syzbot


INFO: task hung in mpol_rebind_mm

Status: upstream: reported C repro on 2025/09/28 22:17
Bug presence: origin:upstream
[Documentation on labels]
Reported-by: syzbot+bbd2c8637e67cf4b529c@syzkaller.appspotmail.com
First crash: 34d, last: 1d06h
Bug presence (1)
Date Name Commit Repro Result
2025/09/30 upstream (ToT) e129e479f2e4 C [report] INFO: task hung in exit_mmap
Similar bugs (2)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-6.1 INFO: task hung in mpol_rebind_mm 1 1 365d 365d 0/3 auto-obsoleted due to no activity on 2025/02/09 04:47
linux-6.1 INFO: task hung in mpol_rebind_mm (2) origin:upstream 1 C 6 8d19h 39d 0/3 upstream: reported C repro on 2025/09/23 07:26

Sample crash report:
INFO: task syz-executor:4509 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:20232 pid: 4509 ppid:  4506 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:2172 [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: 0033:0x7f609703d97f
RSP: 002b:00007ffe0c2c07b0 EFLAGS: 00000293 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007f609703d97f
RDX: 0000000000000001 RSI: 00007ffe0c2c0800 RDI: 0000000000000003
RBP: 00007ffe0c2c0d70 R08: 0000000000000000 R09: 00007ffe0c2c0607
R10: 0000000000000000 R11: 0000000000000293 R12: 0000000000000001
R13: 00007ffe0c2c0800 R14: 00007ffe0c2c0d30 R15: 00007ffe0c2c0d70
 </TASK>

Showing all locks held in the system:
1 lock held by khungtaskd/27:
 #0: ffffffff8c11c660 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x0/0x30
4 locks held by kworker/u4:1/144:
 #0: ffff8880169cd938 ((wq_completion)netns){+.+.}-{0:0}, at: process_one_work+0x760/0x1000 kernel/workqueue.c:-1
 #1: ffffc900010afd00 (net_cleanup_work){+.+.}-{0:0}, at: process_one_work+0x7a3/0x1000 kernel/workqueue.c:2285
 #2: ffffffff8d22c690 (pernet_ops_rwsem){++++}-{3:3}, at: cleanup_net+0x132/0xb80 net/core/net_namespace.c:589
 #3: ffff888073ccd3e8 (&wg->device_update_lock){+.+.}-{3:3}, at: wg_destruct+0x112/0x300 drivers/net/wireguard/device.c:233
2 locks held by kworker/u4:4/1391:
 #0: ffff888016879138 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_one_work+0x760/0x1000 kernel/workqueue.c:-1
 #1: ffffc900054e7d00 ((work_completion)(&sub_info->work)){+.+.}-{0:0}, at: process_one_work+0x7a3/0x1000 kernel/workqueue.c:2285
1 lock held by klogd/3550:
2 locks held by udevd/3561:
 #0: ffffffff8c1a67f0 (dup_mmap_sem){.+.+}-{0:0}, at: dup_mmap kernel/fork.c:503 [inline]
 #0: ffffffff8c1a67f0 (dup_mmap_sem){.+.+}-{0:0}, at: dup_mm kernel/fork.c:1466 [inline]
 #0: ffffffff8c1a67f0 (dup_mmap_sem){.+.+}-{0:0}, at: copy_mm+0x21f/0x1380 kernel/fork.c:1518
 #1: ffff88807dbd1d28 (&mm->mmap_lock){++++}-{3:3}, at: mmap_write_lock_killable include/linux/mmap_lock.h:87 [inline]
 #1: ffff88807dbd1d28 (&mm->mmap_lock){++++}-{3:3}, at: dup_mmap kernel/fork.c:504 [inline]
 #1: ffff88807dbd1d28 (&mm->mmap_lock){++++}-{3:3}, at: dup_mm kernel/fork.c:1466 [inline]
 #1: ffff88807dbd1d28 (&mm->mmap_lock){++++}-{3:3}, at: copy_mm+0x238/0x1380 kernel/fork.c:1518
2 locks held by getty/3948:
 #0: ffff88802c064098 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x21/0x70 drivers/tty/tty_ldisc.c:252
 #1: ffffc900025e62e8 (&ldata->atomic_read_lock){+.+.}-{3:3}, at: n_tty_read+0x5ba/0x1a30 drivers/tty/n_tty.c:2158
1 lock held by napi/wg2-0/4375:
 #0: ffffffff8c1420f0 (cgroup_threadgroup_rwsem){++++}-{0:0}, at: do_exit+0x256/0x20a0 kernel/exit.c:830
1 lock held by modprobe/4408:
 #0: ffff8880796c7828 (&mm->mmap_lock){++++}-{3:3}, at: mmap_write_lock_killable include/linux/mmap_lock.h:87 [inline]
 #0: ffff8880796c7828 (&mm->mmap_lock){++++}-{3:3}, at: vm_mmap_pgoff+0x15d/0x2b0 mm/util.c:549
1 lock held by udevd/4412:
 #0: ffffffff8c1420f0 (cgroup_threadgroup_rwsem){++++}-{0:0}, at: do_exit+0x256/0x20a0 kernel/exit.c:830
1 lock held by syz-executor/4413:
 #0: ffffffff8c1420f0 (cgroup_threadgroup_rwsem){++++}-{0:0}, at: do_exit+0x256/0x20a0 kernel/exit.c:830
2 locks held by syz-executor/4414:
 #0: ffffffff8c1a67f0 (dup_mmap_sem){.+.+}-{0:0}, at: dup_mmap kernel/fork.c:503 [inline]
 #0: ffffffff8c1a67f0 (dup_mmap_sem){.+.+}-{0:0}, at: dup_mm kernel/fork.c:1466 [inline]
 #0: ffffffff8c1a67f0 (dup_mmap_sem){.+.+}-{0:0}, at: copy_mm+0x21f/0x1380 kernel/fork.c:1518
 #1: ffff88807e376328 (&mm->mmap_lock){++++}-{3:3}, at: mmap_write_lock_killable include/linux/mmap_lock.h:87 [inline]
 #1: ffff88807e376328 (&mm->mmap_lock){++++}-{3:3}, at: dup_mmap kernel/fork.c:504 [inline]
 #1: ffff88807e376328 (&mm->mmap_lock){++++}-{3:3}, at: dup_mm kernel/fork.c:1466 [inline]
 #1: ffff88807e376328 (&mm->mmap_lock){++++}-{3:3}, at: copy_mm+0x238/0x1380 kernel/fork.c:1518
1 lock held by udevd/4421:
 #0: ffffffff8c1420f0 (cgroup_threadgroup_rwsem){++++}-{0:0}, at: do_exit+0x256/0x20a0 kernel/exit.c:830
1 lock held by udevd/4422:
 #0: ffffffff8c1420f0 (cgroup_threadgroup_rwsem){++++}-{0:0}, at: do_exit+0x256/0x20a0 kernel/exit.c:830
1 lock held by udevd/4424:
 #0: ffffffff8c1420f0 (cgroup_threadgroup_rwsem){++++}-{0:0}, at: do_exit+0x256/0x20a0 kernel/exit.c:830
1 lock held by sed/4487:
 #0: ffff88802b7b1d28 (&mm->mmap_lock){++++}-{3:3}, at: mmap_write_lock_killable include/linux/mmap_lock.h:87 [inline]
 #0: ffff88802b7b1d28 (&mm->mmap_lock){++++}-{3:3}, at: setup_arg_pages+0x2db/0xa20 fs/exec.c:797
2 locks held by syz-executor/4491:
 #0: ffffffff8c1a67f0 (dup_mmap_sem){.+.+}-{0:0}, at: dup_mmap kernel/fork.c:503 [inline]
 #0: ffffffff8c1a67f0 (dup_mmap_sem){.+.+}-{0:0}, at: dup_mm kernel/fork.c:1466 [inline]
 #0: ffffffff8c1a67f0 (dup_mmap_sem){.+.+}-{0:0}, at: copy_mm+0x21f/0x1380 kernel/fork.c:1518
 #1: ffff88807eb0a428 (&mm->mmap_lock){++++}-{3:3}, at: mmap_write_lock_killable include/linux/mmap_lock.h:87 [inline]
 #1: ffff88807eb0a428 (&mm->mmap_lock){++++}-{3:3}, at: dup_mmap kernel/fork.c:504 [inline]
 #1: ffff88807eb0a428 (&mm->mmap_lock){++++}-{3:3}, at: dup_mm kernel/fork.c:1466 [inline]
 #1: ffff88807eb0a428 (&mm->mmap_lock){++++}-{3:3}, at: copy_mm+0x238/0x1380 kernel/fork.c:1518
1 lock held by udevd/4498:
 #0: ffffffff8c1420f0 (cgroup_threadgroup_rwsem){++++}-{0:0}, at: do_exit+0x256/0x20a0 kernel/exit.c:830
2 locks held by syz-executor/4507:
 #0: ffffffff8c1a67f0 (dup_mmap_sem){.+.+}-{0:0}, at: dup_mmap kernel/fork.c:503 [inline]
 #0: ffffffff8c1a67f0 (dup_mmap_sem){.+.+}-{0:0}, at: dup_mm kernel/fork.c:1466 [inline]
 #0: ffffffff8c1a67f0 (dup_mmap_sem){.+.+}-{0:0}, at: copy_mm+0x21f/0x1380 kernel/fork.c:1518
 #1: ffff88807eb09d28 (&mm->mmap_lock){++++}-{3:3}, at: mmap_write_lock_killable include/linux/mmap_lock.h:87 [inline]
 #1: ffff88807eb09d28 (&mm->mmap_lock){++++}-{3:3}, at: dup_mmap kernel/fork.c:504 [inline]
 #1: ffff88807eb09d28 (&mm->mmap_lock){++++}-{3:3}, at: dup_mm kernel/fork.c:1466 [inline]
 #1: ffff88807eb09d28 (&mm->mmap_lock){++++}-{3:3}, at: copy_mm+0x238/0x1380 kernel/fork.c:1518
7 locks held by syz-executor/4509:
 #0: ffff888078ffe460 (sb_writers#11){.+.+}-{0:0}, at: vfs_write+0x28a/0xd00 fs/read_write.c:590
 #1: ffff88807eb38488 (&of->mutex){+.+.}-{3:3}, at: kernfs_fop_write_iter+0x1e5/0x4c0 fs/kernfs/file.c:287
 #2: ffffffff8c141f08 (cgroup_mutex){+.+.}-{3:3}, at: cgroup_kn_lock_live+0xee/0x230 kernel/cgroup/cgroup.c:1662
 #3: ffffffff8bfbadd0 (cpu_hotplug_lock){++++}-{0:0}, at: cgroup_attach_lock kernel/cgroup/cgroup.c:2411 [inline]
 #3: ffffffff8bfbadd0 (cpu_hotplug_lock){++++}-{0:0}, at: cgroup_procs_write_start+0x17c/0x580 kernel/cgroup/cgroup.c:2921
 #4: ffffffff8c1420f0 (cgroup_threadgroup_rwsem){++++}-{0:0}, at: cgroup_attach_lock kernel/cgroup/cgroup.c:2413 [inline]
 #4: ffffffff8c1420f0 (cgroup_threadgroup_rwsem){++++}-{0:0}, at: cgroup_procs_write_start+0x192/0x580 kernel/cgroup/cgroup.c:2921
 #5: ffffffff8c14fa48 (cpuset_mutex){+.+.}-{3:3}, at: cpuset_attach+0xac/0x5f0 kernel/cgroup/cpuset.c:2348
 #6: ffff88802b7b0f28 (&mm->mmap_lock){++++}-{3:3}, at: mmap_write_lock include/linux/mmap_lock.h:71 [inline]
 #6: ffff88802b7b0f28 (&mm->mmap_lock){++++}-{3:3}, at: mpol_rebind_mm+0x33/0x2c0 mm/mempolicy.c:381

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

NMI backtrace for cpu 0
CPU: 0 PID: 27 Comm: khungtaskd Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
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 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 PID: 3550 Comm: klogd Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
RIP: 0010:__orc_find arch/x86/kernel/unwind_orc.c:52 [inline]
RIP: 0010:orc_find arch/x86/kernel/unwind_orc.c:178 [inline]
RIP: 0010:unwind_next_frame+0x1073/0x1d90 arch/x86/kernel/unwind_orc.c:448
Code: 4c 89 f0 48 c1 e8 03 48 b9 00 00 00 00 00 fc ff df 0f b6 04 08 84 c0 75 27 49 63 06 4c 01 f0 49 8d 4e 04 48 39 e8 4c 0f 46 e9 <49> 8d 46 fc 4c 0f 47 e0 4d 0f 46 fe 4d 39 e5 76 a8 e9 be f1 ff ff
RSP: 0018:ffffc90002e2f328 EFLAGS: 00000206
RAX: ffffffff816678ed RBX: ffffc90002e2f3e8 RCX: ffffffff8d7a3e88
RDX: ffffffff8d7a3e58 RSI: ffffffff8de714e6 RDI: ffffffff8134790c
RBP: ffffffff816678b7 R08: 000000000000000f R09: 0000000000000000
R10: fffff520005c5e89 R11: 1ffff920005c5e87 R12: ffffffff8d7a3e90
R13: ffffffff8d7a3e78 R14: ffffffff8d7a3e84 R15: ffffffff8d7a3e74
FS:  00007fd508762c80(0000) GS:ffff8880b9100000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f4f51415000 CR3: 000000007df26000 CR4: 00000000003506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 arch_stack_walk+0x10c/0x140 arch/x86/kernel/stacktrace.c:25
 stack_trace_save+0x98/0xe0 kernel/stacktrace.c:122
 save_stack+0xf3/0x1e0 mm/page_owner.c:119
 __reset_page_owner+0x51/0x180 mm/page_owner.c:140
 reset_page_owner include/linux/page_owner.h:24 [inline]
 free_pages_prepare mm/page_alloc.c:1340 [inline]
 free_pcp_prepare mm/page_alloc.c:1391 [inline]
 free_unref_page_prepare+0x637/0x6c0 mm/page_alloc.c:3317
 free_unref_page+0x94/0x280 mm/page_alloc.c:3396
 free_slab mm/slub.c:2020 [inline]
 discard_slab mm/slub.c:2026 [inline]
 __unfreeze_partials+0x1a5/0x200 mm/slub.c:2512
 put_cpu_partial+0x12d/0x190 mm/slub.c:2592
 qlist_free_all+0x35/0x90 mm/kasan/quarantine.c:176
 kasan_quarantine_reduce+0x150/0x160 mm/kasan/quarantine.c:283
 ____kasan_kmalloc mm/kasan/common.c:479 [inline]
 __kasan_kmalloc+0x2f/0xf0 mm/kasan/common.c:522
 kmalloc include/linux/slab.h:604 [inline]
 syslog_print+0xd6/0x840 kernel/printk/printk.c:1500
 do_syslog+0x7f2/0x8f0 kernel/printk/printk.c:1679
 __do_sys_syslog kernel/printk/printk.c:1771 [inline]
 __se_sys_syslog kernel/printk/printk.c:1769 [inline]
 __x64_sys_syslog+0x78/0x90 kernel/printk/printk.c:1769
 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: 0033:0x7fd50892ca37
Code: 73 01 c3 48 8b 0d c1 f3 0c 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 b8 67 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 91 f3 0c 00 f7 d8 64 89 01 48
RSP: 002b:00007ffca214e7e8 EFLAGS: 00000206 ORIG_RAX: 0000000000000067
RAX: ffffffffffffffda RBX: 00007fd508acc490 RCX: 00007fd50892ca37
RDX: 00000000000003ff RSI: 00007fd508acc490 RDI: 0000000000000002
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000004000 R11: 0000000000000206 R12: 00007fd508acc490
R13: 00007fd508aa9dfe R14: 00007fd508acc617 R15: 00007fd508acc617
 </TASK>

Crashes (12):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/10/04 00:17 linux-5.15.y 29e53a5b1c4f 49379ee0 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan INFO: task hung in mpol_rebind_mm
2025/09/28 22:16 linux-5.15.y 43bb85222e53 001c9061 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf INFO: task hung in mpol_rebind_mm
2025/10/09 09:27 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 mpol_rebind_mm
2025/10/07 17:12 linux-5.15.y 29e53a5b1c4f 8ef35d49 .config console log report syz / log [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf INFO: task hung in mpol_rebind_mm
2025/10/31 18:38 linux-5.15.y cc5ec8769306 2c50b6a9 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf INFO: task hung in mpol_rebind_mm
2025/10/20 18:41 linux-5.15.y ac56c046adf4 d422939c .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan INFO: task hung in mpol_rebind_mm
2025/10/17 09:58 linux-5.15.y 29e53a5b1c4f 7adf5298 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf INFO: task hung in mpol_rebind_mm
2025/10/13 18:29 linux-5.15.y 29e53a5b1c4f b6605ba8 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan INFO: task hung in mpol_rebind_mm
2025/10/11 00:57 linux-5.15.y 29e53a5b1c4f ff1712fe .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf INFO: task hung in mpol_rebind_mm
2025/10/08 11:22 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 mpol_rebind_mm
2025/10/08 03:00 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 mpol_rebind_mm
2025/10/04 11:31 linux-5.15.y 29e53a5b1c4f 49379ee0 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf INFO: task hung in mpol_rebind_mm
* Struck through repros no longer work on HEAD.