Question: What is CVE-2025-21657?
Answer: CVE-2025-21657 is a vulnerability classified as nan with a CVSS score of nan. It falls under nan and affects the system as follows: In the Linux kernel, the following vulnerability has been resolved:

sched_ext: Replace rq_lock() to raw_spin_rq_lock() in scx_ops_bypass()

scx_ops_bypass() iterates all CPUs to re-enqueue all the scx tasks.
For each CPU, it acquires a lock using rq_lock() regardless of whether
a CPU is offline or the CPU is currently running a task in a higher
scheduler class (e.g., deadline). The rq_lock() is supposed to be used
for online CPUs, and the use of rq_lock() may trigger an unnecessary
warning in rq_pin_lock(). Therefore, replace rq_lock() to
raw_spin_rq_lock() in scx_ops_bypass().

Without this change, we observe the following warning:

===== START =====
[    6.615205] rq->balance_callback && rq->balance_callback != &balance_push_callback
[    6.615208] WARNING: CPU: 2 PID: 0 at kernel/sched/sched.h:1730 __schedule+0x1130/0x1c90
=====  END  =====