,7 @@ static void check_freeze_timeout(struct cgroup *cgrp)
 	u64 freeze_jiffies;
 	int timeout;
 
-	scoped_guard(spinlock, &css_set_lock) {
+	scoped_guard(spinlock_irq, &css_set_lock) {
 		if (!test_bit(CGRP_FREEZE, &cgrp->flags) ||
 		    test_bit(CGRP_FROZEN, &cgrp->flags))
 			return;
-- 
2.43.0