INFO: rcu detected stall in sys_sendto

Status: upstream: reported C repro on 2025/08/26 10:53
Bug presence: origin:lts-only
[Documentation on labels]
Reported-by: syzbot+65b7d080de37a0d45cc4@syzkaller.appspotmail.com
First crash: 345d, last: 11d
▶ ▼ Bug presence (2)
Date Name Commit Repro Result
2026/02/21 linux-6.6.y (ToT) 7a137e9bfa0e C [report] INFO: rcu detected stall in corrupted
2026/02/21 upstream (ToT) d79526b89571 C Didn't crash
▶ ▼ Similar bugs (13)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream INFO: rcu detected stall in sys_sendto (2) mm 1 93 2402d 2403d 0/29 closed as dup on 2020/01/08 06:15
upstream INFO: rcu detected stall in sys_sendto (6) net 1 1 987d 987d 0/29 closed as invalid on 2024/02/01 10:31
linux-6.1 INFO: rcu detected stall in sys_sendto origin:upstream 1 syz, C error 1 700d 923d 0/3 auto-obsoleted due to no activity on 2025/10/30 02:21
linux-5.15 INFO: rcu detected stall in sys_sendto 1 1 723d 723d 0/3 auto-obsoleted due to no activity on 2024/11/22 09:09
upstream INFO: rcu detected stall in sys_sendto mm 1 357 2437d 2439d 0/29 closed as invalid on 2019/12/04 14:14
upstream INFO: rcu detected stall in sys_sendto (7) prio:low wireless mm 1 syz, C error error 402 8d04h 807d 0/29 upstream: reported C repro on 2024/05/21 18:44
upstream INFO: rcu detected stall in sys_sendto (5) perf 1 7 1649d 1770d 0/29 closed as invalid on 2022/02/08 10:00
upstream INFO: rcu detected stall in sys_sendto (4) perf 1 1 2228d 2228d 0/29 auto-closed as invalid on 2020/09/29 07:17
linux-5.15 INFO: rcu detected stall in sys_sendto (2) origin:lts-only 1 syz done 2 522d 614d 0/3 upstream: reported syz repro on 2024/12/01 03:42
upstream INFO: rcu detected stall in sys_sendto (3) kernel 1 1 2305d 2305d 0/29 closed as invalid on 2020/05/21 18:32
linux-6.1 INFO: rcu detected stall in sys_sendto (2) origin:upstream 1 syz error 3 15d 237d 0/3 upstream: reported syz repro on 2025/12/12 19:08
android-5-10 BUG: soft lockup in sys_sendto 1 2 1086d 1123d 0/2 auto-obsoleted due to no activity on 2023/11/14 13:19
android-5-15 BUG: soft lockup in sys_sendto 1 1 779d 779d 0/2 auto-obsoleted due to no activity on 2024/09/16 21:53
▶ ▼ Fix bisection attempts (4)
Created Duration User Patch Repo Result
2026/06/08 21:56 19m fix candidate upstream error job log
2026/05/05 06:53 21m fix candidate upstream error job log
2026/03/24 17:55 6m fix candidate upstream error job log
2026/02/21 21:29 0m fix candidate upstream error job log

Sample crash report:
rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	Tasks blocked on level-0 rcu_node (CPUs 0-1): P5885/1:b..l P5139/1:b..l
rcu: 	(detected by 1, t=10502 jiffies, g=12497, q=531 ncpus=2)
task:udevd           state:R  running task     stack:25160 pid:5139  ppid:1      flags:0x00004002
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5381 [inline]
 __schedule+0x1553/0x45a0 kernel/sched/core.c:6700
 preempt_schedule_common+0x82/0xc0 kernel/sched/core.c:6867
 preempt_schedule+0xc0/0xd0 kernel/sched/core.c:6891
 preempt_schedule_thunk+0x1a/0x30 arch/x86/entry/thunk_64.S:45
 __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:152 [inline]
 _raw_spin_unlock_irqrestore+0x111/0x120 kernel/locking/spinlock.c:194
 spin_unlock_irqrestore include/linux/spinlock.h:406 [inline]
 __wake_up_common_lock kernel/sched/wait.c:140 [inline]
 __wake_up_sync_key+0x12c/0x1a0 kernel/sched/wait.c:213
 sock_def_readable+0x1e1/0x420 net/core/sock.c:3354
 __netlink_sendskb net/netlink/af_netlink.c:1266 [inline]
 netlink_sendskb+0x9b/0x130 net/netlink/af_netlink.c:1272
 netlink_sendmsg+0x8d0/0xbf0 net/netlink/af_netlink.c:1894
 sock_sendmsg_nosec net/socket.c:730 [inline]
 __sock_sendmsg net/socket.c:745 [inline]
 ____sys_sendmsg+0x5ba/0x960 net/socket.c:2594
 ___sys_sendmsg+0x2a6/0x360 net/socket.c:2648
 __sys_sendmsg net/socket.c:2677 [inline]
 __do_sys_sendmsg net/socket.c:2686 [inline]
 __se_sys_sendmsg+0x1c2/0x2b0 net/socket.c:2684
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x55/0xa0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f92e6ea7407
RSP: 002b:00007ffea3cb6dc0 EFLAGS: 00000202 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007f92e7578880 RCX: 00007f92e6ea7407
RDX: 0000000000000000 RSI: 00007ffea3cb6e20 RDI: 0000000000000004
RBP: 0000555aa5eccab0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 00000000000000b3
R13: 0000555aa5e579e0 R14: 0000000000000000 R15: 0000000000000000
 </TASK>
task:syz-executor    state:R  running task     stack:21704 pid:5885  ppid:5883   flags:0x00004002
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5381 [inline]
 __schedule+0x1553/0x45a0 kernel/sched/core.c:6700
 preempt_schedule_irq+0xbf/0x150 kernel/sched/core.c:7010
 irqentry_exit+0x67/0x70 kernel/entry/common.c:438
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:687
RIP: 0010:ipv6_store_devconf net/ipv6/addrconf.c:5637 [inline]
RIP: 0010:inet6_fill_ifla6_attrs+0x522/0x21f0 net/ipv6/addrconf.c:5816
Code: 8d bd 04 06 00 00 4c 89 f8 48 c1 e8 03 42 0f b6 04 30 84 c0 0f 85 98 10 00 00 49 63 3f e8 36 21 3b f8 4d 8d bc 24 b0 00 00 00 <4c> 89 f9 48 c1 e9 03 42 0f b6 0c 31 84 c9 0f 85 92 10 00 00 41 89
RSP: 0018:ffffc900036e6980 EFLAGS: 00000202
RAX: 000000000036ee80 RBX: 00000000ffffffff RCX: ffff888023f33c00
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000057e40
RBP: ffffc900036e6aa0 R08: ffff88807db50413 R09: 0000000000000000
R10: ffff88807db50328 R11: ffffed100fb6a083 R12: ffff88807db50324
R13: ffff8880771a6000 R14: dffffc0000000000 R15: ffff88807db503d4
 inet6_fill_link_af+0x9b/0x120 net/ipv6/addrconf.c:5862
 rtnl_fill_link_af+0x1c2/0x430 net/core/rtnetlink.c:1701
 rtnl_fill_ifinfo+0x1bb6/0x1e50 net/core/rtnetlink.c:1931
 rtmsg_ifinfo_build_skb+0x18e/0x260 net/core/rtnetlink.c:4072
 rtmsg_ifinfo_event net/core/rtnetlink.c:4106 [inline]
 rtmsg_ifinfo+0x8c/0x1a0 net/core/rtnetlink.c:4115
 register_netdevice+0x17b8/0x1bb0 net/core/dev.c:10340
 cfg80211_register_netdevice+0x159/0x2f0 net/wireless/core.c:1457
 ieee80211_if_add+0xa1b/0x14e0 net/mac80211/iface.c:2270
 ieee80211_register_hw+0x35ca/0x4250 net/mac80211/main.c:1441
 mac80211_hwsim_new_radio+0x2a00/0x4d10 drivers/net/wireless/virtual/mac80211_hwsim.c:5307
 hwsim_new_radio_nl+0xdc9/0x1a90 drivers/net/wireless/virtual/mac80211_hwsim.c:5988
 genl_family_rcv_msg_doit+0x211/0x310 net/netlink/genetlink.c:971
 genl_family_rcv_msg net/netlink/genetlink.c:1051 [inline]
 genl_rcv_msg+0x619/0x7a0 net/netlink/genetlink.c:1066
 netlink_rcv_skb+0x241/0x4d0 net/netlink/af_netlink.c:2545
 genl_rcv+0x28/0x40 net/netlink/genetlink.c:1075
 netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
 netlink_unicast+0x751/0x8d0 net/netlink/af_netlink.c:1346
 netlink_sendmsg+0x8d0/0xbf0 net/netlink/af_netlink.c:1894
 sock_sendmsg_nosec net/socket.c:730 [inline]
 __sock_sendmsg net/socket.c:745 [inline]
 __sys_sendto+0x4a9/0x6b0 net/socket.c:2200
 __do_sys_sendto net/socket.c:2212 [inline]
 __se_sys_sendto net/socket.c:2208 [inline]
 __x64_sys_sendto+0xde/0xf0 net/socket.c:2208
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x55/0xa0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fb34955cece
RSP: 002b:00007ffe9d4ffb38 EFLAGS: 00000246 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 000055555bba5500 RCX: 00007fb34955cece
RDX: 0000000000000024 RSI: 00007fb34a344670 RDI: 0000000000000003
RBP: 0000000000000001 R08: 00007ffe9d4ffbb4 R09: 000000000000000c
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000003
R13: 0000000000000000 R14: 00007fb34a344670 R15: 0000000000000000
 </TASK>
rcu: rcu_preempt kthread starved for 10583 jiffies! g12497 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:27656 pid:17    ppid:2      flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5381 [inline]
 __schedule+0x1553/0x45a0 kernel/sched/core.c:6700
 schedule+0xbd/0x170 kernel/sched/core.c:6774
 schedule_timeout+0x188/0x2d0 kernel/time/timer.c:2168
 rcu_gp_fqs_loop+0x313/0x1590 kernel/rcu/tree.c:1667
 rcu_gp_kthread+0x9d/0x3b0 kernel/rcu/tree.c:1866
 kthread+0x2fa/0x390 kernel/kthread.c:388
 ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293
 </TASK>
rcu: Stack dump where RCU GP kthread last ran:
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 5754 Comm: kworker/0:3 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Workqueue: events nsim_fib_event_work
RIP: 0010:__debug_check_no_obj_freed lib/debugobjects.c:-1 [inline]
RIP: 0010:debug_check_no_obj_freed+0x1e6/0x540 lib/debugobjects.c:1020
Code: 0f 84 40 03 00 00 49 89 ee 49 c1 ee 03 41 80 3c 16 00 74 12 48 89 ef e8 38 a1 ae fd 48 ba 00 00 00 00 00 fc ff df 48 8b 45 00 <48> 89 04 24 4c 8d 7d 18 4c 89 f8 48 c1 e8 03 80 3c 10 00 74 12 4c
RSP: 0018:ffffc900046af4f0 EFLAGS: 00000046
RAX: ffff88802e0bb3b8 RBX: 0000000000000000 RCX: 0000000000000001
RDX: dffffc0000000000 RSI: 0000000000000004 RDI: ffffc900046af3e0
RBP: ffff8880605e4dc8 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffff520008d5e7c R12: ffff88807a9d8000
R13: ffff88807a9d0000 R14: 1ffff1100c0bc9b9 R15: 0000000000000004
FS:  0000000000000000(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000020000006b000 CR3: 000000002c609000 CR4: 00000000003506f0
Call Trace:
 <TASK>
 free_pages_prepare mm/page_alloc.c:1187 [inline]
 free_unref_page_prepare+0x1da/0x8c0 mm/page_alloc.c:2365
 free_unref_page+0x32/0x2e0 mm/page_alloc.c:2458
 __slab_free+0x35a/0x400 mm/slub.c:3736
 qlink_free mm/kasan/quarantine.c:166 [inline]
 qlist_free_all+0x75/0xd0 mm/kasan/quarantine.c:185
 kasan_quarantine_reduce+0x143/0x160 mm/kasan/quarantine.c:292
 __kasan_slab_alloc+0x22/0x80 mm/kasan/common.c:306
 kasan_slab_alloc include/linux/kasan.h:188 [inline]
 slab_post_alloc_hook+0x6e/0x4b0 mm/slab.h:767
 slab_alloc_node mm/slub.c:3495 [inline]
 __kmem_cache_alloc_node+0x13a/0x250 mm/slub.c:3534
 kmalloc_trace+0x2a/0xe0 mm/slab_common.c:1098
 kmalloc include/linux/slab.h:600 [inline]
 kzalloc include/linux/slab.h:721 [inline]
 nsim_fib6_rt_create drivers/net/netdevsim/fib.c:547 [inline]
 nsim_fib6_rt_insert drivers/net/netdevsim/fib.c:752 [inline]
 nsim_fib6_event drivers/net/netdevsim/fib.c:856 [inline]
 nsim_fib_event drivers/net/netdevsim/fib.c:889 [inline]
 nsim_fib_event_work+0x1123/0x31b0 drivers/net/netdevsim/fib.c:1494
 process_one_work kernel/workqueue.c:2634 [inline]
 process_scheduled_works+0xa5d/0x15d0 kernel/workqueue.c:2711
 worker_thread+0xa55/0xfc0 kernel/workqueue.c:2792
 kthread+0x2fa/0x390 kernel/kthread.c:388
 ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293
 </TASK>

Crashes (8):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/02/21 13:12 linux-6.6.y 7a137e9bfa0e 6e7b5511 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan INFO: rcu detected stall in sys_sendto
2026/07/26 22:39 linux-6.6.y c5596480c50e 492bab15 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan-perf INFO: rcu detected stall in sys_sendto
2026/04/15 15:37 linux-6.6.y 8cee53b8eaeb c441f497 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan-perf INFO: rcu detected stall in sys_sendto
2026/04/13 04:46 linux-6.6.y 8cee53b8eaeb 38c8e246 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan-perf INFO: rcu detected stall in sys_sendto
2026/01/05 10:17 linux-6.6.y 5fa4793a2d2d d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan-perf INFO: rcu detected stall in sys_sendto
2025/12/18 05:01 linux-6.6.y 5fa4793a2d2d d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan-perf INFO: rcu detected stall in sys_sendto
2025/10/01 01:54 linux-6.6.y 147338df3487 65a0eece .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan INFO: rcu detected stall in sys_sendto
2025/08/26 10:53 linux-6.6.y bb9c90ab9c5a bf27483f .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan INFO: rcu detected stall in sys_sendto
* Struck through repros no longer work on HEAD.