[v6.6] INFO: task hung in fuse_flush

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: c56aaf1a85ae Linux 6.6.123
git tree: linux-6.6.y
console output: https://syzkaller.appspot.com/x/log.txt?x=11039b22580000
kernel config: https://syzkaller.appspot.com/x/.config?x=2a950bf7c0bff9f9
dashboard link: https://syzkaller.appspot.com/bug?extid=fce3ee7ecb9263019ca5
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/0c1480594070/disk-c56aaf1a.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/118e64c14227/vmlinux-c56aaf1a.xz
kernel image: https://storage.googleapis.com/syzbot-assets/320a7e9bfff1/bzImage-c56aaf1a.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+fce3ee...@syzkaller.appspotmail.com

INFO: task syz.0.10244:13188 blocked for more than 143 seconds.
Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.0.10244 state:D stack:27016 pid:13188 ppid:11697 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+0x55/0xa0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fb07039bf79
RSP: 002b:00007ffecaf71be8 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4
RAX: ffffffffffffffda RBX: 00007fb070617da0 RCX: 00007fb07039bf79
RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003
RBP: 00007fb070617da0 R08: 0000000000000006 R09: 0000000000000000
R10: 00007fb070617cb0 R11: 0000000000000246 R12: 000000000028478f
R13: 00007fb070615fac R14: 00000000002844e3 R15: 00007ffecaf71cf0
</TASK>
INFO: task syz.0.10244:13189 blocked for more than 143 seconds.
Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.0.10244 state:D stack:25352 pid:13189 ppid:11697 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
schedule_timeout+0xc1/0x2d0 kernel/time/timer.c:2144
do_wait_for_common kernel/sched/completion.c:95 [inline]
__wait_for_common kernel/sched/completion.c:116 [inline]
wait_for_common kernel/sched/completion.c:127 [inline]
wait_for_completion+0x2cb/0x5b0 kernel/sched/completion.c:148
fuse_direct_IO+0xa49/0x12b0 fs/fuse/file.c:3007
fuse_direct_write_iter fs/fuse/file.c:1642 [inline]
fuse_file_write_iter+0x8bd/0xf50 fs/fuse/file.c:1690
call_write_iter include/linux/fs.h:2018 [inline]
aio_write+0x564/0x7d0 fs/aio.c:1593
__io_submit_one fs/aio.c:-1 [inline]
io_submit_one+0x73f/0x12a0 fs/aio.c:2012
__do_sys_io_submit fs/aio.c:2071 [inline]
__se_sys_io_submit+0x1a1/0x310 fs/aio.c:2041
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x55/0xa0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fb07039bf79
RSP: 002b:00007fb0711e0028 EFLAGS: 00000246 ORIG_RAX: 00000000000000d1
RAX: ffffffffffffffda RBX: 00007fb070615fa0 RCX: 00007fb07039bf79
RDX: 0000200000000780 RSI: 0000000000000001 RDI: 00007fb071196000
RBP: 00007fb0704327e0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fb070616038 R14: 00007fb070615fa0 R15: 00007ffecaf71a88
</TASK>

Showing all locks held in the system:
1 lock held by khungtaskd/29:
#0: ffffffff8d131fe0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:334 [inline]
#0: ffffffff8d131fe0 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:786 [inline]
#0: ffffffff8d131fe0 (rcu_read_lock){....}-{1:2}, at: debug_show_all_locks+0x55/0x290 kernel/locking/lockdep.c:6633
2 locks held by kworker/u4:5/973:
2 locks held by getty/32128:
#0: ffff88814cce50a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:243
#1: ffffc900035652f0 (&ldata->atomic_read_lock){+.+.}-{3:3}, at: n_tty_read+0x433/0x1390 drivers/tty/n_tty.c:2217
1 lock held by syz.0.10244/13188:
#0: ffff88805f965fe0 (&sb->s_type->i_mutex_key#33){+.+.}-{3:3}, at: inode_lock include/linux/fs.h:804 [inline]
#0: ffff88805f965fe0 (&sb->s_type->i_mutex_key#33){+.+.}-{3:3}, at: fuse_flush+0x2ca/0x8b0 fs/fuse/file.c:527
1 lock held by syz.0.10244/13189:
#0: ffff88805f965fe0 (&sb->s_type->i_mutex_key#33){+.+.}-{3:3}, at: inode_lock include/linux/fs.h:804 [inline]
#0: ffff88805f965fe0 (&sb->s_type->i_mutex_key#33){+.+.}-{3:3}, at: fuse_direct_write_iter fs/fuse/file.c:-1 [inline]
#0: ffff88805f965fe0 (&sb->s_type->i_mutex_key#33){+.+.}-{3:3}, at: fuse_file_write_iter+0x6ab/0xf50 fs/fuse/file.c:1690

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

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 01/24/2026
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: 973 Comm: kworker/u4:5 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/24/2026
Workqueue: events_unbound nsim_dev_trap_report_work
RIP: 0010:__lock_acquire+0x1c12/0x7d40 kernel/locking/lockdep.c:5168
Code: 00 4a c7 44 00 10 00 00 00 00 42 c7 44 00 18 00 00 00 00 65 48 8b 04 25 28 00 00 00 48 3b 84 24 00 02 00 00 0f 85 8a 4c 00 00 <44> 89 f0 48 8d 65 d8 5b 41 5c 41 5d 41 5e 41 5f 5d c3 31 db e9 60
RSP: 0018:ffffc900041d71e0 EFLAGS: 00000046
RAX: 9c8d9192c8a8b100 RBX: ffff88802235a8d8 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000008 RDI: ffffffff911bf500
RBP: ffffc900041d7428 R08: dffffc0000000000 R09: 1ffffffff2237ea0
R10: dffffc0000000000 R11: fffffbfff2237ea1 R12: 8eb7da06293fd19f
R13: ffff888022359e00 R14: 0000000000000001 R15: ffff88802235a9a0
FS: 0000000000000000(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00005589226a4168 CR3: 000000000cf32000 CR4: 00000000003506f0
Call Trace:
<TASK>
lock_acquire+0x19e/0x420 kernel/locking/lockdep.c:5754
rcu_lock_acquire include/linux/rcupdate.h:334 [inline]
rcu_read_lock include/linux/rcupdate.h:786 [inline]
page_ext_get+0x3e/0x2b0 mm/page_ext.c:508
__page_table_check_zero+0x138/0x4b0 mm/page_table_check.c:148
prep_new_page mm/page_alloc.c:1588 [inline]
get_page_from_freelist+0x1951/0x19e0 mm/page_alloc.c:3220
__alloc_pages+0x1f0/0x460 mm/page_alloc.c:4486
alloc_slab_page+0x5d/0x160 mm/slub.c:1881
allocate_slab mm/slub.c:2028 [inline]
new_slab+0x87/0x2d0 mm/slub.c:2081
___slab_alloc+0xc5d/0x12f0 mm/slub.c:3253
__slab_alloc mm/slub.c:3339 [inline]
__slab_alloc_node mm/slub.c:3392 [inline]
slab_alloc_node mm/slub.c:3485 [inline]
__kmem_cache_alloc_node+0x19e/0x250 mm/slub.c:3534
__do_kmalloc_node mm/slab_common.c:1006 [inline]
__kmalloc_node_track_caller+0xa2/0x230 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:1284 [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+0x293/0xb00 drivers/net/netdevsim/dev.c:851
process_one_work kernel/workqueue.c:2634 [inline]
process_scheduled_works+0xa5d/0x15d0 kernel/workqueue.c:2711
worker_thread+0xa55/0xfc0 kernel/workqueue.c:2792
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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