INFO: rcu detected stall in tun_chr_read_iter (2)

Status: auto-obsoleted due to no activity on 2026/06/09 17:56
Subsystems: net bpf
Labels: prio:high
[Documentation on labels]
First crash: 306d, last: 159d
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ID Workflow Result Correct Bug Created Started Finished Revision
c34899c0 assessment-security DenialOfService: ✅ Exploitable: ❌ FilesystemTrigger: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ✅ UserNamespace: ✅ VMGuestTrigger: ❌ VMHostTrigger: ❌ ❓ INFO: rcu detected stall in tun_chr_read_iter (2) 2026/05/24 01:55 2026/05/24 01:55 2026/05/24 02:55 c69befb3
▶ ▼ Similar bugs (3)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream INFO: rcu detected stall in tun_chr_read_iter mm cgroups 1 1 2450d 2450d 0/29 closed as invalid on 2019/12/04 14:14
linux-5.15 INFO: rcu detected stall in tun_chr_read_iter 1 1 329d 329d 0/3 auto-obsoleted due to no activity on 2026/01/01 00:31
android-5-15 BUG: soft lockup in tun_chr_read_iter 1 1 841d 841d 0/2 auto-obsoleted due to no activity on 2024/07/28 05:11

Sample crash report:
rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	Tasks blocked on level-0 rcu_node (CPUs 0-1): P5816/1:b..l P17077/1:b..l P17083/1:b..l P16249/1:b..l
rcu: 	(detected by 1, t=10504 jiffies, g=62345, q=520 ncpus=2)
task:syz-executor    state:R  running task     stack:24184 pid:16249 tgid:16249 ppid:16237  task_flags:0x400140 flags:0x00080000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5256 [inline]
 __schedule+0x1139/0x6150 kernel/sched/core.c:6863
 preempt_schedule_common+0x44/0xc0 kernel/sched/core.c:7047
 preempt_schedule_thunk+0x16/0x30 arch/x86/entry/thunk.S:12
 __raw_spin_unlock include/linux/spinlock_api_smp.h:143 [inline]
 _raw_spin_unlock+0x3e/0x50 kernel/locking/spinlock.c:186
 spin_unlock include/linux/spinlock.h:391 [inline]
 copy_pte_range mm/memory.c:1331 [inline]
 copy_pmd_range mm/memory.c:1392 [inline]
 copy_pud_range mm/memory.c:1429 [inline]
 copy_p4d_range mm/memory.c:1453 [inline]
 copy_page_range+0x22d0/0x6780 mm/memory.c:1535
 dup_mmap+0xbea/0x20e0 mm/mmap.c:1827
 dup_mm kernel/fork.c:1529 [inline]
 copy_mm kernel/fork.c:1581 [inline]
 copy_process+0x3b9f/0x7430 kernel/fork.c:2221
 kernel_clone+0xfc/0x910 kernel/fork.c:2651
 __do_sys_clone+0xce/0x120 kernel/fork.c:2792
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f8921985e93
RSP: 002b:00007ffd27a70268 EFLAGS: 00000246 ORIG_RAX: 0000000000000038
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f8921985e93
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000001200011
RBP: 0000000000000001 R08: 0000000000000000 R09: 0000000000000001
R10: 000055556df567d0 R11: 0000000000000246 R12: 0000000000000000
R13: 00000000000927c0 R14: 000000000012b16e R15: 00007ffd27a70400
 </TASK>
task:syz-executor    state:R  running task     stack:28488 pid:17083 tgid:17083 ppid:5810   task_flags:0x400040 flags:0x00080000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5256 [inline]
 __schedule+0x1139/0x6150 kernel/sched/core.c:6863
 preempt_schedule_irq+0x51/0x90 kernel/sched/core.c:7190
 irqentry_exit+0x1d8/0x8c0 kernel/entry/common.c:216
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697
RIP: 0010:lock_acquire+0x62/0x330 kernel/locking/lockdep.c:5872
Code: 66 18 12 83 f8 07 0f 87 a2 02 00 00 89 c0 48 0f a3 05 82 88 ee 0e 0f 82 74 02 00 00 8b 35 1a b9 ee 0e 85 f6 0f 85 8d 00 00 00 <48> 8b 44 24 30 65 48 2b 05 99 66 18 12 0f 85 ad 02 00 00 48 83 c4
RSP: 0018:ffffc90003e875b8 EFLAGS: 00000206
RAX: 0000000000000046 RBX: ffffffff8e3c9620 RCX: 0000000068c1bacb
RDX: 0000000000000000 RSI: ffffffff8daa5ce7 RDI: ffffffff8bf2a880
RBP: 0000000000000002 R08: 00000000ffffffff R09: 00000000ffffffff
R10: 0000000000000002 R11: ffff888083500b30 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
 rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
 rcu_read_lock include/linux/rcupdate.h:867 [inline]
 class_rcu_constructor include/linux/rcupdate.h:1195 [inline]
 unwind_next_frame+0xd1/0x20a0 arch/x86/kernel/unwind_orc.c:479
 arch_stack_walk+0x94/0x100 arch/x86/kernel/stacktrace.c:25
 stack_trace_save+0x8e/0xc0 kernel/stacktrace.c:122
 kasan_save_stack+0x33/0x60 mm/kasan/common.c:56
 kasan_save_track+0x14/0x30 mm/kasan/common.c:77
 kasan_save_free_info+0x3b/0x60 mm/kasan/generic.c:584
 poison_slab_object mm/kasan/common.c:252 [inline]
 __kasan_slab_free+0x5f/0x80 mm/kasan/common.c:284
 kasan_slab_free include/linux/kasan.h:234 [inline]
 slab_free_hook mm/slub.c:2540 [inline]
 slab_free mm/slub.c:6668 [inline]
 kmem_cache_free+0x2d8/0x770 mm/slub.c:6779
 kfree_skbmem+0x1a4/0x1f0 net/core/skbuff.c:1130
 __kfree_skb net/core/skbuff.c:1197 [inline]
 consume_skb net/core/skbuff.c:1428 [inline]
 consume_skb+0xcc/0x100 net/core/skbuff.c:1422
 tun_do_read+0xd31/0x1d00 drivers/net/tun.c:2188
 tun_chr_read_iter+0x101/0x290 drivers/net/tun.c:2208
 new_sync_read fs/read_write.c:491 [inline]
 vfs_read+0x8bf/0xcf0 fs/read_write.c:572
 ksys_read+0x12a/0x250 fs/read_write.c:715
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f1b9318e15c
RSP: 002b:00007ffc8acbe030 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
RAX: ffffffffffffffda RBX: 00007ffc8acbe060 RCX: 00007f1b9318e15c
RDX: 00000000000003e8 RSI: 00007ffc8acbe060 RDI: 00000000000000c8
RBP: 00007ffc8acbe49c R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000236
R13: 00000000000927c0 R14: 000000000012b308 R15: 00007ffc8acbe4f0
 </TASK>
task:modprobe        state:R  running task     stack:24936 pid:17077 tgid:17077 ppid:14223  task_flags:0x400000 flags:0x00080000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5256 [inline]
 __schedule+0x1139/0x6150 kernel/sched/core.c:6863
 preempt_schedule_irq+0x51/0x90 kernel/sched/core.c:7190
 irqentry_exit+0x1d8/0x8c0 kernel/entry/common.c:216
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697
RIP: 0010:lock_release+0x183/0x2d0 kernel/locking/lockdep.c:5893
Code: 0f c1 05 58 b3 18 12 83 f8 01 0f 85 03 01 00 00 9c 58 f6 c4 02 0f 85 ee 00 00 00 41 f7 c5 00 02 00 00 74 01 fb 48 8b 44 24 10 <65> 48 2b 05 ed 6b 18 12 0f 85 32 01 00 00 48 83 c4 18 5b 41 5c 41
RSP: 0018:ffffc90003247890 EFLAGS: 00000206
RAX: 6cc116e8ad9b1900 RBX: ffffffff8e3c9620 RCX: ffffc9000324789c
RDX: 0000000000000000 RSI: ffffffff8daa5ce7 RDI: ffffffff8bf2a880
RBP: 0000000000000001 R08: 0000000000000001 R09: 00000000ffffffff
R10: 0000000000000002 R11: 0000000000013ef5 R12: ffffffff816cb9a4
R13: 0000000000000206 R14: ffff88802c9a4980 R15: 0000000000000001
 rcu_lock_release include/linux/rcupdate.h:341 [inline]
 rcu_read_unlock include/linux/rcupdate.h:897 [inline]
 class_rcu_destructor include/linux/rcupdate.h:1195 [inline]
 unwind_next_frame+0x3f9/0x20a0 arch/x86/kernel/unwind_orc.c:479
 arch_stack_walk+0x94/0x100 arch/x86/kernel/stacktrace.c:25
 stack_trace_save+0x8e/0xc0 kernel/stacktrace.c:122
 kasan_save_stack+0x33/0x60 mm/kasan/common.c:56
 kasan_save_track+0x14/0x30 mm/kasan/common.c:77
 unpoison_slab_object mm/kasan/common.c:339 [inline]
 __kasan_slab_alloc+0x89/0x90 mm/kasan/common.c:365
 kasan_slab_alloc include/linux/kasan.h:252 [inline]
 slab_post_alloc_hook mm/slub.c:4953 [inline]
 slab_alloc_node mm/slub.c:5263 [inline]
 kmem_cache_alloc_noprof+0x25e/0x770 mm/slub.c:5270
 getname_flags.part.0+0x4c/0x550 fs/namei.c:146
 getname_flags+0x93/0xf0 include/linux/audit.h:345
 getname include/linux/fs.h:2498 [inline]
 do_sys_openat2+0xb9/0x290 fs/open.c:1426
 do_sys_open fs/open.c:1436 [inline]
 __do_sys_openat fs/open.c:1452 [inline]
 __se_sys_openat fs/open.c:1447 [inline]
 __x64_sys_openat+0x174/0x210 fs/open.c:1447
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fd21401a0ba
RSP: 002b:00007ffc400e33e8 EFLAGS: 00000206 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 00007ffc400e3460 RCX: 00007fd21401a0ba
RDX: 0000000000080000 RSI: 00007ffc400e3460 RDI: 00000000ffffff9c
RBP: 00007ffc400e3450 R08: 00007ffc400e3657 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000206 R12: 0000000000000017
R13: 00007fd213fee000 R14: 00007ffc400e3670 R15: 0000000000000000
 </TASK>
task:syz-executor    state:R  running task     stack:23864 pid:5816  tgid:5816  ppid:5808   task_flags:0x400140 flags:0x00080000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5256 [inline]
 __schedule+0x1139/0x6150 kernel/sched/core.c:6863
 preempt_schedule_common+0x44/0xc0 kernel/sched/core.c:7047
 preempt_schedule_thunk+0x16/0x30 arch/x86/entry/thunk.S:12
 __raw_spin_unlock include/linux/spinlock_api_smp.h:143 [inline]
 _raw_spin_unlock+0x3e/0x50 kernel/locking/spinlock.c:186
 spin_unlock include/linux/spinlock.h:391 [inline]
 copy_pte_range mm/memory.c:1331 [inline]
 copy_pmd_range mm/memory.c:1392 [inline]
 copy_pud_range mm/memory.c:1429 [inline]
 copy_p4d_range mm/memory.c:1453 [inline]
 copy_page_range+0x22d0/0x6780 mm/memory.c:1535
 dup_mmap+0xbea/0x20e0 mm/mmap.c:1827
 dup_mm kernel/fork.c:1529 [inline]
 copy_mm kernel/fork.c:1581 [inline]
 copy_process+0x3b9f/0x7430 kernel/fork.c:2221
 kernel_clone+0xfc/0x910 kernel/fork.c:2651
 __do_sys_clone+0xce/0x120 kernel/fork.c:2792
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fee65585e93
RSP: 002b:00007fff0bf77ab8 EFLAGS: 00000246 ORIG_RAX: 0000000000000038
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fee65585e93
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000001200011
RBP: 0000000000000001 R08: 0000000000000000 R09: 0000000000000001
R10: 0000555593bf77d0 R11: 0000000000000246 R12: 0000000000000000
R13: 00000000000927c0 R14: 000000000012b2ea R15: 00007fff0bf77c50
 </TASK>
rcu: rcu_preempt kthread starved for 10490 jiffies! g62345 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=1
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:27512 pid:16    tgid:16    ppid:2      task_flags:0x208040 flags:0x00080000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5256 [inline]
 __schedule+0x1139/0x6150 kernel/sched/core.c:6863
 __schedule_loop kernel/sched/core.c:6945 [inline]
 schedule+0xe7/0x3a0 kernel/sched/core.c:6960
 schedule_timeout+0x123/0x290 kernel/time/sleep_timeout.c:99
 rcu_gp_fqs_loop+0x1ea/0xaf0 kernel/rcu/tree.c:2083
 rcu_gp_kthread+0x26d/0x380 kernel/rcu/tree.c:2285
 kthread+0x3c5/0x780 kernel/kthread.c:463
 ret_from_fork+0x983/0xb10 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
 </TASK>
rcu: Stack dump where RCU GP kthread last ran:
CPU: 1 UID: 0 PID: 4413 Comm: kworker/u8:15 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Workqueue: events_unbound toggle_allocation_gate
RIP: 0010:csd_lock_wait kernel/smp.c:342 [inline]
RIP: 0010:smp_call_function_many_cond+0xdfd/0x15e0 kernel/smp.c:877
Code: 57 48 8b 54 24 10 4c 89 74 24 10 49 89 d5 48 89 d5 48 89 54 24 18 49 c1 ed 03 83 e5 07 4d 01 e5 83 c5 03 e8 b5 5a 0c 00 f3 90 <41> 0f b6 45 00 40 38 c5 7c 08 84 c0 0f 85 b6 05 00 00 8b 43 08 31
RSP: 0018:ffffc9000eb87808 EFLAGS: 00000293
RAX: 0000000000000000 RBX: ffff8880b84431e0 RCX: ffffffff81b28971
RDX: ffff888035574980 RSI: ffffffff81b2894b RDI: 0000000000000005
RBP: 0000000000000003 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000000000001 R11: ffff8880355754b0 R12: dffffc0000000000
R13: ffffed101708863d R14: 0000000000000001 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff8881249fa000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000002000 CR3: 000000000e184000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 on_each_cpu_cond_mask+0x40/0x90 kernel/smp.c:1043
 on_each_cpu include/linux/smp.h:71 [inline]
 smp_text_poke_sync_each_cpu arch/x86/kernel/alternative.c:2711 [inline]
 smp_text_poke_batch_finish+0x27b/0xdb0 arch/x86/kernel/alternative.c:2921
 arch_jump_label_transform_apply+0x1c/0x30 arch/x86/kernel/jump_label.c:146
 jump_label_update+0x376/0x550 kernel/jump_label.c:919
 static_key_enable_cpuslocked+0x1b7/0x270 kernel/jump_label.c:210
 static_key_enable+0x1a/0x20 kernel/jump_label.c:223
 toggle_allocation_gate mm/kfence/core.c:874 [inline]
 toggle_allocation_gate+0xfa/0x280 mm/kfence/core.c:866
 process_one_work+0x9ba/0x1b20 kernel/workqueue.c:3257
 process_scheduled_works kernel/workqueue.c:3340 [inline]
 worker_thread+0x6c8/0xf10 kernel/workqueue.c:3421
 kthread+0x3c5/0x780 kernel/kthread.c:463
 ret_from_fork+0x983/0xb10 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
 </TASK>

Crashes (4):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/12/13 21:35 upstream 4a298a43f5e3 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root INFO: rcu detected stall in tun_chr_read_iter
2026/03/11 17:46 net 908c344d5cfa 2d88ab01 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-net-this-kasan-gce INFO: rcu detected stall in tun_chr_read_iter
2025/10/16 01:18 net bfdd74166a63 19568248 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-net-this-kasan-gce INFO: rcu detected stall in tun_chr_read_iter
2025/12/27 09:32 linux-next cc3aa43b44bd d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root INFO: rcu detected stall in tun_chr_read_iter
* Struck through repros no longer work on HEAD.