Re: [syzbot] [ntfs3?] INFO: task hung in __start_renaming

Mateusz Guzik
2025-11-24T06:29:07Z

On Sun, Nov 23, 2025 at 02:44:29PM -0800, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: fe4d0dea039f Add linux-next specific files for 20251119
> git tree: linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=142c0514580000
> kernel config: https://syzkaller.appspot.com/x/.config?x=f20a6db7594dcad7
> dashboard link: https://syzkaller.appspot.com/bug?extid=2fefb910d2c20c0698d8
> compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=11cd7692580000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=17615658580000
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/ce4f26d91a01/disk-fe4d0dea.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/6c9b53acf521/vmlinux-fe4d0dea.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/64d37d01cd64/bzImage-fe4d0dea.xz
> mounted in repro: https://storage.googleapis.com/syzbot-assets/a91529a880b1/mount_0.gz
>
> The issue was bisected to:
>
> commit 1e3c3784221ac86401aea72e2bae36057062fc9c
> Author: Mateusz Guzik <mjguzik@gmail.com>
> Date: Fri Oct 10 22:17:36 2025 +0000
>
> fs: rework I_NEW handling to operate without fences
>
> bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=17739742580000
> final oops: https://syzkaller.appspot.com/x/report.txt?x=14f39742580000
> console output: https://syzkaller.appspot.com/x/log.txt?x=10f39742580000
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+2fefb910d2c20c0698d8@syzkaller.appspotmail.com
> Fixes: 1e3c3784221a ("fs: rework I_NEW handling to operate without fences")
>
> INFO: task syz.0.17:6022 blocked for more than 143 seconds.
> Not tainted syzkaller #0
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> task:syz.0.17 state:D stack:28744 pid:6022 tgid:6020 ppid:5945 task_flags:0x400040 flags:0x00080002
> Call Trace:
> <TASK>
> context_switch kernel/sched/core.c:5263 [inline]
> __schedule+0x1836/0x4ed0 kernel/sched/core.c:6871
> __schedule_loop kernel/sched/core.c:6953 [inline]
> schedule+0x165/0x360 kernel/sched/core.c:6968
> schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:7025
> rwsem_down_write_slowpath+0x872/0xfe0 kernel/locking/rwsem.c:1185
> __down_write_common kernel/locking/rwsem.c:1317 [inline]
> __down_write kernel/locking/rwsem.c:1326 [inline]
> down_write_nested+0x1b5/0x200 kernel/locking/rwsem.c:1707
> inode_lock_nested include/linux/fs.h:1072 [inline]
> lock_rename fs/namei.c:3681 [inline]
> __start_renaming+0x148/0x410 fs/namei.c:3777
> do_renameat2+0x399/0x8e0 fs/namei.c:5991
> __do_sys_rename fs/namei.c:6059 [inline]
> __se_sys_rename fs/namei.c:6057 [inline]
> __x64_sys_rename+0x82/0x90 fs/namei.c:6057
> do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
> do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
> entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f7ba9b8f749
> RSP: 002b:00007f7ba91dd038 EFLAGS: 00000246 ORIG_RAX: 0000000000000052
> RAX: ffffffffffffffda RBX: 00007f7ba9de6090 RCX: 00007f7ba9b8f749
> RDX: 0000000000000000 RSI: 0000200000000080 RDI: 0000200000000340
> RBP: 00007f7ba9c13f91 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007f7ba9de6128 R14: 00007f7ba9de6090 R15: 00007fff2ce8d188
> </TASK>
>
> Showing all locks held in the system:
> 1 lock held by khungtaskd/31:
> #0: ffffffff8df3d740 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
> #0: ffffffff8df3d740 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:867 [inline]
> #0: ffffffff8df3d740 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x2e/0x180 kernel/locking/lockdep.c:6775
> 2 locks held by getty/5589:
> #0: ffff88814d56c0a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:243
> #1: ffffc9000332b2f0 (&ldata->atomic_read_lock){+.+.}-{4:4}, at: n_tty_read+0x43e/0x1400 drivers/tty/n_tty.c:2222
> 3 locks held by syz.0.17/6021:
> 2 locks held by syz.0.17/6022:
> #0: ffff888030718420 (sb_writers#12){.+.+}-{0:0}, at: mnt_want_write+0x41/0x90 fs/namespace.c:509
> #1: ffff8880631e3dd8 (&type->i_mutex_dir_key#8/1){+.+.}-{4:4}, at: inode_lock_nested include/linux/fs.h:1072 [inline]
> #1: ffff8880631e3dd8 (&type->i_mutex_dir_key#8/1){+.+.}-{4:4}, at: lock_rename fs/namei.c:3681 [inline]
> #1: ffff8880631e3dd8 (&type->i_mutex_dir_key#8/1){+.+.}-{4:4}, at: __start_renaming+0x148/0x410 fs/namei.c:3777
> 3 locks held by syz.1.18/6048:
> 2 locks held by syz.1.18/6049:
> #0: ffff888077cbe420 (sb_writers#12){.+.+}-{0:0}, at: mnt_want_write+0x41/0x90 fs/namespace.c:509
> #1: ffff8880632db690 (&type->i_mutex_dir_key#8/1){+.+.}-{4:4}, at: inode_lock_nested include/linux/fs.h:1072 [inline]
> #1: ffff8880632db690 (&type->i_mutex_dir_key#8/1){+.+.}-{4:4}, at: lock_rename fs/namei.c:3681 [inline]
> #1: ffff8880632db690 (&type->i_mutex_dir_key#8/1){+.+.}-{4:4}, at: __start_renaming+0x148/0x410 fs/namei.c:3777
> 3 locks held by syz.2.19/6082:
> 2 locks held by syz.2.19/6083:
> #0: ffff88807945e420 (sb_writers#12){.+.+}-{0:0}, at: mnt_want_write+0x41/0x90 fs/namespace.c:509
> #1: ffff888073281970 (&type->i_mutex_dir_key#8/1){+.+.}-{4:4}, at: inode_lock_nested include/linux/fs.h:1072 [inline]
> #1: ffff888073281970 (&type->i_mutex_dir_key#8/1){+.+.}-{4:4}, at: lock_rename fs/namei.c:3681 [inline]
> #1: ffff888073281970 (&type->i_mutex_dir_key#8/1){+.+.}-{4:4}, at: __start_renaming+0x148/0x410 fs/namei.c:3777
> 3 locks held by syz.3.20/6107:
> 2 locks held by syz.3.20/6108:
> #0: ffff88807b0a4420 (sb_writers#12){.+.+}-{0:0}, at: mnt_want_write+0x41/0x90 fs/namespace.c:509
> #1: ffff8880631e1228 (&type->i_mutex_dir_key#8/1){+.+.}-{4:4}, at: inode_lock_nested include/linux/fs.h:1072 [inline]
> #1: ffff8880631e1228 (&type->i_mutex_dir_key#8/1){+.+.}-{4:4}, at: lock_rename fs/namei.c:3681 [inline]
> #1: ffff8880631e1228 (&type->i_mutex_dir_key#8/1){+.+.}-{4:4}, at: __start_renaming+0x148/0x410 fs/namei.c:3777
> 3 locks held by syz.4.21/6138:
> 2 locks held by syz.4.21/6139:
> #0: ffff8880587fe420 (sb_writers#12){.+.+}-{0:0}, at: mnt_want_write+0x41/0x90 fs/namespace.c:509
> #1: ffff8880632d8ae0 (&type->i_mutex_dir_key#8/1){+.+.}-{4:4}, at: inode_lock_nested include/linux/fs.h:1072 [inline]
> #1: ffff8880632d8ae0 (&type->i_mutex_dir_key#8/1){+.+.}-{4:4}, at: lock_rename fs/namei.c:3681 [inline]
> #1: ffff8880632d8ae0 (&type->i_mutex_dir_key#8/1){+.+.}-{4:4}, at: __start_renaming+0x148/0x410 fs/namei.c:3777
> 3 locks held by syz.5.22/6176:
> 2 locks held by syz.5.22/6177:
> #0: ffff888026cec420 (sb_writers#12){.+.+}-{0:0}, at: mnt_want_write+0x41/0x90 fs/namespace.c:509
> #1: ffff8880631ce240 (&type->i_mutex_dir_key#8/1){+.+.}-{4:4}, at: inode_lock_nested include/linux/fs.h:1072 [inline]
> #1: ffff8880631ce240 (&type->i_mutex_dir_key#8/1){+.+.}-{4:4}, at: lock_rename fs/namei.c:3681 [inline]
> #1: ffff8880631ce240 (&type->i_mutex_dir_key#8/1){+.+.}-{4:4}, at: __start_renaming+0x148/0x410 fs/namei.c:3777
> 3 locks held by syz.6.23/6211:
> 2 locks held by syz.6.23/6212:
> #0: ffff888027d88420 (sb_writers#12){.+.+}-{0:0}, at: mnt_want_write+0x41/0x90 fs/namespace.c:509
> #1: ffff8880631c9228 (&type->i_mutex_dir_key#8/1){+.+.}-{4:4}, at: inode_lock_nested include/linux/fs.h:1072 [inline]
> #1: ffff8880631c9228 (&type->i_mutex_dir_key#8/1){+.+.}-{4:4}, at: lock_rename fs/namei.c:3681 [inline]
> #1: ffff8880631c9228 (&type->i_mutex_dir_key#8/1){+.+.}-{4:4}, at: __start_renaming+0x148/0x410 fs/namei.c:3777
> 3 locks held by syz.7.24/6244:
> 2 locks held by syz.7.24/6245:
> #0: ffff88807d516420 (sb_writers#12){.+.+}-{0:0}, at: mnt_want_write+0x41/0x90 fs/namespace.c:509
> #1: ffff8880631bdaf8 (&type->i_mutex_dir_key#8/1){+.+.}-{4:4}, at: inode_lock_nested include/linux/fs.h:1072 [inline]
> #1: ffff8880631bdaf8 (&type->i_mutex_dir_key#8/1){+.+.}-{4:4}, at: lock_rename fs/namei.c:3681 [inline]
> #1: ffff8880631bdaf8 (&type->i_mutex_dir_key#8/1){+.+.}-{4:4}, at: __start_renaming+0x148/0x410 fs/namei.c:3777
>
> =============================================
>
> NMI backtrace for cpu 0
> CPU: 0 UID: 0 PID: 31 Comm: khungtaskd Not tainted syzkaller #0 PREEMPT(full)
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
> Call Trace:
> <TASK>
> dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
> nmi_cpu_backtrace+0x39e/0x3d0 lib/nmi_backtrace.c:113
> nmi_trigger_cpumask_backtrace+0x17a/0x300 lib/nmi_backtrace.c:62
> trigger_all_cpu_backtrace include/linux/nmi.h:160 [inline]
> __sys_info lib/sys_info.c:157 [inline]
> sys_info+0x135/0x170 lib/sys_info.c:165
> check_hung_uninterruptible_tasks kernel/hung_task.c:346 [inline]
> watchdog+0xfb5/0x1000 kernel/hung_task.c:515
> kthread+0x711/0x8a0 kernel/kthread.c:463
> ret_from_fork+0x599/0xb30 arch/x86/kernel/process.c:158
> ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
> </TASK>
> Sending NMI from CPU 0 to CPUs 1:
> NMI backtrace for cpu 1
> CPU: 1 UID: 0 PID: 6107 Comm: syz.3.20 Not tainted syzkaller #0 PREEMPT(full)
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
> RIP: 0010:hlock_class kernel/locking/lockdep.c:234 [inline]
> RIP: 0010:mark_lock+0x3c/0x190 kernel/locking/lockdep.c:4731
> Code: 00 03 00 83 f9 01 bb 09 00 00 00 83 db 00 83 fa 08 0f 45 da bd 01 00 00 00 89 d9 d3 e5 25 ff 1f 00 00 48 0f a3 05 c4 46 df 11 <73> 10 48 69 c0 c8 00 00 00 48 8d 88 70 f3 1e 93 eb 48 83 3d 4b d6
> RSP: 0018:ffffc90003747518 EFLAGS: 00000007
> RAX: 0000000000000311 RBX: 0000000000000008 RCX: 0000000000000008
> RDX: 0000000000000008 RSI: ffff8880275f48a8 RDI: ffff8880275f3d00
> RBP: 0000000000000100 R08: 0000000000000000 R09: ffffffff8241cc56
> R10: dffffc0000000000 R11: ffffed100e650518 R12: 0000000000000004
> R13: 0000000000000003 R14: ffff8880275f48a8 R15: 0000000000000000
> FS: 00007fc3607da6c0(0000) GS:ffff888125fbc000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000558e8c347168 CR3: 0000000077b26000 CR4: 00000000003526f0
> Call Trace:
> <TASK>
> mark_usage kernel/locking/lockdep.c:4674 [inline]
> __lock_acquire+0x6a8/0xd20 kernel/locking/lockdep.c:5191
> lock_acquire+0x117/0x350 kernel/locking/lockdep.c:5868
> __raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline]
> _raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:154
> spin_lock include/linux/spinlock.h:351 [inline]
> insert_inode_locked+0x336/0x5d0 fs/inode.c:1837
> ntfs_new_inode+0xc8/0x100 fs/ntfs3/fsntfs.c:1675
> ntfs_create_inode+0x606/0x32a0 fs/ntfs3/inode.c:1309
> ntfs_create+0x3d/0x50 fs/ntfs3/namei.c:110
> lookup_open fs/namei.c:4409 [inline]
> open_last_lookups fs/namei.c:4509 [inline]
> path_openat+0x190f/0x3d90 fs/namei.c:4753
> do_filp_open+0x1fa/0x410 fs/namei.c:4783
> do_sys_openat2+0x121/0x1c0 fs/open.c:1432
> do_sys_open fs/open.c:1447 [inline]
> __do_sys_openat fs/open.c:1463 [inline]
> __se_sys_openat fs/open.c:1458 [inline]
> __x64_sys_openat+0x138/0x170 fs/open.c:1458
> do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
> do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
> entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7fc35f98f749
> Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007fc3607da038 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
> RAX: ffffffffffffffda RBX: 00007fc35fbe5fa0 RCX: 00007fc35f98f749
> RDX: 000000000000275a RSI: 00002000000001c0 RDI: ffffffffffffff9c
> RBP: 00007fc35fa13f91 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007fc35fbe6038 R14: 00007fc35fbe5fa0 R15: 00007ffffeb34448
> </TASK>
>
>

#syz test

index a62032864ddf..7f4c74cc09b5 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -1057,6 +1057,7 @@ static struct inode *find_inode(struct super_block *sb,
__wait_on_freeing_inode(inode, is_inode_hash_locked);
goto repeat;
}
+ BUG_ON(inode_unhashed(inode));
if (unlikely(inode_state_read(inode) & I_CREATING)) {
spin_unlock(&inode->i_lock);
rcu_read_unlock();
@@ -1099,6 +1100,7 @@ static struct inode *find_inode_fast(struct super_block *sb,
__wait_on_freeing_inode(inode, is_inode_hash_locked);
goto repeat;
}
+ BUG_ON(inode_unhashed(inode));
if (unlikely(inode_state_read(inode) & I_CREATING)) {
spin_unlock(&inode->i_lock);
rcu_read_unlock();
@@ -1318,6 +1320,8 @@ struct inode *inode_insert5(struct inode *inode, unsigned long hashval,
iput(old);
goto again;
}
+ } else {
+ BUG_ON(inode_unhashed(old));
}
return old;
}
@@ -1420,6 +1424,8 @@ struct inode *iget5_locked_rcu(struct super_block *sb, unsigned long hashval,
iput(inode);
goto again;
}
+ } else {
+ BUG_ON(inode_unhashed(inode));
}
return inode;
}
@@ -1466,6 +1472,8 @@ struct inode *iget_locked(struct super_block *sb, unsigned long ino)
iput(inode);
goto again;
}
+ } else {
+ BUG_ON(inode_unhashed(inode));
}
return inode;
}
@@ -1508,6 +1516,8 @@ struct inode *iget_locked(struct super_block *sb, unsigned long ino)
iput(inode);
goto again;
}
+ } else {
+ BUG_ON(inode_unhashed(inode));
}
}
return inode;
@@ -1655,6 +1665,8 @@ struct inode *ilookup5(struct super_block *sb, unsigned long hashval,
iput(inode);
goto again;
}
+ } else {
+ BUG_ON(inode_unhashed(inode));
}
}
return inode;
@@ -1689,6 +1701,8 @@ struct inode *ilookup(struct super_block *sb, unsigned long ino)
iput(inode);
goto again;
}
+ } else {
+ BUG_ON(inode_unhashed(inode));
}
}
return inode;
@@ -1855,6 +1869,7 @@ int insert_inode_locked(struct inode *inode)
spin_unlock(&inode_hash_lock);
return 0;
}
+ BUG_ON(inode_unhashed(old));
if (unlikely(inode_state_read(old) & I_CREATING)) {
spin_unlock(&old->i_lock);
spin_unlock(&inode_hash_lock);
@@ -1870,6 +1885,8 @@ int insert_inode_locked(struct inode *inode)
iput(old);
return -EBUSY;
}
+ } else {
+ BUG_ON(inode_unhashed(old));
}
iput(old);
}