syzbot

======================================================
WARNING: possible circular locking dependency detected
6.13.0-rc4-syzkaller-00004-gf07044dd0df0 #0 Not tainted
------------------------------------------------------
syz.8.2762/15724 is trying to acquire lock:
ffff88805767a1f0 (&sb->s_type->i_mutex_key#30){++++}-{4:4}, at: inode_lock include/linux/fs.h:818 [inline]
ffff88805767a1f0 (&sb->s_type->i_mutex_key#30){++++}-{4:4}, at: __generic_file_fsync+0x97/0x1a0 fs/libfs.c:1536

but task is already holding lock:
ffff888143bd1438 (&q->q_usage_counter(io)#26){++++}-{0:0}, at: loop_set_status+0x1e4/0x8f0 drivers/block/loop.c:1267

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&q->q_usage_counter(io)#26){++++}-{0:0}:
       lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5849
       bio_queue_enter block/blk.h:75 [inline]
       blk_mq_submit_bio+0x1536/0x2390 block/blk-mq.c:3090
       __submit_bio+0x2c6/0x560 block/blk-core.c:629
       __submit_bio_noacct_mq block/blk-core.c:710 [inline]
       submit_bio_noacct_nocheck+0x4d3/0xe30 block/blk-core.c:739
       fat_sync_bhs+0x6a/0x1e0 fs/fat/misc.c:367
       fat_alloc_clusters+0xd60/0x11c0 fs/fat/fatent.c:541
       fat_alloc_new_dir+0x1a1/0xe60 fs/fat/dir.c:1156
       vfat_mkdir+0x169/0x330 fs/fat/namei_vfat.c:859
       vfs_mkdir+0x2fb/0x4f0 fs/namei.c:4311
       do_mkdirat+0x264/0x3a0 fs/namei.c:4334
       __do_sys_mkdirat fs/namei.c:4349 [inline]
       __se_sys_mkdirat fs/namei.c:4347 [inline]
       __x64_sys_mkdirat+0x87/0xa0 fs/namei.c:4347
       do_syscall_x64 arch/x86/entry/common.c:52 [inline]
       do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&sbi->s_lock){+.+.}-{4:4}:
       lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5849
       __mutex_lock_common kernel/locking/mutex.c:585 [inline]
       __mutex_lock+0x1ac/0xee0 kernel/locking/mutex.c:735
       vfat_lookup+0xee/0x4f0 fs/fat/namei_vfat.c:710
       lookup_open fs/namei.c:3627 [inline]
       open_last_lookups fs/namei.c:3748 [inline]
       path_openat+0x11a9/0x3590 fs/namei.c:3984
       do_filp_open+0x27f/0x4e0 fs/namei.c:4014
       do_sys_openat2+0x13e/0x1d0 fs/open.c:1402
       do_sys_open fs/open.c:1417 [inline]
       __do_sys_open fs/open.c:1425 [inline]
       __se_sys_open fs/open.c:1421 [inline]
       __x64_sys_open+0x225/0x270 fs/open.c:1421
       do_syscall_x64 arch/x86/entry/common.c:52 [inline]
       do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&sb->s_type->i_mutex_key#30){++++}-{4:4}:
       check_prev_add kernel/locking/lockdep.c:3161 [inline]
       check_prevs_add kernel/locking/lockdep.c:3280 [inline]
       validate_chain+0x18ef/0x5920 kernel/locking/lockdep.c:3904
       __lock_acquire+0x1397/0x2100 kernel/locking/lockdep.c:5226
       lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5849
       down_write+0x99/0x220 kernel/locking/rwsem.c:1577
       inode_lock include/linux/fs.h:818 [inline]
       __generic_file_fsync+0x97/0x1a0 fs/libfs.c:1536
       fat_file_fsync+0x7b/0x190 fs/fat/file.c:191
       __loop_update_dio+0x1a4/0x500 drivers/block/loop.c:204
       loop_set_status+0x62b/0x8f0 drivers/block/loop.c:1289
       lo_ioctl+0xcbc/0x1f50
       blkdev_ioctl+0x57f/0x6a0 block/ioctl.c:693
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:906 [inline]
       __se_sys_ioctl+0xf7/0x170 fs/ioctl.c:892
       do_syscall_x64 arch/x86/entry/common.c:52 [inline]
       do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Chain exists of:
  &sb->s_type->i_mutex_key#30 --> &sbi->s_lock --> &q->q_usage_counter(io)#26

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&q->q_usage_counter(io)#26);
                               lock(&sbi->s_lock);
                               lock(&q->q_usage_counter(io)#26);
  lock(&sb->s_type->i_mutex_key#30);

 *** DEADLOCK ***

3 locks held by syz.8.2762/15724:
 #0: ffff88814051f360 (&lo->lo_mutex){+.+.}-{4:4}, at: loop_set_status+0x2a/0x8f0 drivers/block/loop.c:1251
 #1: ffff888143bd1438 (&q->q_usage_counter(io)#26){++++}-{0:0}, at: loop_set_status+0x1e4/0x8f0 drivers/block/loop.c:1267
 #2: ffff888143bd1470 (&q->q_usage_counter(queue)#10){+.+.}-{0:0}, at: loop_set_status+0x1e4/0x8f0 drivers/block/loop.c:1267

stack backtrace:
CPU: 1 UID: 0 PID: 15724 Comm: syz.8.2762 Not tainted 6.13.0-rc4-syzkaller-00004-gf07044dd0df0 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
 print_circular_bug+0x13a/0x1b0 kernel/locking/lockdep.c:2074
 check_noncircular+0x36a/0x4a0 kernel/locking/lockdep.c:2206
 check_prev_add kernel/locking/lockdep.c:3161 [inline]
 check_prevs_add kernel/locking/lockdep.c:3280 [inline]
 validate_chain+0x18ef/0x5920 kernel/locking/lockdep.c:3904
 __lock_acquire+0x1397/0x2100 kernel/locking/lockdep.c:5226
 lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5849
 down_write+0x99/0x220 kernel/locking/rwsem.c:1577
 inode_lock include/linux/fs.h:818 [inline]
 __generic_file_fsync+0x97/0x1a0 fs/libfs.c:1536
 fat_file_fsync+0x7b/0x190 fs/fat/file.c:191
 __loop_update_dio+0x1a4/0x500 drivers/block/loop.c:204
 loop_set_status+0x62b/0x8f0 drivers/block/loop.c:1289
 lo_ioctl+0xcbc/0x1f50
 blkdev_ioctl+0x57f/0x6a0 block/ioctl.c:693
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:906 [inline]
 __se_sys_ioctl+0xf7/0x170 fs/ioctl.c:892
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fb0c1785d29
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:00007fb0c2540038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fb0c1976080 RCX: 00007fb0c1785d29
RDX: 0000000020000480 RSI: 0000000000004c02 RDI: 0000000000000004
RBP: 00007fb0c1801aa8 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000001 R14: 00007fb0c1976080 R15: 00007ffc4f813998
 </TASK>