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INFO: task hung in __cgroup_procs_write

Status: upstream: reported C repro on 2025/09/23 17:05
Bug presence: origin:upstream
[Documentation on labels]
Reported-by: syzbot+437d8a0d5b72c5b27315@syzkaller.appspotmail.com
First crash: 111d, last: 12h32m
▶ ▼ Bug presence (1)
Date Name Commit Repro Result
2025/09/26 upstream (ToT) 4ff71af020ae C [report] INFO: task hung in exit_mmap
▶ ▼ Similar bugs (2)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream INFO: task hung in __cgroup_procs_write cgroups 1 2 551d 569d 0/29 auto-obsoleted due to no activity on 2024/10/08 12:21
linux-6.1 INFO: task hung in __cgroup_procs_write origin:upstream 1 syz 2 2d01h 32d 0/3 upstream: reported syz repro on 2025/12/11 21:53
▶ ▼ Last patch testing requests (7)
Created Duration User Patch Repo Result
2026/01/04 07:30 19m retest repro linux-5.15.y report log
2026/01/02 06:39 21m retest repro linux-5.15.y report log
2025/12/26 12:35 13m retest repro linux-5.15.y report log
2025/12/25 20:39 12m retest repro linux-5.15.y report log
2025/10/25 16:34 16m retest repro linux-5.15.y report log
2025/10/23 18:21 14m retest repro linux-5.15.y report log
2025/10/23 18:21 12m retest repro linux-5.15.y report log
▶ ▼ Fix bisection attempts (1)
Created Duration User Patch Repo Result
2025/11/14 23:07 1h56m bisect fix linux-5.15.y OK (0) job log log

Sample crash report:
INFO: task syz-executor:4323 blocked for more than 143 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz-executor    state:D stack:20352 pid: 4323 ppid:  4318 flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5049 [inline]
 __schedule+0x11bb/0x4390 kernel/sched/core.c:6395
 schedule+0x11b/0x1e0 kernel/sched/core.c:6478
 schedule_preempt_disabled+0xf/0x20 kernel/sched/core.c:6537
 __mutex_lock_common+0xc71/0x2390 kernel/locking/mutex.c:669
 __mutex_lock kernel/locking/mutex.c:729 [inline]
 mutex_lock_nested+0x17/0x20 kernel/locking/mutex.c:743
 cgroup_kn_lock_live+0xee/0x230 kernel/cgroup/cgroup.c:1662
 __cgroup_procs_write+0x73/0x350 kernel/cgroup/cgroup.c:5012
 cgroup_procs_write+0x23/0x40 kernel/cgroup/cgroup.c:5052
 cgroup_file_write+0x2f7/0x630 kernel/cgroup/cgroup.c:3966
 kernfs_fop_write_iter+0x379/0x4c0 fs/kernfs/file.c:296
 call_write_iter include/linux/fs.h:2173 [inline]
 new_sync_write fs/read_write.c:507 [inline]
 vfs_write+0x712/0xd00 fs/read_write.c:594
 ksys_write+0x14d/0x250 fs/read_write.c:647
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f4bfb7391ff
RSP: 002b:00007ffd18b47e00 EFLAGS: 00000293 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007f4bfb7391ff
RDX: 0000000000000001 RSI: 00007ffd18b47e50 RDI: 0000000000000003
RBP: 00007ffd18b483c0 R08: 0000000000000000 R09: 00007ffd18b47c57
R10: 0000000000000000 R11: 0000000000000293 R12: 0000000000000001
R13: 00007ffd18b47e50 R14: 00007ffd18b48380 R15: 00007ffd18b483c0
 </TASK>
INFO: task syz-executor:4324 blocked for more than 143 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz-executor    state:D stack:21888 pid: 4324 ppid:  4320 flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5049 [inline]
 __schedule+0x11bb/0x4390 kernel/sched/core.c:6395
 schedule+0x11b/0x1e0 kernel/sched/core.c:6478
 rwsem_down_write_slowpath+0xc46/0x11f0 kernel/locking/rwsem.c:1165
 mmap_write_lock include/linux/mmap_lock.h:71 [inline]
 mpol_rebind_mm+0x33/0x2c0 mm/mempolicy.c:381
 cpuset_attach+0x330/0x5f0 kernel/cgroup/cpuset.c:2376
 cgroup_migrate_execute+0x7eb/0x1010 kernel/cgroup/cgroup.c:2597
 cgroup_attach_task+0x562/0x7e0 kernel/cgroup/cgroup.c:2892
 __cgroup1_procs_write+0x2e5/0x3f0 kernel/cgroup/cgroup-v1.c:527
 cgroup_file_write+0x2f7/0x630 kernel/cgroup/cgroup.c:3966
 kernfs_fop_write_iter+0x379/0x4c0 fs/kernfs/file.c:296
 call_write_iter include/linux/fs.h:2173 [inline]
 new_sync_write fs/read_write.c:507 [inline]
 vfs_write+0x712/0xd00 fs/read_write.c:594
 ksys_write+0x14d/0x250 fs/read_write.c:647
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f61c44611ff
RSP: 002b:00007ffee16a6230 EFLAGS: 00000293 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007f61c44611ff
RDX: 0000000000000001 RSI: 00007ffee16a6280 RDI: 0000000000000003
RBP: 00007ffee16a67f0 R08: 0000000000000000 R09: 00007ffee16a6087
R10: 0000000000000000 R11: 0000000000000293 R12: 0000000000000001
R13: 00007ffee16a6280 R14: 00007ffee16a67b0 R15: 00007ffee16a67f0
 </TASK>
INFO: task syz-executor:4332 blocked for more than 143 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz-executor    state:D stack:19976 pid: 4332 ppid:  4326 flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5049 [inline]
 __schedule+0x11bb/0x4390 kernel/sched/core.c:6395
 schedule+0x11b/0x1e0 kernel/sched/core.c:6478
 schedule_preempt_disabled+0xf/0x20 kernel/sched/core.c:6537
 __mutex_lock_common+0xc71/0x2390 kernel/locking/mutex.c:669
 __mutex_lock kernel/locking/mutex.c:729 [inline]
 mutex_lock_nested+0x17/0x20 kernel/locking/mutex.c:743
 cgroup_kn_lock_live+0xee/0x230 kernel/cgroup/cgroup.c:1662
 __cgroup_procs_write+0x73/0x350 kernel/cgroup/cgroup.c:5012
 cgroup_procs_write+0x23/0x40 kernel/cgroup/cgroup.c:5052
 cgroup_file_write+0x2f7/0x630 kernel/cgroup/cgroup.c:3966
 kernfs_fop_write_iter+0x379/0x4c0 fs/kernfs/file.c:296
 call_write_iter include/linux/fs.h:2173 [inline]
 new_sync_write fs/read_write.c:507 [inline]
 vfs_write+0x712/0xd00 fs/read_write.c:594
 ksys_write+0x14d/0x250 fs/read_write.c:647
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f88a79011ff
RSP: 002b:00007ffd59adc290 EFLAGS: 00000293 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007f88a79011ff
RDX: 0000000000000001 RSI: 00007ffd59adc2e0 RDI: 0000000000000003
RBP: 00007ffd59adc850 R08: 0000000000000000 R09: 00007ffd59adc0e7
R10: 0000000000000000 R11: 0000000000000293 R12: 0000000000000001
R13: 00007ffd59adc2e0 R14: 00007ffd59adc810 R15: 00007ffd59adc850
 </TASK>

Showing all locks held in the system:
1 lock held by khungtaskd/27:
 #0: ffffffff8c11c720 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x0/0x30
2 locks held by kworker/u4:3/155:
1 lock held by dhcpcd/3853:
 #0: ffffffff8c1421b0 (cgroup_threadgroup_rwsem){++++}-{0:0}, at: copy_process+0x2290/0x3e00 kernel/fork.c:2382
2 locks held by getty/3946:
 #0: ffff88814cb3c098 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x21/0x70 drivers/tty/tty_ldisc.c:252
 #1: ffffc90002cf62e8 (&ldata->atomic_read_lock){+.+.}-{3:3}, at: n_tty_read+0x5ba/0x1a30 drivers/tty/n_tty.c:2158
1 lock held by udevd/4234:
 #0: ffffffff8c1421b0 (cgroup_threadgroup_rwsem){++++}-{0:0}, at: do_exit+0x256/0x20a0 kernel/exit.c:830
1 lock held by syz-executor/4317:
 #0: ffffffff8c1421b0 (cgroup_threadgroup_rwsem){++++}-{0:0}, at: do_exit+0x256/0x20a0 kernel/exit.c:830
2 locks held by syz-executor/4319:
 #0: ffffffff8c1a68b0 (dup_mmap_sem){.+.+}-{0:0}, at: dup_mmap kernel/fork.c:503 [inline]
 #0: ffffffff8c1a68b0 (dup_mmap_sem){.+.+}-{0:0}, at: dup_mm kernel/fork.c:1466 [inline]
 #0: ffffffff8c1a68b0 (dup_mmap_sem){.+.+}-{0:0}, at: copy_mm+0x21f/0x1380 kernel/fork.c:1518
 #1: ffff88801686f128 (&mm->mmap_lock){++++}-{3:3}, at: mmap_write_lock_killable include/linux/mmap_lock.h:87 [inline]
 #1: ffff88801686f128 (&mm->mmap_lock){++++}-{3:3}, at: dup_mmap kernel/fork.c:504 [inline]
 #1: ffff88801686f128 (&mm->mmap_lock){++++}-{3:3}, at: dup_mm kernel/fork.c:1466 [inline]
 #1: ffff88801686f128 (&mm->mmap_lock){++++}-{3:3}, at: copy_mm+0x238/0x1380 kernel/fork.c:1518
3 locks held by syz-executor/4323:
 #0: ffff888018fac460 (sb_writers#10){.+.+}-{0:0}, at: vfs_write+0x28a/0xd00 fs/read_write.c:590
 #1: ffff88805bf7f488 (&of->mutex){+.+.}-{3:3}, at: kernfs_fop_write_iter+0x1e5/0x4c0 fs/kernfs/file.c:287
 #2: ffffffff8c141fc8 (cgroup_mutex){+.+.}-{3:3}, at: cgroup_kn_lock_live+0xee/0x230 kernel/cgroup/cgroup.c:1662
7 locks held by syz-executor/4324:
 #0: ffff88801b914460 (sb_writers#11){.+.+}-{0:0}, at: vfs_write+0x28a/0xd00 fs/read_write.c:590
 #1: ffff88807a143088 (&of->mutex){+.+.}-{3:3}, at: kernfs_fop_write_iter+0x1e5/0x4c0 fs/kernfs/file.c:287
 #2: ffffffff8c141fc8 (cgroup_mutex){+.+.}-{3:3}, at: cgroup_kn_lock_live+0xee/0x230 kernel/cgroup/cgroup.c:1662
 #3: ffffffff8bfbae90 (cpu_hotplug_lock){++++}-{0:0}, at: cgroup_attach_lock kernel/cgroup/cgroup.c:2411 [inline]
 #3: ffffffff8bfbae90 (cpu_hotplug_lock){++++}-{0:0}, at: cgroup_procs_write_start+0x17c/0x580 kernel/cgroup/cgroup.c:2921
 #4: ffffffff8c1421b0 (cgroup_threadgroup_rwsem){++++}-{0:0}, at: cgroup_attach_lock kernel/cgroup/cgroup.c:2413 [inline]
 #4: ffffffff8c1421b0 (cgroup_threadgroup_rwsem){++++}-{0:0}, at: cgroup_procs_write_start+0x192/0x580 kernel/cgroup/cgroup.c:2921
 #5: ffffffff8c14fb08 (cpuset_mutex){+.+.}-{3:3}, at: cpuset_attach+0xac/0x5f0 kernel/cgroup/cpuset.c:2348
 #6: ffff88802b393928 (&mm->mmap_lock){++++}-{3:3}, at: mmap_write_lock include/linux/mmap_lock.h:71 [inline]
 #6: ffff88802b393928 (&mm->mmap_lock){++++}-{3:3}, at: mpol_rebind_mm+0x33/0x2c0 mm/mempolicy.c:381
2 locks held by syz-executor/4325:
 #0: ffffffff8c1a68b0 (dup_mmap_sem){.+.+}-{0:0}, at: dup_mmap kernel/fork.c:503 [inline]
 #0: ffffffff8c1a68b0 (dup_mmap_sem){.+.+}-{0:0}, at: dup_mm kernel/fork.c:1466 [inline]
 #0: ffffffff8c1a68b0 (dup_mmap_sem){.+.+}-{0:0}, at: copy_mm+0x21f/0x1380 kernel/fork.c:1518
 #1: ffff88801686ea28 (&mm->mmap_lock){++++}-{3:3}, at: mmap_write_lock_killable include/linux/mmap_lock.h:87 [inline]
 #1: ffff88801686ea28 (&mm->mmap_lock){++++}-{3:3}, at: dup_mmap kernel/fork.c:504 [inline]
 #1: ffff88801686ea28 (&mm->mmap_lock){++++}-{3:3}, at: dup_mm kernel/fork.c:1466 [inline]
 #1: ffff88801686ea28 (&mm->mmap_lock){++++}-{3:3}, at: copy_mm+0x238/0x1380 kernel/fork.c:1518
1 lock held by udevd/4328:
 #0: ffffffff8c1421b0 (cgroup_threadgroup_rwsem){++++}-{0:0}, at: do_exit+0x256/0x20a0 kernel/exit.c:830
3 locks held by syz-executor/4332:
 #0: ffff888018fac460 (sb_writers#10){.+.+}-{0:0}, at: vfs_write+0x28a/0xd00 fs/read_write.c:590
 #1: ffff88805bf7c088 (&of->mutex){+.+.}-{3:3}, at: kernfs_fop_write_iter+0x1e5/0x4c0 fs/kernfs/file.c:287
 #2: ffffffff8c141fc8 (cgroup_mutex){+.+.}-{3:3}, at: cgroup_kn_lock_live+0xee/0x230 kernel/cgroup/cgroup.c:1662
1 lock held by udevd/4337:
 #0: ffffffff8c1421b0 (cgroup_threadgroup_rwsem){++++}-{0:0}, at: do_exit+0x256/0x20a0 kernel/exit.c:830
1 lock held by udevd/4338:
 #0: ffffffff8c1421b0 (cgroup_threadgroup_rwsem){++++}-{0:0}, at: do_exit+0x256/0x20a0 kernel/exit.c:830
1 lock held by udevd/4339:
 #0: ffffffff8c1421b0 (cgroup_threadgroup_rwsem){++++}-{0:0}, at: do_exit+0x256/0x20a0 kernel/exit.c:830
2 locks held by kworker/u4:7/4415:

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

NMI backtrace for cpu 1
CPU: 1 PID: 27 Comm: khungtaskd Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x168/0x230 lib/dump_stack.c:106
 nmi_cpu_backtrace+0x397/0x3d0 lib/nmi_backtrace.c:111
 nmi_trigger_cpumask_backtrace+0x163/0x280 lib/nmi_backtrace.c:62
 trigger_all_cpu_backtrace include/linux/nmi.h:148 [inline]
 check_hung_uninterruptible_tasks kernel/hung_task.c:212 [inline]
 watchdog+0xe0f/0xe50 kernel/hung_task.c:369
 kthread+0x436/0x520 kernel/kthread.c:334
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
 </TASK>
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 154 Comm: kworker/u4:2 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Workqueue: phy10 ieee80211_iface_work (phy13)
RIP: 0010:process_one_work+0x4e3/0x1000 kernel/workqueue.c:2252
Code: 0f 85 1f 08 00 00 41 89 5e 28 49 8d 5e 74 48 8b 44 24 58 42 80 3c 20 00 74 08 4c 89 ff e8 65 ef 6d 00 be 60 01 00 00 49 03 37 <ba> 18 00 00 00 48 89 df e8 30 3f af 02 48 8b 5c 24 10 4c 8d 7b 08
RSP: 0018:ffffc90001e87c40 EFLAGS: 00000086
RAX: 1ffff110054abe81 RBX: ffff88801d24a074 RCX: 1ffff11003a49405
RDX: 0000000000000000 RSI: ffff888024077160 RDI: 00000000ffffffff
RBP: ffffc90001e87db8 R08: dffffc0000000000 R09: fffffbfff2c697f7
R10: fffffbfff2c697f7 R11: 1ffffffff2c697f6 R12: dffffc0000000000
R13: ffff88801d24a018 R14: ffff88801d24a000 R15: ffff88802a55f408
FS:  0000000000000000(0000) GS:ffff8880b9000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f93bbf967c0 CR3: 000000007e6b1000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 worker_thread+0xaa8/0x12a0 kernel/workqueue.c:2457
 kthread+0x436/0x520 kernel/kthread.c:334
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
 </TASK>

Crashes (12):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/01/12 18:06 linux-5.15.y 68efe5a6c16a d6526ea3 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf INFO: task hung in __cgroup_procs_write
2026/01/11 23:09 linux-5.15.y 68efe5a6c16a d6526ea3 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan INFO: task hung in __cgroup_procs_write
2026/01/11 16:58 linux-5.15.y 68efe5a6c16a d6526ea3 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan INFO: task hung in __cgroup_procs_write
2026/01/10 18:26 linux-5.15.y 68efe5a6c16a d6526ea3 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan INFO: task hung in __cgroup_procs_write
2025/09/24 11:35 linux-5.15.y 43bb85222e53 0abd0691 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf INFO: task hung in __cgroup_procs_write
2026/01/12 13:27 linux-5.15.y 68efe5a6c16a d6526ea3 .config console log report syz / log [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf INFO: task hung in __cgroup_procs_write
2025/12/11 19:54 linux-5.15.y 68efe5a6c16a d6526ea3 .config console log report syz / log [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf INFO: task hung in __cgroup_procs_write
2025/12/06 08:40 linux-5.15.y cc5ec8769306 d6526ea3 .config console log report syz / log [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan INFO: task hung in __cgroup_procs_write
2025/10/09 17:17 linux-5.15.y 29e53a5b1c4f 7e2882b3 .config console log report syz / log [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf INFO: task hung in __cgroup_procs_write
2025/10/09 11:46 linux-5.15.y 29e53a5b1c4f 7e2882b3 .config console log report syz / log [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan INFO: task hung in __cgroup_procs_write
2025/10/07 22:43 linux-5.15.y 29e53a5b1c4f 7e2882b3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf INFO: task hung in __cgroup_procs_write
2025/09/23 17:04 linux-5.15.y 43bb85222e53 e667a34f .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf INFO: task hung in __cgroup_procs_write
* Struck through repros no longer work on HEAD.