[v6.6] INFO: task hung in fuse_flush (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 924b4a879cbb Linux 6.6.142
git tree: linux-6.6.y
console output: https://syzkaller.appspot.com/x/log.txt?x=16ec93b6580000
kernel config: https://syzkaller.appspot.com/x/.config?x=90249d2d52c08134
dashboard link: https://syzkaller.appspot.com/bug?extid=410fa69ca1fe8aa0b261
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/bd13425862f1/disk-924b4a87.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/eaa5de9e440b/vmlinux-924b4a87.xz
kernel image: https://storage.googleapis.com/syzbot-assets/5a9aa3293c15/bzImage-924b4a87.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+410fa6...@syzkaller.appspotmail.com

INFO: task syz.1.4551:21879 blocked for more than 143 seconds.
Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.1.4551 state:D stack:27016 pid:21879 ppid:14983 flags:0x00004006
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5381 [inline]
__schedule+0x1553/0x45a0 kernel/sched/core.c:6700
schedule+0xbd/0x170 kernel/sched/core.c:6774
schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:6833
rwsem_down_write_slowpath+0xc05/0xff0 kernel/locking/rwsem.c:1178
__down_write_common kernel/locking/rwsem.c:1306 [inline]
__down_write kernel/locking/rwsem.c:1315 [inline]
down_write+0x1b9/0x200 kernel/locking/rwsem.c:1574
inode_lock include/linux/fs.h:804 [inline]
fuse_flush+0x2ca/0x8b0 fs/fuse/file.c:527
filp_flush fs/open.c:1533 [inline]
filp_close+0xb1/0x150 fs/open.c:1546
__range_close fs/file.c:698 [inline]
__close_range+0x368/0x660 fs/file.c:755
__do_sys_close_range fs/open.c:1599 [inline]
__se_sys_close_range fs/open.c:1596 [inline]
__x64_sys_close_range+0x7a/0x90 fs/open.c:1596
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f6d46b9ce59
RSP: 002b:00007fff0a0dac98 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4
RAX: ffffffffffffffda RBX: 00007f6d46e17da0 RCX: 00007f6d46b9ce59
RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003
RBP: 00007f6d46e17da0 R08: 0000000000000006 R09: 0000000000000000
R10: 00007f6d46e17cb0 R11: 0000000000000246 R12: 00000000001dd8d7
R13: 00007f6d46e1609c R14: 00000000001dd659 R15: 00007f6d46e16090
</TASK>
INFO: task syz.1.4551:21880 blocked for more than 143 seconds.
Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.1.4551 state:D stack:26664 pid:21880 ppid:14983 flags:0x00004004
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5381 [inline]
__schedule+0x1553/0x45a0 kernel/sched/core.c:6700
schedule+0xbd/0x170 kernel/sched/core.c:6774
request_wait_answer fs/fuse/dev.c:407 [inline]
__fuse_request_send fs/fuse/dev.c:426 [inline]
fuse_simple_request+0x1204/0x1c70 fs/fuse/dev.c:513
fuse_send_write fs/fuse/file.c:1114 [inline]
fuse_direct_io+0x1e8b/0x2ac0 fs/fuse/file.c:1516
fuse_direct_IO+0x8f2/0x12b0 fs/fuse/file.c:2991
generic_file_direct_write+0x1d4/0x3e0 mm/filemap.c:3961
fuse_cache_write_iter fs/fuse/file.c:1369 [inline]
fuse_file_write_iter+0xb43/0xf50 fs/fuse/file.c:1688
call_write_iter include/linux/fs.h:2018 [inline]
new_sync_write fs/read_write.c:491 [inline]
vfs_write+0x46c/0x990 fs/read_write.c:584
ksys_write+0x150/0x260 fs/read_write.c:637
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f6d46b9ce59
RSP: 002b:00007f6d479b6028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f6d46e15fa0 RCX: 00007f6d46b9ce59
RDX: 0000000000001001 RSI: 00002000000001c0 RDI: 0000000000000005
RBP: 00007f6d46c32d6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f6d46e16038 R14: 00007f6d46e15fa0 R15: 00007fff0a0dab38
</TASK>

Showing all locks held in the system:
1 lock held by khungtaskd/29:
#0: ffffffff8d132160 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:334 [inline]
#0: ffffffff8d132160 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:786 [inline]
#0: ffffffff8d132160 (rcu_read_lock){....}-{1:2}, at: debug_show_all_locks+0x55/0x290 kernel/locking/lockdep.c:6633
2 locks held by kworker/1:2/1191:
2 locks held by getty/5534:
#0: ffff88802d35f0a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:243
#1: ffffc9000326e2f0 (&ldata->atomic_read_lock){+.+.}-{3:3}, at: n_tty_read+0x433/0x1390 drivers/tty/n_tty.c:2217
1 lock held by syz.1.4551/21879:
#0: ffff88805e340820 (&sb->s_type->i_mutex_key#21){+.+.}-{3:3}, at: inode_lock include/linux/fs.h:804 [inline]
#0: ffff88805e340820 (&sb->s_type->i_mutex_key#21){+.+.}-{3:3}, at: fuse_flush+0x2ca/0x8b0 fs/fuse/file.c:527
2 locks held by syz.1.4551/21880:
#0: ffff88802f2fe418 (sb_writers#14){.+.+}-{0:0}, at: vfs_write+0x21b/0x990 fs/read_write.c:580
#1: ffff88805e340820 (&sb->s_type->i_mutex_key#21){+.+.}-{3:3}, at: inode_lock include/linux/fs.h:804 [inline]
#1: ffff88805e340820 (&sb->s_type->i_mutex_key#21){+.+.}-{3:3}, at: fuse_cache_write_iter fs/fuse/file.c:1354 [inline]
#1: ffff88805e340820 (&sb->s_type->i_mutex_key#21){+.+.}-{3:3}, at: fuse_file_write_iter+0x2df/0xf50 fs/fuse/file.c:1688

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

NMI backtrace for cpu 1
CPU: 1 PID: 29 Comm: khungtaskd Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
Call Trace:
<TASK>
dump_stack_lvl+0x18c/0x250 lib/dump_stack.c:106
nmi_cpu_backtrace+0x3a6/0x3e0 lib/nmi_backtrace.c:113
nmi_trigger_cpumask_backtrace+0x17a/0x2f0 lib/nmi_backtrace.c:62
trigger_all_cpu_backtrace include/linux/nmi.h:160 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:222 [inline]
watchdog+0xf3d/0xf80 kernel/hung_task.c:379
kthread+0x2fa/0x390 kernel/kthread.c:388
ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293
</TASK>
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 7909 Comm: kworker/u4:13 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
Workqueue: events_unbound nsim_dev_trap_report_work
RIP: 0010:__read_once_word_nocheck+0x0/0x10 include/asm-generic/rwonce.h:66
Code: df e8 a4 fd a3 00 e9 a0 fd ff ff 44 89 e1 80 e1 07 38 c1 0f 8c 5d fc ff ff 4c 89 e7 e8 e9 fd a3 00 e9 50 fc ff ff 0f 1f 40 00 <53> 48 89 fb e8 77 bd 4b 00 48 8b 03 5b c3 cc cc f3 0f 1e fa 55 48
RSP: 0018:ffffc90004b1f510 EFLAGS: 00000293
RAX: ffffffff813b64b7 RBX: 1ffff92000963ec9 RCX: ffff88807a92da00
RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffffc90004b1f780
RBP: ffffc90004b1f780 R08: ffff88807a92da00 R09: 0000000000000003
R10: 0000000000000004 R11: 0000000000000000 R12: ffffc90004b20000
R13: 1ffff92000963ecb R14: ffffc90004b18000 R15: dffffc0000000000
FS: 0000000000000000(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055969844bc70 CR3: 000000002fb39000 CR4: 00000000003506f0
Call Trace:
<TASK>
deref_stack_reg+0x1bd/0x240 arch/x86/kernel/unwind_orc.c:406
unwind_next_frame+0x1789/0x2970 arch/x86/kernel/unwind_orc.c:648
arch_stack_walk+0x144/0x190 arch/x86/kernel/stacktrace.c:25
stack_trace_save+0xaa/0x100 kernel/stacktrace.c:122
kasan_save_stack mm/kasan/common.c:46 [inline]
kasan_set_track+0x4e/0x70 mm/kasan/common.c:53
____kasan_kmalloc mm/kasan/common.c:375 [inline]
__kasan_kmalloc+0x8f/0xa0 mm/kasan/common.c:384
kasan_kmalloc include/linux/kasan.h:198 [inline]
__do_kmalloc_node mm/slab_common.c:1007 [inline]
__kmalloc_node_track_caller+0xb2/0x230 mm/slab_common.c:1027
kmalloc_reserve+0x116/0x240 net/core/skbuff.c:584
__alloc_skb+0x138/0x2c0 net/core/skbuff.c:653
alloc_skb include/linux/skbuff.h:1316 [inline]
nsim_dev_trap_skb_build drivers/net/netdevsim/dev.c:748 [inline]
nsim_dev_trap_report drivers/net/netdevsim/dev.c:805 [inline]
nsim_dev_trap_report_work+0x293/0xb10 drivers/net/netdevsim/dev.c:851
process_one_work kernel/workqueue.c:2653 [inline]
process_scheduled_works+0xa5d/0x15d0 kernel/workqueue.c:2730
worker_thread+0xa55/0xfc0 kernel/workqueue.c:2811
kthread+0x2fa/0x390 kernel/kthread.c:388
ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293
</TASK>


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