freezer, sched: Report frozen tasks as 'D' instead of 'R'

JIRA: https://issues.redhat.com/browse/RHEL-96250

commit f718faf
Author: Chen Ridong <chenridong@huawei.com>
Date:   Tue Dec 17 00:48:18 2024 +0000

    freezer, sched: Report frozen tasks as 'D' instead of 'R'

    Before commit:

      f5d39b0 ("freezer,sched: Rewrite core freezer logic")

    the frozen task stat was reported as 'D' in cgroup v1.

    However, after rewriting the core freezer logic, the frozen task stat is
    reported as 'R'. This is confusing, especially when a task with stat of
    'S' is frozen.

    This bug can be reproduced with these steps:

            $ cd /sys/fs/cgroup/freezer/
            $ mkdir test
            $ sleep 1000 &
            [1] 739         // task whose stat is 'S'
            $ echo 739 > test/cgroup.procs
            $ echo FROZEN > test/freezer.state
            $ ps -aux | grep 739
            root     739  0.1  0.0   8376  1812 pts/0    R    10:56   0:00 sleep 1000

    As shown above, a task whose stat is 'S' was changed to 'R' when it was
    frozen.

    To solve this regression, simply maintain the same reported state as
    before the rewrite.

    [ mingo: Enhanced the changelog and comments ]

    Fixes: f5d39b0 ("freezer,sched: Rewrite core freezer logic")
    Signed-off-by: Chen Ridong <chenridong@huawei.com>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    Acked-by: Tejun Heo <tj@kernel.org>
    Acked-by: Michal Koutný <mkoutny@suse.com>
    Link: https://lore.kernel.org/r/20241217004818.3200515-1-chenridong@huaweicloud.com

Signed-off-by: Phil Auld <pauld@redhat.com>

Author: auldp

include/linux/sched.h

@@ -1709,8 +1709,9 @@ static inline unsigned int __task_state_index(unsigned int tsk_state,
 	 * We're lying here, but rather than expose a completely new task state
 	 * to userspace, we can make this appear as if the task has gone through
 	 * a regular rt_mutex_lock() call.
+	 * Report frozen tasks as uninterruptible.
 	 */
-	if (tsk_state & TASK_RTLOCK_WAIT)
+	if ((tsk_state & TASK_RTLOCK_WAIT) || (tsk_state & TASK_FROZEN))
 		state = TASK_UNINTERRUPTIBLE;
 
 	return fls(state);