syzbot


INFO: task hung in fuse_simple_request (4)

Status: upstream: reported on 2025/10/25 20:54
Reported-by: syzbot+cd83f334cffc0e28ef31@syzkaller.appspotmail.com
First crash: 47d, last: 7d10h
Similar bugs (9)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-6.6 INFO: task hung in fuse_simple_request (2) 1 2 7d09h 47d 0/2 upstream: reported on 2025/10/25 20:31
linux-5.15 INFO: task hung in fuse_simple_request (2) 1 3 418d 536d 0/3 auto-obsoleted due to no activity on 2025/01/28 01:40
linux-5.15 INFO: task hung in fuse_simple_request 1 12 778d 876d 0/3 auto-obsoleted due to no activity on 2024/02/03 13:59
linux-6.6 INFO: task hung in fuse_simple_request 1 1 150d 150d 0/2 auto-obsoleted due to no activity on 2025/10/23 13:22
upstream INFO: task hung in fuse_simple_request fuse 1 C inconclusive error 273 445d 1824d 0/29 upstream: reported C repro on 2020/12/13 21:13
linux-6.1 INFO: task hung in fuse_simple_request 1 6 755d 843d 0/3 auto-obsoleted due to no activity on 2024/02/26 14:29
linux-5.15 INFO: task hung in fuse_simple_request (3) 1 9 172d 286d 0/3 auto-obsoleted due to no activity on 2025/09/30 15:49
linux-6.1 INFO: task hung in fuse_simple_request (2) origin:upstream 1 syz 26 7d09h 538d 0/3 upstream: reported syz repro on 2024/06/21 20:45
upstream INFO: task can't die in request_wait_answer fuse 1 C error 14 1395d 1906d 0/29 auto-obsoleted due to no activity on 2023/04/16 22:02

Sample crash report:
INFO: task syz.2.101:4612 blocked for more than 143 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.2.101       state:D stack:26928 pid: 4612 ppid:  4188 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
 request_wait_answer fs/fuse/dev.c:411 [inline]
 __fuse_request_send fs/fuse/dev.c:430 [inline]
 fuse_simple_request+0x10e7/0x19c0 fs/fuse/dev.c:515
 fuse_lookup_name+0x279/0x700 fs/fuse/dir.c:383
 fuse_lookup+0x13b/0x5a0 fs/fuse/dir.c:428
 __lookup_slow+0x27d/0x3d0 fs/namei.c:1671
 lookup_slow+0x53/0x70 fs/namei.c:1688
 walk_component+0x319/0x460 fs/namei.c:1984
 lookup_last fs/namei.c:2439 [inline]
 path_lookupat+0x169/0x440 fs/namei.c:2463
 filename_lookup+0x1e2/0x4f0 fs/namei.c:2492
 user_path_at_empty+0x40/0x190 fs/namei.c:2891
 user_path_at include/linux/namei.h:57 [inline]
 vfs_statx+0x102/0x4d0 fs/stat.c:221
 vfs_fstatat fs/stat.c:243 [inline]
 __do_sys_newfstatat fs/stat.c:411 [inline]
 __se_sys_newfstatat fs/stat.c:405 [inline]
 __x64_sys_newfstatat+0x12c/0x1b0 fs/stat.c:405
 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: 0033:0x7f733c073749
RSP: 002b:00007f733a2da038 EFLAGS: 00000246 ORIG_RAX: 0000000000000106
RAX: ffffffffffffffda RBX: 00007f733c2c9fa0 RCX: 00007f733c073749
RDX: 00002000000009c0 RSI: 0000200000000880 RDI: ffffffffffffff9c
RBP: 00007f733c0f7f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000004000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f733c2ca038 R14: 00007f733c2c9fa0 R15: 00007ffe15b38b68
 </TASK>

Showing all locks held in the system:
2 locks held by ksoftirqd/0/14:
1 lock held by khungtaskd/27:
 #0: ffffffff8c11c760 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x0/0x30
2 locks held by getty/3947:
 #0: ffff88802bb54098 (&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
2 locks held by syz.2.101/4612:
 #0: ffff888061f00ed0 (&type->i_mutex_dir_key#14){.+.+}-{3:3}, at: inode_lock_shared include/linux/fs.h:797 [inline]
 #0: ffff888061f00ed0 (&type->i_mutex_dir_key#14){.+.+}-{3:3}, at: lookup_slow+0x46/0x70 fs/namei.c:1687
 #1: ffff888061f01338 (&fi->mutex){+.+.}-{3:3}, at: fuse_lock_inode+0xcd/0x120 fs/fuse/inode.c:491
2 locks held by kworker/1:9/5520:
 #0: ffff888016872138 ((wq_completion)rcu_gp){+.+.}-{0:0}, at: process_one_work+0x760/0x1000 kernel/workqueue.c:-1
 #1: ffffc900030efd00 ((work_completion)(&rew.rew_work)){+.+.}-{0:0}, at: process_one_work+0x7a3/0x1000 kernel/workqueue.c:2285
2 locks held by syz-executor/6427:
 #0: ffff8880201d2118 (&disk->open_mutex){+.+.}-{3:3}, at: blkdev_put+0xf9/0x7d0 block/bdev.c:915
 #1: ffff888147812468 (&lo->lo_mutex){+.+.}-{3:3}, at: lo_release+0x4d/0x1f0 drivers/block/loop.c:2071
1 lock held by syz-executor/7362:
 #0: ffffffff8c1211e8 (rcu_state.exp_mutex){+.+.}-{3:3}, at: exp_funnel_lock kernel/rcu/tree_exp.h:290 [inline]
 #0: ffffffff8c1211e8 (rcu_state.exp_mutex){+.+.}-{3:3}, at: synchronize_rcu_expedited+0x347/0x6b0 kernel/rcu/tree_exp.h:845

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

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: 4308 Comm: kworker/0:9 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Workqueue: events nsim_dev_trap_report_work
RIP: 0010:check_wait_context kernel/locking/lockdep.c:4700 [inline]
RIP: 0010:__lock_acquire+0x6b5/0x7c60 kernel/locking/lockdep.c:4962
Code: 69 63 00 00 45 8b bd e8 0a 00 00 41 8d 47 ff 83 f8 ff 41 bc ff ff ff ff 44 0f 4c e0 49 81 c5 10 0b 00 00 41 ff c4 45 8d 77 01 <49> ff cf 44 89 f0 83 c0 fe 0f 88 70 01 00 00 44 89 fb 81 e3 ff ff
RSP: 0018:ffffc900034ff5e0 EFLAGS: 00000056
RAX: 0000000000000001 RBX: 0000000000000000 RCX: 0000000000000003
RDX: 0000000000000000 RSI: 0000000000000008 RDI: ffffffff8ffbe1b8
RBP: ffffc900034ff830 R08: dffffc0000000000 R09: fffffbfff1ff7c38
R10: fffffbfff1ff7c38 R11: 1ffffffff1ff7c37 R12: 0000000000000000
R13: ffff888025bec690 R14: 0000000000000003 R15: 0000000000000002
FS:  0000000000000000(0000) GS:ffff8880b9000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007efc23a63440 CR3: 00000000768f5000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 lock_acquire+0x197/0x3f0 kernel/locking/lockdep.c:5623
 __mutex_lock_common+0x1eb/0x2390 kernel/locking/mutex.c:596
 __mutex_lock kernel/locking/mutex.c:729 [inline]
 mutex_lock_nested+0x17/0x20 kernel/locking/mutex.c:743
 nsim_dev_trap_report_work+0x56/0xb40 drivers/net/netdevsim/dev.c:757
 process_one_work+0x863/0x1000 kernel/workqueue.c:2310
 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 (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/12/05 05:04 linux-5.15.y cc5ec8769306 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan INFO: task hung in fuse_simple_request
2025/10/25 20:54 linux-5.15.y ac56c046adf4 c0460fcd .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan INFO: task hung in fuse_simple_request
* Struck through repros no longer work on HEAD.