syzbot


INFO: task hung in do_user_addr_fault

Status: upstream: reported C repro on 2025/10/04 15:08
Bug presence: origin:lts-only
[Documentation on labels]
Reported-by: syzbot+07cdd6021326bc8033cd@syzkaller.appspotmail.com
First crash: 57d, last: 17d
Bug presence (2)
Date Name Commit Repro Result
2025/10/04 linux-5.15.y (ToT) 29e53a5b1c4f C [report] no output from test machine
2025/10/04 upstream (ToT) cbf33b8e0b36 C Didn't crash
Similar bugs (3)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream INFO: task hung in do_user_addr_fault (3) ntfs3 1 C 32 988d 1063d 22/29 fixed on 2023/06/08 14:41
upstream INFO: task hung in do_user_addr_fault (2) kernel 1 C error error 5 1405d 1437d 0/29 closed as invalid on 2022/02/08 10:18
upstream INFO: task hung in do_user_addr_fault fs 1 1 1765d 1765d 0/29 auto-closed as invalid on 2021/05/17 11:48
Last patch testing requests (1)
Created Duration User Patch Repo Result
2025/10/22 14:59 18m retest repro linux-5.15.y OK log
Fix bisection attempts (1)
Created Duration User Patch Repo Result
2025/11/12 20:49 2h58m bisect fix linux-5.15.y OK (0) job log log

Sample crash report:
INFO: task syz-execprog:4228 blocked for more than 143 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz-execprog    state:D stack:25664 pid: 4228 ppid:  4219 flags:0x00004004
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
 rwsem_down_read_slowpath+0x528/0x990 kernel/locking/rwsem.c:1055
 __down_read_common kernel/locking/rwsem.c:1239 [inline]
 __down_read kernel/locking/rwsem.c:1252 [inline]
 down_read+0x96/0x2e0 kernel/locking/rwsem.c:1500
 mmap_read_lock+0x1c/0x50 include/linux/mmap_lock.h:117
 do_user_addr_fault+0xc35/0xc80 arch/x86/mm/fault.c:1308
 handle_page_fault arch/x86/mm/fault.c:1445 [inline]
 exc_page_fault+0x60/0x100 arch/x86/mm/fault.c:1501
 asm_exc_page_fault+0x22/0x30 arch/x86/include/asm/idtentry.h:606
RIP: 0033:0x427c87
RSP: 002b:000000c001b07e38 EFLAGS: 00010246
RAX: 000000c003020140 RBX: 000000c000fece10 RCX: 00000000000000a8
RDX: 00007f064c67b7e8 RSI: 000000c000065250 RDI: 00007f064c6cb560
RBP: 000000c001b07e70 R08: 000000000000000a R09: 0000000002033330
R10: 00000000000000a8 R11: 000000c003020140 R12: 0000000000000001
R13: 0000000000000001 R14: 000000c001517dc0 R15: 0000000000000001
 </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
2 locks held by udevd/3560:
 #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: ffff88807cb38128 (&mm->mmap_lock){++++}-{3:3}, at: mmap_write_lock_killable include/linux/mmap_lock.h:87 [inline]
 #1: ffff88807cb38128 (&mm->mmap_lock){++++}-{3:3}, at: dup_mmap kernel/fork.c:504 [inline]
 #1: ffff88807cb38128 (&mm->mmap_lock){++++}-{3:3}, at: dup_mm kernel/fork.c:1466 [inline]
 #1: ffff88807cb38128 (&mm->mmap_lock){++++}-{3:3}, at: copy_mm+0x238/0x1380 kernel/fork.c:1518
2 locks held by getty/3949:
 #0: ffff88814ce8d098 (&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 syz-execprog/4220:
 #0: ffff888079b8b228 (&mm->mmap_lock){++++}-{3:3}, at: mmap_write_lock_killable include/linux/mmap_lock.h:87 [inline]
 #0: ffff888079b8b228 (&mm->mmap_lock){++++}-{3:3}, at: vm_mmap_pgoff+0x15d/0x2b0 mm/util.c:549
1 lock held by syz-execprog/4228:
 #0: ffff888079b8b228 (&mm->mmap_lock){++++}-{3:3}, at: mmap_read_lock+0x1c/0x50 include/linux/mmap_lock.h:117
1 lock held by syz-executor/4229:
 #0: ffff88801edd7828 (&mm->mmap_lock){++++}-{3:3}, at: mmap_write_lock_killable include/linux/mmap_lock.h:87 [inline]
 #0: ffff88801edd7828 (&mm->mmap_lock){++++}-{3:3}, at: vm_mmap_pgoff+0x15d/0x2b0 mm/util.c:549
1 lock held by udevd/4348:
 #0: ffff88802b662b28 (&mm->mmap_lock){++++}-{3:3}, at: mmap_write_lock_killable include/linux/mmap_lock.h:87 [inline]
 #0: ffff88802b662b28 (&mm->mmap_lock){++++}-{3:3}, at: __vm_munmap+0xf3/0x230 mm/mmap.c:2949

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

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 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 1 to CPUs 0:
NMI backtrace for cpu 0 skipped: idling at native_safe_halt arch/x86/include/asm/irqflags.h:51 [inline]
NMI backtrace for cpu 0 skipped: idling at arch_safe_halt arch/x86/include/asm/irqflags.h:89 [inline]
NMI backtrace for cpu 0 skipped: idling at default_idle+0xb/0x10 arch/x86/kernel/process.c:729

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/10/04 15:07 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 do_user_addr_fault
2025/10/08 11:03 linux-5.15.y 29e53a5b1c4f 7e2882b3 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf INFO: task hung in do_user_addr_fault
* Struck through repros no longer work on HEAD.