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Message-ID: <69c25468.bb2e.19ba83c1775.Coremail.wangzhi_xd@stu.xidian.edu.cn> Date: Sat, 10 Jan 2026 22:07:49 +0800 (GMT+08:00) From: 王志 <wangzhi_xd@....xidian.edu.cn> To: "Paul E. McKenney" <paulmck@...nel.org>, "Frederic Weisbecker" <frederic@...nel.org> Cc: linux-kernel@...r.kernel.org, rcu@...r.kernel.org Subject: [BUG] rcu: rcu_preempt detected stalls (starved for 10498 jiffies) in drm_vblank_disable_and_save Dear Maintainers, When using our customized Syzkaller to fuzz the latest Linux kernel, the following crash was triggered. HEAD commit: 7d0a66e4bb9081d75c82ec4957c50034cb0ea449 git tree: upstream Output: https://github.com/manual0/crash/blob/main/report2.txt Kernel config: https://github.com/manual0/crash/blob/main/config.txt C reproducer: https://github.com/manual0/crash/blob/main/repro2.c Syz reproducer: https://github.com/manual0/crash/blob/main/repro2.syz Brief Introduction: The kernel reports an RCU CPU stall (rcu_preempt detected stalls). The rcu_preempt kthread was starved for 10,498 jiffies, which usually leads to an expected OOM. The NMI backtrace shows CPU 3 is spinning in the lockdep/locking code while attempting to cancel an hrtimer during a timer softirq. The call path originates from drm_vblank_disable_and_save and reaches hrtimer_cancel_wait_running. This suggests a potential deadlock or an excessively long critical section in the DRM vblank/timer handling path that prevents the RCU grace-period kthread from being scheduled on that CPU. If you fix this issue, please add the following tag to the commit: Reported-by: Zhi Wang <wangzhi@....xidian.edu.cn>, Bin Yu<byu@...ian.edu.cn>, MingYu Wang<w15303746062@....com>, WenJian Lu<19861702678@....com>, KeFeng Gao<2401553064@...com> Relevant Log: rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: rcu: (detected by 0, t=10502 jiffies, g=64625, q=212 ncpus=4) rcu: All QSes seen, last rcu_preempt kthread activity 10498 (4295006777-4294996279), jiffies_till_next_fqs=1, root ->qsmask 0x0 rcu: rcu_preempt kthread timer wakeup didn't happen for 10497 jiffies! g64625 f0x2 RCU_GP_WAIT_FQS(5) ->state=0x200 rcu: Possible timer handling issue on cpu=3 timer-softirq=24641 rcu: rcu_preempt kthread starved for 10498 jiffies! g64625 f0x2 RCU_GP_WAIT_FQS(5) ->state=0x200 ->cpu=3 rcu: Unless rcu_preempt kthread gets sufficient CPU time, OOM is now expected behavior. rcu: RCU grace-period kthread stack dump: task:rcu_preempt state:R stack:28920 pid:16 tgid:16 ppid:2 task_flags:0x208040 flags:0x00080000 Call Trace: <TASK> sched_info_arrive home/linux-6.18/kernel/sched/stats.h:267 [inline] sched_info_switch home/linux-6.18/kernel/sched/stats.h:330 [inline] prepare_task_switch home/linux-6.18/kernel/sched/core.c:5122 [inline] context_switch home/inux-6.18/kernel/sched/core.c:5272 [inline] __schedule+0x1044/0x5bb0 home/linux-6.18/kernel/sched/core.c:6929 __schedule_loop home/linux-6.18/kernel/sched/core.c:7011 [inline] schedule+0xe7/0x3a0 home/linux-6.18/kernel/sched/core.c:7026 schedule_timeout+0x113/0x280 home/linux-6.18/kernel/time/sleep_timeout.c:98 rcu_gp_fqs_check_wake home/linux-6.18/kernel/rcu/tree.c:2007 [inline] rcu_gp_fqs_loop+0x18c/0xa00 home/linux-6.18/kernel/rcu/tree.c:2083 rcu_gp_kthread+0x26f/0x370 home/linux-6.18/kernel/rcu/tree.c:2280 kthread+0x3d0/0x780 home/linux-6.18/kernel/kthread.c:463 ret_from_fork+0x676/0x7d0 home/linux-6.18/arch/x86/kernel/process.c:195 ret_from_fork_asm+0x1a/0x30 home/linux-6.18/arch/x86/entry/entry_64.S:245 </TASK> Thanks, Zhi Wang
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