INFO: task hung in sb_start_write (2)

Status: upstream: reported C repro on 2025/05/23 04:46
Subsystems: kernfs ext4
Labels: prio:high
[Documentation on labels]
Reported-by: syzbot+b3fba2e269970207b61d@syzkaller.appspotmail.com
First crash: 538d, last: 2d05h
✨ AI Patch Versions (1)
Version Stage Reported Report Link Job
1 moderation 2026/08/07 15:35 Discussion 1f731a02-676c-4f22-a26c-1ff8c1dd0a49
✨ AI Jobs (3)
ID Workflow Result Correct Bug Created Started Finished Revision
1f731a02 patching INFO: task hung in sb_start_write (2) 2026/08/07 14:14 2026/08/07 14:14 2026/08/07 15:35 e4ef95d6
6ed4a942 repro-c Reproduced: ✅
INFO: task hung in sb_start_write (2) 2026/08/05 17:32 2026/08/07 01:38 2026/08/07 02:33 c38879ea
67d6f14d assessment-security DenialOfService: ✅ Exploitable: ❌ FilesystemTrigger: ✅ NetworkTrigger: ❌ PeripheralTrigger: ✅ RemoteTrigger: ❌ Unprivileged: ❌ UserNamespace: ❌ VMGuestTrigger: ❌ VMHostTrigger: ❌ INFO: task hung in sb_start_write (2) 2026/05/24 06:48 2026/05/24 06:48 2026/05/24 07:36 c69befb3
Discussions (5)
Title Replies (including bot) Last reply
[syzbot] [jfs?] [xfs?] [bcachefs?] INFO: task hung in sb_start_write (2) 0 (2) 2026/08/07 09:21
[syzbot] Monthly kernfs report (Aug 2026) 0 (1) 2026/08/02 00:00
[syzbot] Monthly kernfs report (Aug 2025) 0 (1) 2025/08/23 16:32
[syzbot] Monthly f2fs report (Aug 2025) 0 (1) 2025/08/01 13:49
[syzbot] Monthly f2fs report (Jul 2025) 0 (1) 2025/07/01 09:24
Similar bugs (3)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream INFO: task hung in sb_start_write ext4 xfs 1 516 667d 745d 0/29 auto-obsoleted due to no activity on 2024/12/19 19:32
linux-6.1 INFO: task hung in sb_start_write 1 4 741d 752d 0/3 auto-obsoleted due to no activity on 2024/11/05 17:25
linux-5.15 INFO: task hung in sb_start_write 1 2 700d 744d 0/3 auto-obsoleted due to no activity on 2024/12/17 04:15
Last patch testing requests (1)
Created Duration User Patch Repo Result
2026/08/07 08:07 1h04m nogikh@google.com upstream report log
Cause bisection attempts (1)
Created Duration User Patch Repo Result
2026/08/09 13:47 0m bisect upstream error

Sample crash report:
INFO: task syz-executor328:5959 blocked for more than 15 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz-executor328 state:D stack:28328 pid:5959  tgid:5959  ppid:5947   task_flags:0x400040 flags:0x00080000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5510 [inline]
 __schedule+0x16dc/0x5500 kernel/sched/core.c:7234
 __schedule_loop kernel/sched/core.c:7311 [inline]
 schedule+0x164/0x2b0 kernel/sched/core.c:7326
 percpu_rwsem_wait+0x32d/0x4a0 kernel/locking/percpu-rwsem.c:164
 __percpu_down_read+0xf8/0x140 kernel/locking/percpu-rwsem.c:180
 percpu_down_read_internal include/linux/percpu-rwsem.h:67 [inline]
 percpu_down_read_freezable include/linux/percpu-rwsem.h:83 [inline]
 __sb_start_write include/linux/fs/super.h:19 [inline]
 sb_start_write+0x18e/0x1c0 include/linux/fs/super.h:125
 mnt_want_write+0x41/0x90 fs/namespace.c:494
 do_tmpfile+0x6c/0x240 fs/namei.c:4817
 path_openat+0x3095/0x3850 fs/namei.c:4854
 do_file_open+0x23e/0x4a0 fs/namei.c:4892
 do_sys_openat2+0x115/0x200 fs/open.c:1368
 do_sys_open fs/open.c:1374 [inline]
 __do_sys_openat fs/open.c:1390 [inline]
 __se_sys_openat fs/open.c:1385 [inline]
 __x64_sys_openat+0x138/0x170 fs/open.c:1385
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f3fb490aaf7
RSP: 002b:00007fff7f2f6f10 EFLAGS: 00000202 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 0000555578a51400 RCX: 00007f3fb490aaf7
RDX: 0000000000410001 RSI: 00007f3fb494a764 RDI: ffffffffffffff9c
RBP: 00007f3fb494a764 R08: 0000000000000000 R09: 0000000000000000
R10: 00000000000001b6 R11: 0000000000000202 R12: 00007fff7f2f70d8
R13: 0000000000000002 R14: 00007f3fb4970c80 R15: 0000000000000002
 </TASK>

Showing all locks held in the system:
1 lock held by khungtaskd/38:
 #0: ffffffff8e1c3000 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
 #0: ffffffff8e1c3000 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:840 [inline]
 #0: ffffffff8e1c3000 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x2e/0x180 kernel/locking/lockdep.c:6775
2 locks held by getty/5356:
 #0: ffff88803688d0a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:243
 #1: ffffc90003cc62e0 (&ldata->atomic_read_lock){+.+.}-{4:4}, at: n_tty_read+0x460/0x1360 drivers/tty/n_tty.c:2211
1 lock held by syz-executor328/5959:
 #0: ffff888035a88500 (sb_writers#4){++++}-{0:0}, at: mnt_want_write+0x41/0x90 fs/namespace.c:494

=============================================

NMI backtrace for cpu 1
CPU: 1 UID: 0 PID: 38 Comm: khungtaskd Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 nmi_cpu_backtrace+0x274/0x2d0 lib/nmi_backtrace.c:122
 nmi_trigger_cpumask_backtrace+0x17a/0x380 lib/nmi_backtrace.c:65
 trigger_all_cpu_backtrace include/linux/nmi.h:162 [inline]
 __sys_info lib/sys_info.c:157 [inline]
 sys_info+0x135/0x170 lib/sys_info.c:165
 check_hung_uninterruptible_tasks kernel/hung_task.c:353 [inline]
 watchdog+0xfd7/0x1030 kernel/hung_task.c:561
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
RIP: 0010:pv_native_safe_halt+0xf/0x20 arch/x86/kernel/paravirt.c:64
Code: cb 6e 02 e9 13 cf 03 00 cc cc cc 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 66 90 0f 00 2d 33 44 24 00 fb f4 <c3> cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc 90 90 90 90 90
RSP: 0018:ffffffff8de07de0 EFLAGS: 00000242
RAX: 000000000009a1e9 RBX: ffffffff81998590 RCX: 0000000080000001
RDX: 0000000000000001 RSI: ffffffff8d887e30 RDI: ffffffff8bca6d80
RBP: ffffffff8de07eb8 R08: ffff8880b8633d5b R09: 1ffff110170c67ab
R10: dffffc0000000000 R11: ffffed10170c67ac R12: 0000000000000000
R13: 1ffffffff1bdede8 R14: 1ffffffff1bc0fc4 R15: dffffc0000000000
FS:  0000000000000000(0000) GS:ffff888125c36000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000563216b981d0 CR3: 000000000dfb0000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 arch_safe_halt arch/x86/kernel/process.c:767 [inline]
 default_idle+0x9/0x20 arch/x86/kernel/process.c:768
 default_idle_call+0x72/0xb0 kernel/sched/idle.c:122
 cpuidle_idle_call kernel/sched/idle.c:199 [inline]
 do_idle+0x2e0/0x540 kernel/sched/idle.c:355
 cpu_startup_entry+0x43/0x60 kernel/sched/idle.c:454
 rest_init+0x2de/0x300 init/main.c:717
 start_kernel+0x392/0x3e0 init/main.c:1175
 x86_64_start_reservations+0x24/0x30 arch/x86/kernel/head64.c:310
 x86_64_start_kernel+0x137/0x1b0 arch/x86/kernel/head64.c:291
 common_startup_64+0x13e/0x157
 </TASK>

Crashes (132):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/08/07 09:20 upstream f9a2394a2348 de6a700d .config console log report C ci2-upstream-fs INFO: task hung in sb_start_write
2026/07/21 07:35 upstream b95f03f04d47 de6a700d .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in sb_start_write
2026/06/14 09:09 upstream 2b07ea76fd28 1d2f3589 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in sb_start_write
2026/06/06 16:12 upstream 8e65320d91cd cc095639 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in sb_start_write
2026/05/21 06:34 upstream 8bc67e4db64a 41b8c833 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in sb_start_write
2026/05/19 06:03 upstream 4d3a2a466b8d 9f74d399 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in sb_start_write
2026/05/16 02:45 upstream d458a240344c 81fb92f3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in sb_start_write
2026/05/12 09:17 upstream 50897c955902 07aeade5 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in sb_start_write
2026/04/09 08:14 upstream 7f87a5ea75f0 38c8e246 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in sb_start_write
2026/03/08 15:51 upstream c23719abc330 5cb44a80 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in sb_start_write
2026/03/07 00:03 upstream 651690480a96 41d8037d .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in sb_start_write
2026/02/22 10:23 upstream fa5c82f4d2bb 6e7b5511 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in sb_start_write
2026/02/17 01:31 upstream c22e26bd0906 5d52cba5 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in sb_start_write
2026/02/08 07:19 upstream e7aa57247700 4c131dc4 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in sb_start_write
2026/01/20 14:35 upstream 24d479d26b25 06648d9c .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in sb_start_write
2026/01/18 10:15 upstream d12453c7e281 20d37d28 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in sb_start_write
2026/01/18 06:21 upstream d12453c7e281 20d37d28 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in sb_start_write
2026/01/17 23:44 upstream d3eeb99bbc99 20d37d28 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in sb_start_write
2026/01/17 16:18 upstream d3eeb99bbc99 20d37d28 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in sb_start_write
2026/01/16 09:45 upstream 603c05a1639f d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in sb_start_write
2026/01/16 07:14 upstream 603c05a1639f d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in sb_start_write
2026/01/15 19:48 upstream 944aacb68baf d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in sb_start_write
2026/01/15 06:15 upstream 944aacb68baf d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in sb_start_write
2026/01/13 16:54 upstream b71e635feefc d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in sb_start_write
2026/01/10 06:01 upstream 372800cb95a3 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in sb_start_write
2026/01/09 16:46 upstream 623fb9912f6a d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in sb_start_write
2026/01/08 01:08 upstream f0b9d8eb98df d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in sb_start_write
2026/01/07 16:35 upstream f0b9d8eb98df d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in sb_start_write
2026/01/07 06:50 upstream f0b9d8eb98df d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in sb_start_write
2026/01/07 03:40 upstream f0b9d8eb98df d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in sb_start_write
2026/01/07 00:04 upstream f0b9d8eb98df d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in sb_start_write
2026/01/06 17:13 upstream 7f98ab9da046 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in sb_start_write
2026/01/06 11:47 upstream 7f98ab9da046 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in sb_start_write
2026/01/06 08:10 upstream 7f98ab9da046 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in sb_start_write
2026/01/01 10:13 upstream 349bd28a86f2 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in sb_start_write
2025/12/31 16:39 upstream c8ebd433459b d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in sb_start_write
2025/12/31 00:58 upstream dbf8fe85a16a d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in sb_start_write
2025/12/28 18:19 upstream d26143bb38e2 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in sb_start_write
2025/12/28 09:28 upstream d26143bb38e2 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in sb_start_write
2025/12/27 22:47 upstream c53f467229a7 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in sb_start_write
2025/12/27 04:28 upstream 3f0e9c8cefa9 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in sb_start_write
2025/12/26 19:36 upstream ccd1cdca5cd4 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in sb_start_write
2025/12/26 06:20 upstream ccd1cdca5cd4 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in sb_start_write
2025/12/25 22:06 upstream ccd1cdca5cd4 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in sb_start_write
2025/12/25 13:33 upstream ccd1cdca5cd4 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in sb_start_write
2025/05/19 04:38 upstream a5806cd506af f41472b0 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in sb_start_write
2025/05/11 12:57 upstream 3ce9925823c7 77908e5f .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in sb_start_write
2025/12/02 04:57 linux-next 7d31f578f323 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root INFO: task hung in sb_start_write
2025/03/11 02:36 git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci 0a6021b3fc20 16256247 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-gce-arm64 INFO: task hung in sb_start_write
* Struck through repros no longer work on HEAD.