syzbot

======================================================
WARNING: possible circular locking dependency detected
5.14.0-rc6-syzkaller #0 Not tainted
------------------------------------------------------
systemd-udevd/8720 is trying to acquire lock:
ffffffff8c486d68 (loop_ctl_mutex){+.+.}-{3:3}, at: loop_add+0x9c/0x8c0 drivers/block/loop.c:2316

but task is already holding lock:
ffffffff8c1f4068 (major_names_lock){+.+.}-{3:3}, at: blk_request_module+0x25/0x1d0 block/genhd.c:657

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #3 (major_names_lock){+.+.}-{3:3}:
       __mutex_lock_common kernel/locking/mutex.c:959 [inline]
       __mutex_lock+0x12a/0x10a0 kernel/locking/mutex.c:1104
       __register_blkdev+0x2b/0x3e0 block/genhd.c:216
       register_mtd_blktrans+0x85/0x3c0 drivers/mtd/mtd_blkdevs.c:531
       do_one_initcall+0x103/0x650 init/main.c:1282
       do_initcall_level init/main.c:1355 [inline]
       do_initcalls init/main.c:1371 [inline]
       do_basic_setup init/main.c:1391 [inline]
       kernel_init_freeable+0x6b8/0x741 init/main.c:1593
       kernel_init+0x1a/0x1d0 init/main.c:1485
       ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295

-> #2 (mtd_table_mutex){+.+.}-{3:3}:
       __mutex_lock_common kernel/locking/mutex.c:959 [inline]
       __mutex_lock+0x12a/0x10a0 kernel/locking/mutex.c:1104
       blktrans_open+0x69/0x600 drivers/mtd/mtd_blkdevs.c:210
       blkdev_get_whole+0xa1/0x420 fs/block_dev.c:1253
       blkdev_get_by_dev.part.0+0x30c/0xdd0 fs/block_dev.c:1417
       blkdev_get_by_dev fs/block_dev.c:1506 [inline]
       blkdev_open+0x295/0x300 fs/block_dev.c:1512
       do_dentry_open+0x4c8/0x11d0 fs/open.c:826
       do_open fs/namei.c:3374 [inline]
       path_openat+0x1c23/0x27f0 fs/namei.c:3507
       do_filp_open+0x1aa/0x400 fs/namei.c:3534
       do_sys_openat2+0x16d/0x420 fs/open.c:1204
       do_sys_open fs/open.c:1220 [inline]
       __do_sys_open fs/open.c:1228 [inline]
       __se_sys_open fs/open.c:1224 [inline]
       __x64_sys_open+0x119/0x1c0 fs/open.c:1224
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
       entry_SYSCALL_64_after_hwframe+0x44/0xae

-> #1 (&disk->open_mutex){+.+.}-{3:3}:
       __mutex_lock_common kernel/locking/mutex.c:959 [inline]
       __mutex_lock+0x12a/0x10a0 kernel/locking/mutex.c:1104
       del_gendisk+0x8b/0x770 block/genhd.c:587
       loop_remove drivers/block/loop.c:2413 [inline]
       loop_control_remove drivers/block/loop.c:2462 [inline]
       loop_control_ioctl+0x3b5/0x450 drivers/block/loop.c:2494
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:1069 [inline]
       __se_sys_ioctl fs/ioctl.c:1055 [inline]
       __x64_sys_ioctl+0x193/0x200 fs/ioctl.c:1055
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
       entry_SYSCALL_64_after_hwframe+0x44/0xae

-> #0 (loop_ctl_mutex){+.+.}-{3:3}:
       check_prev_add kernel/locking/lockdep.c:3051 [inline]
       check_prevs_add kernel/locking/lockdep.c:3174 [inline]
       validate_chain kernel/locking/lockdep.c:3789 [inline]
       __lock_acquire+0x2a07/0x54a0 kernel/locking/lockdep.c:5015
       lock_acquire kernel/locking/lockdep.c:5625 [inline]
       lock_acquire+0x1ab/0x510 kernel/locking/lockdep.c:5590
       __mutex_lock_common kernel/locking/mutex.c:959 [inline]
       __mutex_lock+0x12a/0x10a0 kernel/locking/mutex.c:1104
       loop_add+0x9c/0x8c0 drivers/block/loop.c:2316
       loop_probe+0x6a/0x80 drivers/block/loop.c:2426
       blk_request_module+0x111/0x1d0 block/genhd.c:660
       blkdev_get_no_open+0x1d5/0x250 fs/block_dev.c:1334
       blkdev_get_by_dev.part.0+0x25/0xdd0 fs/block_dev.c:1397
       blkdev_get_by_dev fs/block_dev.c:1506 [inline]
       blkdev_open+0x295/0x300 fs/block_dev.c:1512
       do_dentry_open+0x4c8/0x11d0 fs/open.c:826
       do_open fs/namei.c:3374 [inline]
       path_openat+0x1c23/0x27f0 fs/namei.c:3507
       do_filp_open+0x1aa/0x400 fs/namei.c:3534
       do_sys_openat2+0x16d/0x420 fs/open.c:1204
       do_sys_open fs/open.c:1220 [inline]
       __do_sys_open fs/open.c:1228 [inline]
       __se_sys_open fs/open.c:1224 [inline]
       __x64_sys_open+0x119/0x1c0 fs/open.c:1224
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
       entry_SYSCALL_64_after_hwframe+0x44/0xae

other info that might help us debug this:

Chain exists of:
  loop_ctl_mutex --> mtd_table_mutex --> major_names_lock

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(major_names_lock);
                               lock(mtd_table_mutex);
                               lock(major_names_lock);
  lock(loop_ctl_mutex);

 *** DEADLOCK ***

1 lock held by systemd-udevd/8720:
 #0: ffffffff8c1f4068 (major_names_lock){+.+.}-{3:3}, at: blk_request_module+0x25/0x1d0 block/genhd.c:657

stack backtrace:
CPU: 0 PID: 8720 Comm: systemd-udevd Not tainted 5.14.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:105
 check_noncircular+0x25f/0x2e0 kernel/locking/lockdep.c:2131
 check_prev_add kernel/locking/lockdep.c:3051 [inline]
 check_prevs_add kernel/locking/lockdep.c:3174 [inline]
 validate_chain kernel/locking/lockdep.c:3789 [inline]
 __lock_acquire+0x2a07/0x54a0 kernel/locking/lockdep.c:5015
 lock_acquire kernel/locking/lockdep.c:5625 [inline]
 lock_acquire+0x1ab/0x510 kernel/locking/lockdep.c:5590
 __mutex_lock_common kernel/locking/mutex.c:959 [inline]
 __mutex_lock+0x12a/0x10a0 kernel/locking/mutex.c:1104
 loop_add+0x9c/0x8c0 drivers/block/loop.c:2316
 loop_probe+0x6a/0x80 drivers/block/loop.c:2426
 blk_request_module+0x111/0x1d0 block/genhd.c:660
 blkdev_get_no_open+0x1d5/0x250 fs/block_dev.c:1334
 blkdev_get_by_dev.part.0+0x25/0xdd0 fs/block_dev.c:1397
 blkdev_get_by_dev fs/block_dev.c:1506 [inline]
 blkdev_open+0x295/0x300 fs/block_dev.c:1512
 do_dentry_open+0x4c8/0x11d0 fs/open.c:826
 do_open fs/namei.c:3374 [inline]
 path_openat+0x1c23/0x27f0 fs/namei.c:3507
 do_filp_open+0x1aa/0x400 fs/namei.c:3534
 do_sys_openat2+0x16d/0x420 fs/open.c:1204
 do_sys_open fs/open.c:1220 [inline]
 __do_sys_open fs/open.c:1228 [inline]
 __se_sys_open fs/open.c:1224 [inline]
 __x64_sys_open+0x119/0x1c0 fs/open.c:1224
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x7fc70f33e840
Code: 73 01 c3 48 8b 0d 68 77 20 00 f7 d8 64 89 01 48 83 c8 ff c3 66 0f 1f 44 00 00 83 3d 89 bb 20 00 00 75 10 b8 02 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 31 c3 48 83 ec 08 e8 1e f6 ff ff 48 89 04 24
RSP: 002b:00007ffce3344508 EFLAGS: 00000246 ORIG_RAX: 0000000000000002
RAX: ffffffffffffffda RBX: 00005599372d2270 RCX: 00007fc70f33e840
RDX: 0000559936817fe3 RSI: 00000000000a0800 RDI: 00005599372d1f80
RBP: 00007ffce3344680 R08: 0000559936817670 R09: 0000000000000010
R10: 00007fc70f0b8d70 R11: 0000000000000246 R12: 00007ffce33445d0
R13: 00005599372d2370 R14: 0000000000000003 R15: 000000000000000e
----------------
Code disassembly (best guess):
   0:	73 01                	jae    0x3
   2:	c3                   	retq   
   3:	48 8b 0d 68 77 20 00 	mov    0x207768(%rip),%rcx        # 0x207772
   a:	f7 d8                	neg    %eax
   c:	64 89 01             	mov    %eax,%fs:(%rcx)
   f:	48 83 c8 ff          	or     $0xffffffffffffffff,%rax
  13:	c3                   	retq   
  14:	66 0f 1f 44 00 00    	nopw   0x0(%rax,%rax,1)
  1a:	83 3d 89 bb 20 00 00 	cmpl   $0x0,0x20bb89(%rip)        # 0x20bbaa
  21:	75 10                	jne    0x33
  23:	b8 02 00 00 00       	mov    $0x2,%eax
  28:	0f 05                	syscall 
  2a:	48 3d 01 f0 ff ff    	cmp    $0xfffffffffffff001,%rax <-- trapping instruction
  30:	73 31                	jae    0x63
  32:	c3                   	retq   
  33:	48 83 ec 08          	sub    $0x8,%rsp
  37:	e8 1e f6 ff ff       	callq  0xfffff65a
  3c:	48 89 04 24          	mov    %rax,(%rsp)