[syzbot] [nilfs?] INFO: task hung in nilfs_segctor_thread (6)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 8f0b4cce4481 Linux 6.19-rc1
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=178ac11a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=1f2b6fe1fdf1a00b
dashboard link: https://syzkaller.appspot.com/bug?extid=7eedce5eb281acd832f0
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=12efdb90580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=10f9cd92580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/ea3b19e4d883/disk-8f0b4cce.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/bd7c115820ba/vmlinux-8f0b4cce.xz
kernel image: https://storage.googleapis.com/syzbot-assets/e5813cc1963f/bzImage-8f0b4cce.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/80eb4ac785e9/mount_0.gz

The issue was bisected to:

commit 2b9ac22b12a266eb4fec246a07b504dd4983b16b
Author: Kristian Klausen <kris...@klausen.dk>
Date: Fri Jun 18 11:51:57 2021 +0000

loop: Fix missing discard support when using LOOP_CONFIGURE

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=17e3b11a580000
final oops: https://syzkaller.appspot.com/x/report.txt?x=1413b11a580000
console output: https://syzkaller.appspot.com/x/log.txt?x=1013b11a580000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+7eedce...@syzkaller.appspotmail.com
Fixes: 2b9ac22b12a2 ("loop: Fix missing discard support when using LOOP_CONFIGURE")

INFO: tas[ 327.531540][ T38] INFO: task segctord:6093 blocked for more than 143 seconds.
Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:segctord state:D stack:28968 pid:6093 tgid:6093 ppid:2 task_flags:0x200040 flags:0x00080000
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5256 [inline]
__schedule+0x1480/0x50a0 kernel/sched/core.c:6863
__schedule_loop kernel/sched/core.c:6945 [inline]
rt_mutex_schedule+0x77/0xf0 kernel/sched/core.c:7241
rwbase_write_lock+0x3dd/0x750 kernel/locking/rwbase_rt.c:272
nilfs_transaction_lock+0x253/0x4c0 fs/nilfs2/segment.c:357
nilfs_segctor_thread_construct fs/nilfs2/segment.c:2569 [inline]
nilfs_segctor_thread+0x6ec/0xe00 fs/nilfs2/segment.c:2684
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>

Showing all locks held in the system:
1 lock held by khungtaskd/38:
#0: ffffffff8d5ae880 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
#0: ffffffff8d5ae880 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:867 [inline]
#0: ffffffff8d5ae880 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x2e/0x180 kernel/locking/lockdep.c:6775
3 locks held by kworker/u8:14/1555:
2 locks held by getty/5561:
#0: ffff8880354c00a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:243
#1: ffffc90003e8b2e0 (&ldata->atomic_read_lock){+.+.}-{4:4}, at: n_tty_read+0x44f/0x1460 drivers/tty/n_tty.c:2211
1 lock held by syz-executor/5830:
5 locks held by syz.0.17/6090:
1 lock held by segctord/6093:
#0: ffff88803672b2b0 (&nilfs->ns_segctor_sem){++++}-{4:4}, at: nilfs_transaction_lock+0x253/0x4c0 fs/nilfs2/segment.c:357
2 locks held by syz.1.18/6168:
1 lock held by segctord/6169:
#0: ffff88805c1e12b0 (&nilfs->ns_segctor_sem){++++}-{4:4}, at: nilfs_transaction_lock+0x253/0x4c0 fs/nilfs2/segment.c:357
2 locks held by syz.2.19/6194:
1 lock held by segctord/6195:
#0: ffff88801fadf2b0 (&nilfs->ns_segctor_sem){++++}-{4:4}, at: nilfs_transaction_lock+0x253/0x4c0 fs/nilfs2/segment.c:357
3 locks held by syz.3.20/6222:
1 lock held by segctord/6223:
#0: ffff88801b7aa2b0 (&nilfs->ns_segctor_sem){++++}-{4:4}, at: nilfs_transaction_lock+0x253/0x4c0 fs/nilfs2/segment.c:357
4 locks held by syz.4.21/6261:
1 lock held by segctord/6263:
#0: ffff8880308212b0 (&nilfs->ns_segctor_sem){++++}-{4:4}, at: nilfs_transaction_lock+0x253/0x4c0 fs/nilfs2/segment.c:357
3 locks held by syz.5.22/6295:
1 lock held by segctord/6296:
#0: ffff888033ee82b0 (&nilfs->ns_segctor_sem){++++}-{4:4}, at: nilfs_transaction_lock+0x253/0x4c0 fs/nilfs2/segment.c:357
2 locks held by syz.6.23/6334:
1 lock held by segctord/6335:
#0: ffff888038fc92b0 (&nilfs->ns_segctor_sem){++++}-{4:4}, at: nilfs_transaction_lock+0x253/0x4c0 fs/nilfs2/segment.c:357

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

NMI backtrace for cpu 1
CPU: 1 UID: 0 PID: 38 Comm: khungtaskd Not tainted syzkaller #0 PREEMPT_{RT,(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+0xf95/0xfe0 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 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 6295 Comm: syz.5.22 Not tainted syzkaller #0 PREEMPT_{RT,(full)}
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:io_apic_sync arch/x86/kernel/apic/io_apic.c:398 [inline]
RIP: 0010:io_apic_modify_irq arch/x86/kernel/apic/io_apic.c:386 [inline]
RIP: 0010:mask_ioapic_irq+0x187/0x380 arch/x86/kernel/apic/io_apic.c:407
Code: 10 00 00 00 c1 e5 0c 81 c5 00 40 20 00 48 63 cd 48 c7 c2 00 f0 7f ff 48 29 ca 8b 0b 81 e1 ff 0f 00 00 89 04 0a 44 89 74 0a 10 <41> 0f b6 44 35 00 84 c0 0f 85 2c 01 00 00 44 8b 2f 49 81 fd 80 00
RSP: 0018:ffffc90000007f00 EFLAGS: 00000046
RAX: 0000000000000024 RBX: ffffffff91b73694 RCX: 0000000000000000
RDX: ffffffffff5fb000 RSI: dffffc0000000000 RDI: ffff88813ff7d850
RBP: 0000000000204000 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffff52000000fbc R12: ffff88813ff7d840
R13: 1ffff11027fefb0a R14: 0000000000018020 R15: 000000000000000a
FS: 00007fe5d0c066c0(0000) GS:ffff888126d03000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055f04873d608 CR3: 000000003567c000 CR4: 00000000003526f0
Call Trace:
<IRQ>
mask_irq kernel/irq/chip.c:434 [inline]
handle_fasteoi_irq+0x33f/0xa00 kernel/irq/chip.c:762
generic_handle_irq_desc include/linux/irqdesc.h:172 [inline]
handle_irq arch/x86/kernel/irq.c:255 [inline]
call_irq_handler arch/x86/kernel/irq.c:-1 [inline]
__common_interrupt+0x141/0x1f0 arch/x86/kernel/irq.c:326
common_interrupt+0xb6/0xe0 arch/x86/kernel/irq.c:319
</IRQ>
<TASK>
asm_common_interrupt+0x26/0x40 arch/x86/include/asm/idtentry.h:688
RIP: 0010:arch_atomic_read arch/x86/include/asm/atomic.h:23 [inline]
RIP: 0010:raw_atomic_read include/linux/atomic/atomic-arch-fallback.h:457 [inline]
RIP: 0010:rcu_is_watching_curr_cpu include/linux/context_tracking.h:128 [inline]
RIP: 0010:rcu_is_watching+0x4e/0xb0 kernel/rcu/tree.c:751
Code: ff df 4c 8d 34 dd d0 ad 01 8d 4c 89 f0 48 c1 e8 03 42 80 3c 38 00 74 08 4c 89 f7 e8 ac 92 7c 00 48 c7 c3 58 0c b3 91 49 03 1e <48> 89 d8 48 c1 e8 03 42 0f b6 04 38 84 c0 75 34 8b 03 65 ff 0d 79
RSP: 0018:ffffc90003f074c8 EFLAGS: 00000283
RAX: 1ffffffff1a035ba RBX: ffff8880b8833c58 RCX: f99f3176bf70e500
RDX: 0000000000000000 RSI: ffffffff8b3f5640 RDI: ffffffff8b3f5600
RBP: 0000000000000001 R08: 0000000000000000 R09: 0000000000000000
R10: ffff88803df1b2b8 R11: ffffed1007be365b R12: dffffc0000000000
R13: ffff88803df1b280 R14: ffffffff8d01add0 R15: dffffc0000000000
rcu_read_lock include/linux/rcupdate.h:868 [inline]
bio_associate_blkg+0xa6/0x230 block/blk-cgroup.c:2154
bio_init block/bio.c:267 [inline]
bio_alloc_percpu_cache block/bio.c:473 [inline]
bio_alloc_bioset+0x46a/0x12d0 block/bio.c:526
bio_alloc include/linux/bio.h:374 [inline]
blk_alloc_discard_bio+0x194/0x2c0 block/blk-lib.c:47
__blkdev_issue_discard block/blk-lib.c:68 [inline]
blkdev_issue_discard+0xf2/0x1b0 block/blk-lib.c:93
nilfs_sufile_trim_fs+0xc31/0xf90 fs/nilfs2/sufile.c:1182
nilfs_ioctl_trim_fs fs/nilfs2/ioctl.c:1041 [inline]
nilfs_ioctl+0x1411/0x25a0 fs/nilfs2/ioctl.c:1354
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl+0xff/0x170 fs/ioctl.c:583
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fe5d159f749
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:00007fe5d0c06038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fe5d17f5fa0 RCX: 00007fe5d159f749
RDX: 00002000000004c0 RSI: 00000000c0185879 RDI: 0000000000000005
RBP: 00007fe5d1623f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fe5d17f6038 R14: 00007fe5d17f5fa0 R15: 00007ffff490ff28
</TASK>


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
For information about bisection process see: https://goo.gl/tpsmEJ#bisection

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup

[Edward Adam Davis]

When a user executes the FITRIM command, an underflow can occur when
calculating nblocks if end_block is too small. Since nblocks is of
type sector_t, which is u64, a negative nblocks value will become a
very large positive integer. This ultimately leads to the block layer
function __blkdev_issue_discard() taking an excessively long time to
process the bio chain, and the ns_segctor_sem lock remains held for a
long period. This prevents other tasks from acquiring the ns_segctor_sem
lock, resulting in the hang reported by syzbot in [1].

The fix involves adding a check for the end block: if it equals the
start block, the trim operation is exited and -EINVAL is returned.

[1]

task:segctord state:D stack:28968 pid:6093 tgid:6093 ppid:2 task_flags:0x200040 flags:0x00080000
Call Trace:

rwbase_write_lock+0x3dd/0x750 kernel/locking/rwbase_rt.c:272
nilfs_transaction_lock+0x253/0x4c0 fs/nilfs2/segment.c:357
nilfs_segctor_thread_construct fs/nilfs2/segment.c:2569 [inline]
nilfs_segctor_thread+0x6ec/0xe00 fs/nilfs2/segment.c:2684

Fixes: 82e11e857be3 ("nilfs2: add nilfs_sufile_trim_fs to trim clean segs")
Reported-by: syzbot+7eedce...@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=7eedce5eb281acd832f0
Signed-off-by: Edward Adam Davis <ead...@qq.com>
---
fs/nilfs2/sufile.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/fs/nilfs2/sufile.c b/fs/nilfs2/sufile.c
index 83f93337c01b..63a1f0b29066 100644
--- a/fs/nilfs2/sufile.c
+++ b/fs/nilfs2/sufile.c
@@ -1093,6 +1093,9 @@ int nilfs_sufile_trim_fs(struct inode *sufile, struct fstrim_range *range)
else
end_block = start_block + len - 1;

+ if (start_block == end_block)
+ return -EINVAL;
+
segnum = nilfs_get_segnum_of_block(nilfs, start_block);
segnum_end = nilfs_get_segnum_of_block(nilfs, end_block);

--
2.43.0