On 1/3/2026 10:38 PM, 王志 wrote: > Dear Developers, > I am reporting an RCU CPU stall detected during fuzzing with Syzkaller on > Linux 6.18.0-rc. > > Technical Summary: The stall occurs on CPU 0 while executing a clone syscall. > The task was interrupted by a timer softirq which then invoked > mac80211_hwsim_beacon. The trace shows it is stuck waiting for a spinlock in > mac80211_hwsim_tx_frame_no_nl. > > Key Logs: > RCU GP Starvation: 10509 jiffies > Call Trace: native_queued_spin_lock_slowpath <- mac80211_hwsim_tx_frame_no_nl > <- hrtimer_run_softirq > Environment: [...] > native_queued_spin_lock_slowpath+0xae/0x9c0 > debug_spin_lock_before > home/wmy/Fuzzer/third_tool/linux-6.18/kernel/locking/spinlock_debug.c:87 > [inline] > do_raw_spin_lock+0x20d/0x2b0 > home/wmy/Fuzzer/third_tool/linux-6.18/kernel/locking/spinlock_debug.c:115 > mac80211_hwsim_tx_frame_no_nl.isra.0+0x6f1/0x12c0
This seems to be a case of softirq context acquiring a lock without spin_lock_bh. That explains the stall. A quick search on the mailing list showed this was fixed recently: https://lore.kernel.org/all/20251128151537.0b4006217137.I688f8b19346e94c1f8de0cdadde072054d4b861c@changeid/ Can you try the patch and see if it fixes? Also CC'ing the author of the patch. - Joel > mac80211_hwsim_tx_frame+0x1ed/0x2a0 > mac80211_hwsim_beacon_tx+0x56d/0x9e0 > __iterate_interfaces+0x2e0/0x650 > home/wmy/Fuzzer/third_tool/linux-6.18/net/mac80211/util.c:761 > ieee80211_iterate_active_interfaces_atomic+0x71/0x1b0 > home/wmy/Fuzzer/third_tool/linux-6.18/net/mac80211/util.c:797 > mac80211_hwsim_beacon+0x105/0x1b0 > __run_hrtimer > home/wmy/Fuzzer/third_tool/linux-6.18/kernel/time/hrtimer.c:1779 [inline] > __hrtimer_run_queues+0x1f5/0xb30 > home/wmy/Fuzzer/third_tool/linux-6.18/kernel/time/hrtimer.c:1841 > __hrtimer_get_next_event > home/wmy/Fuzzer/third_tool/linux-6.18/kernel/time/hrtimer.c:578 [inline] > hrtimer_update_softirq_timer > home/wmy/Fuzzer/third_tool/linux-6.18/kernel/time/hrtimer.c:1193 [inline] > hrtimer_run_softirq+0x17f/0x350 > home/wmy/Fuzzer/third_tool/linux-6.18/kernel/time/hrtimer.c:1861 > _test_bit > home/wmy/Fuzzer/third_tool/linux-6.18/include/asm-generic/bitops/instrumented-non-atomic.h:141 > [inline] > cpumask_test_cpu > home/wmy/Fuzzer/third_tool/linux-6.18/include/linux/cpumask.h:646 [inline] > cpu_online > home/wmy/Fuzzer/third_tool/linux-6.18/include/linux/cpumask.h:1205 [inline] > trace_softirq_exit > home/wmy/Fuzzer/third_tool/linux-6.18/include/trace/events/irq.h:142 [inline] > handle_softirqs+0x1d4/0x870 > home/wmy/Fuzzer/third_tool/linux-6.18/kernel/softirq.c:623 > __irq_exit_rcu+0x109/0x170 > home/wmy/Fuzzer/third_tool/linux-6.18/arch/x86/include/asm/bitops.h:202 > irq_exit_rcu+0x9/0x30 > home/wmy/Fuzzer/third_tool/linux-6.18/kernel/softirq.c:738 > sysvec_apic_timer_interrupt+0xa8/0xc0 > home/wmy/Fuzzer/third_tool/linux-6.18/arch/x86/kernel/apic/apic.c:2145 > </IRQ> > <TASK> > asm_sysvec_apic_timer_interrupt+0x1a/0x20 > home/wmy/Fuzzer/third_tool/linux-6.18/arch/x86/include/asm/idtentry.h:697 > RIP: 0010:__sanitizer_cov_trace_pc+0x4b/0x80 > home/wmy/Fuzzer/third_tool/linux-6.18/kernel/kcov.c:217 > Code: 74 1d a9 00 00 0f 00 75 16 a9 00 00 f0 00 74 05 c3 cc cc cc cc 8b 82 7c > 16 00 00 85 c0 75 05 e9 5b dc 89 09 8b 82 58 16 00 00 <83> f8 02 75 f0 48 8b > 8a 60 16 00 00 8b 92 5c 16 00 00 48 8b 01 48 > RSP: 0018:ffffc90002d47698 EFLAGS: 00000246 > RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff82075ed9 > RDX: ffff88802a758000 RSI: ffffffff82075ee7 RDI: 0000000000000007 > RBP: dffffc0000000000 R08: 0000000000000001 R09: fffff940002a92c6 > R10: 0000000000000000 R11: 0000000000000000 R12: ffffea0001549630 > R13: ffffea0001549600 R14: ffffea0001549618 R15: ffffea0001549600 > copy_pte_range home/wmy/Fuzzer/third_tool/linux-6.18/mm/memory.c:1284 > [inline] > copy_pmd_range home/wmy/Fuzzer/third_tool/linux-6.18/mm/memory.c:1390 > [inline] > copy_pud_range home/wmy/Fuzzer/third_tool/linux-6.18/mm/memory.c:1427 > [inline] > copy_p4d_range home/wmy/Fuzzer/third_tool/linux-6.18/mm/memory.c:1451 > [inline] > copy_page_range+0x1c67/0x63a0 > home/wmy/Fuzzer/third_tool/linux-6.18/mm/memory.c:1539 > rwsem_assert_held_write > home/wmy/Fuzzer/third_tool/linux-6.18/include/linux/rwsem.h:215 [inline] > mmap_assert_write_locked > home/wmy/Fuzzer/third_tool/linux-6.18/include/linux/mmap_lock.h:76 [inline] > vma_end_write_all > home/wmy/Fuzzer/third_tool/linux-6.18/include/linux/mmap_lock.h:347 [inline] > mmap_write_unlock > home/wmy/Fuzzer/third_tool/linux-6.18/include/linux/mmap_lock.h:354 [inline] > dup_mmap+0xd9e/0x20d0 home/wmy/Fuzzer/third_tool/linux-6.18/mm/mmap.c:1872 > futex_init_task > home/wmy/Fuzzer/third_tool/linux-6.18/include/linux/futex.h:73 [inline] > copy_process+0x36ba/0x76c0 > home/wmy/Fuzzer/third_tool/linux-6.18/kernel/fork.c:2230 > kernel_clone+0xea/0x8b0 > home/wmy/Fuzzer/third_tool/linux-6.18/kernel/fork.c:2609 > __do_sys_clone+0xce/0x120 > home/wmy/Fuzzer/third_tool/linux-6.18/kernel/fork.c:2750 > do_syscall_64+0xcb/0xfa0 > home/wmy/Fuzzer/third_tool/linux-6.18/arch/x86/entry/syscall_64.c:99 > entry_SYSCALL_64_after_hwframe+0x77/0x7f > RIP: 0033:0x7f00649a6d07 > Code: 00 00 90 f3 0f 1e fa 64 48 8b 04 25 10 00 00 00 45 31 c0 31 d2 31 f6 bf > 11 00 20 01 4c 8d 90 d0 02 00 00 b8 38 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 > 41 41 89 c0 85 c0 75 2c 64 48 8b 04 25 10 00 > RSP: 002b:00007ffe2d0a2b98 EFLAGS: 00000246 ORIG_RAX: 0000000000000038 > RAX: ffffffffffffffda RBX: 00007f006575d680 RCX: 00007f00649a6d07 > RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000001200011 > RBP: 0000000000000001 R08: 0000000000000000 R09: 0000000000000001 > R10: 0000555572e6d7d0 R11: 0000000000000246 R12: 0000000000000000 > R13: 0000000000000032 R14: 00007ffe2d0a2d80 R15: 00000000000e717e > </TASK> > rcu: rcu_preempt kthread starved for 10509 jiffies! g98817 f0x0 > RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=0 > 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 running task stack:28520 pid:16 tgid:16 > ppid:2 task_flags:0x208040 flags:0x00080000 > Call Trace: > <TASK> > sched_info_arrive > home/wmy/Fuzzer/third_tool/linux-6.18/kernel/sched/stats.h:267 [inline] > sched_info_switch > home/wmy/Fuzzer/third_tool/linux-6.18/kernel/sched/stats.h:330 [inline] > prepare_task_switch > home/wmy/Fuzzer/third_tool/linux-6.18/kernel/sched/core.c:5122 [inline] > context_switch > home/wmy/Fuzzer/third_tool/linux-6.18/kernel/sched/core.c:5272 [inline] > __schedule+0x1044/0x5bb0 > home/wmy/Fuzzer/third_tool/linux-6.18/kernel/sched/core.c:6929 > __schedule_loop > home/wmy/Fuzzer/third_tool/linux-6.18/kernel/sched/core.c:7011 [inline] > schedule+0xe7/0x3a0 > home/wmy/Fuzzer/third_tool/linux-6.18/kernel/sched/core.c:7026 > schedule_timeout+0x113/0x280 > home/wmy/Fuzzer/third_tool/linux-6.18/kernel/time/sleep_timeout.c:98 > rcu_gp_fqs_check_wake > home/wmy/Fuzzer/third_tool/linux-6.18/kernel/rcu/tree.c:2007 [inline] > rcu_gp_fqs_loop+0x18c/0xa00 > home/wmy/Fuzzer/third_tool/linux-6.18/kernel/rcu/tree.c:2083 > rcu_gp_kthread+0x26f/0x370 > home/wmy/Fuzzer/third_tool/linux-6.18/kernel/rcu/tree.c:2280 > kthread+0x3d0/0x780 > home/wmy/Fuzzer/third_tool/linux-6.18/kernel/kthread.c:463 > ret_from_fork+0x676/0x7d0 > home/wmy/Fuzzer/third_tool/linux-6.18/arch/x86/kernel/process.c:195 > ret_from_fork_asm+0x1a/0x30 > home/wmy/Fuzzer/third_tool/linux-6.18/arch/x86/entry/entry_64.S:245 > </TASK> > > Best regards, > Zhi Wang > >
