Re: [syzbot] [ext4?] INFO: task hung in vfs_rmdir (2)

[syzbot <syzbot+42986aeeddfd7ed93c8b@syzkaller.appspotmail.com>]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
INFO: task hung in vfs_rmdir

INFO: task syz-executor:5934 blocked for more than 143 seconds.
      Not tainted 6.9.0-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz-executor    state:D stack:22736 pid:5934  tgid:5932  ppid:5638   flags:0x00000006
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5409 [inline]
 __schedule+0x1796/0x4a00 kernel/sched/core.c:6746
 __schedule_loop kernel/sched/core.c:6823 [inline]
 schedule+0x14b/0x320 kernel/sched/core.c:6838
 schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:6895
 rwsem_down_write_slowpath+0xeeb/0x13b0 kernel/locking/rwsem.c:1178
 __down_write_common+0x1af/0x200 kernel/locking/rwsem.c:1306
 inode_lock include/linux/fs.h:795 [inline]
 vfs_rmdir+0x101/0x4c0 fs/namei.c:4195
 do_rmdir+0x3b5/0x580 fs/namei.c:4265
 __do_sys_rmdir fs/namei.c:4284 [inline]
 __se_sys_rmdir fs/namei.c:4282 [inline]
 __x64_sys_rmdir+0x49/0x60 fs/namei.c:4282
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf5/0x240 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7efe6f27cee9
RSP: 002b:00007efe7003c0c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000054
RAX: ffffffffffffffda RBX: 00007efe6f3b3fa0 RCX: 00007efe6f27cee9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000020000180
RBP: 00007efe6f2c947f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 000000000000000b R14: 00007efe6f3b3fa0 R15: 00007ffcf06a10f8
 </TASK>

Showing all locks held in the system:
1 lock held by khungtaskd/29:
 #0: ffffffff8e334da0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:329 [inline]
 #0: ffffffff8e334da0 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:781 [inline]
 #0: ffffffff8e334da0 (rcu_read_lock){....}-{1:2}, at: debug_show_all_locks+0x55/0x2a0 kernel/locking/lockdep.c:6614
2 locks held by getty/4827:
 #0: ffff88802abe60a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:243
 #1: ffffc90002f162f0 (&ldata->atomic_read_lock){+.+.}-{3:3}, at: n_tty_read+0x6b5/0x1e10 drivers/tty/n_tty.c:2201
3 locks held by syz-executor/5934:
 #0: ffff888020866420 (sb_writers#12){.+.+}-{0:0}, at: mnt_want_write+0x3f/0x90 fs/namespace.c:409
 #1: ffff88807f131650 (&sb->s_type->i_mutex_key#20/1){+.+.}-{3:3}, at: inode_lock_nested include/linux/fs.h:830 [inline]
 #1: ffff88807f131650 (&sb->s_type->i_mutex_key#20/1){+.+.}-{3:3}, at: do_rmdir+0x263/0x580 fs/namei.c:4253
 #2: ffff88807f131650 (&sb->s_type->i_mutex_key#21){+.+.}-{3:3}, at: inode_lock include/linux/fs.h:795 [inline]
 #2: ffff88807f131650 (&sb->s_type->i_mutex_key#21){+.+.}-{3:3}, at: vfs_rmdir+0x101/0x4c0 fs/namei.c:4195
4 locks held by syz-executor/5946:

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

NMI backtrace for cpu 0
CPU: 0 PID: 29 Comm: khungtaskd Not tainted 6.9.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/02/2024
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:114
 nmi_cpu_backtrace+0x49c/0x4d0 lib/nmi_backtrace.c:113
 nmi_trigger_cpumask_backtrace+0x198/0x320 lib/nmi_backtrace.c:62
 trigger_all_cpu_backtrace include/linux/nmi.h:160 [inline]
 check_hung_uninterruptible_tasks kernel/hung_task.c:223 [inline]
 watchdog+0xfde/0x1020 kernel/hung_task.c:380
 kthread+0x2f0/0x390 kernel/kthread.c:388
 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
 </TASK>
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 PID: 14944 Comm: syz-executor Not tainted 6.9.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/02/2024
RIP: 0010:ext4_ext_map_blocks+0x7c7/0x77b0 fs/ext4/extents.c:4236
Code: 89 ee e8 1c 4d 46 ff 4d 89 fc 45 29 ef 0f 86 c8 02 00 00 e8 4b 4b 46 ff 45 89 ec 4c 8b 74 24 20 e9 07 21 00 00 48 8b 44 24 70 <42> 0f b6 04 38 84 c0 0f 85 2f 4c 00 00 48 8b 44 24 18 44 8b 30 48
RSP: 0018:ffffc90003ef74c0 EFLAGS: 00000202
RAX: 1ffff920007def39 RBX: 0000000000000001 RCX: ffff88801166da00
RDX: ffff88801166da00 RSI: 0000000000000001 RDI: 0000000000000000
RBP: ffffc90003ef77d0 R08: ffffffff824fbb51 R09: 0000000000000000
R10: ffff888028cbf110 R11: ffffed1005197e24 R12: 1ffff920007deee2
R13: 0000000000000000 R14: 0000000000000000 R15: dffffc0000000000
FS:  00007ff4d35a56c0(0000) GS:ffff8880b9500000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 0000000026118000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <NMI>
 </NMI>
 <TASK>
 ext4_map_blocks+0xa5e/0x1d20 fs/ext4/inode.c:623
 ext4_getblk+0x1fa/0x850 fs/ext4/inode.c:833
 ext4_bread+0x2e/0x180 fs/ext4/inode.c:889
 ext4_append+0x327/0x5c0 fs/ext4/namei.c:83
 ext4_init_new_dir+0x33e/0xa30 fs/ext4/namei.c:2977
 ext4_mkdir+0x4f7/0xcf0 fs/ext4/namei.c:3023
 vfs_mkdir+0x2f9/0x4b0 fs/namei.c:4123
 do_mkdirat+0x264/0x3a0 fs/namei.c:4146
 __do_sys_mkdirat fs/namei.c:4161 [inline]
 __se_sys_mkdirat fs/namei.c:4159 [inline]
 __x64_sys_mkdirat+0x89/0xa0 fs/namei.c:4159
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf5/0x240 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7ff4d287b9e7
Code: 73 01 c3 48 c7 c1 b0 ff ff ff f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 b8 02 01 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ff4d35a4ef8 EFLAGS: 00000246 ORIG_RAX: 0000000000000102
RAX: ffffffffffffffda RBX: 00007ff4d35a4f80 RCX: 00007ff4d287b9e7
RDX: 00000000000001ff RSI: 0000000020000180 RDI: 00000000ffffff9c
RBP: 0000000020000100 R08: 00000000200001c0 R09: 0000000000000000
R10: 0000000020000100 R11: 0000000000000246 R12: 0000000020000180
R13: 00007ff4d35a4f40 R14: 0000000000000000 R15: 0000000000000000
 </TASK>


Tested on:

commit:         a38297e3 Linux 6.9
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6 v6.9
console output: https://syzkaller.appspot.com/x/log.txt?x=117bca16980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=df13071aee1d0001
dashboard link: https://syzkaller.appspot.com/bug?extid=42986aeeddfd7ed93c8b
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40

Note: no patches were applied.