============================================
WARNING: possible recursive locking detected
syzkaller #0 Not tainted
--------------------------------------------
syz.0.0/5342 is trying to acquire lock:
ffff888037b0c528 (&sbi->s_alloc_mutex){+.+.}-{4:4}, at: udf_table_free_blocks fs/udf/balloc.c:375 [inline]
ffff888037b0c528 (&sbi->s_alloc_mutex){+.+.}-{4:4}, at: udf_free_blocks+0xa8f/0x18e0 fs/udf/balloc.c:677

but task is already holding lock:
ffff888037b0c528 (&sbi->s_alloc_mutex){+.+.}-{4:4}, at: udf_table_prealloc_blocks fs/udf/balloc.c:516 [inline]
ffff888037b0c528 (&sbi->s_alloc_mutex){+.+.}-{4:4}, at: udf_prealloc_blocks+0x8d0/0x10f0 fs/udf/balloc.c:701

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(&sbi->s_alloc_mutex);
  lock(&sbi->s_alloc_mutex);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

4 locks held by syz.0.0/5342:
 #0: ffff8880117ae420 (sb_writers#12){.+.+}-{0:0}, at: direct_splice_actor+0x49/0x160 fs/splice.c:1160
 #1: ffff888047a10f40 (&sb->s_type->i_mutex_key#24){+.+.}-{4:4}, at: inode_lock include/linux/fs.h:1027 [inline]
 #1: ffff888047a10f40 (&sb->s_type->i_mutex_key#24){+.+.}-{4:4}, at: udf_file_write_iter+0x6e/0x6c0 fs/udf/file.c:95
 #2: ffff888047a10d70 (&ei->i_data_sem#2){++++}-{4:4}, at: udf_map_block+0x283/0x45f0 fs/udf/inode.c:446
 #3: ffff888037b0c528 (&sbi->s_alloc_mutex){+.+.}-{4:4}, at: udf_table_prealloc_blocks fs/udf/balloc.c:516 [inline]
 #3: ffff888037b0c528 (&sbi->s_alloc_mutex){+.+.}-{4:4}, at: udf_prealloc_blocks+0x8d0/0x10f0 fs/udf/balloc.c:701

stack backtrace:
CPU: 0 UID: 0 PID: 5342 Comm: syz.0.0 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_deadlock_bug+0x279/0x290 kernel/locking/lockdep.c:3041
 check_deadlock kernel/locking/lockdep.c:3093 [inline]
 validate_chain kernel/locking/lockdep.c:3895 [inline]
 __lock_acquire+0x2540/0x2cf0 kernel/locking/lockdep.c:5237
 lock_acquire+0x117/0x340 kernel/locking/lockdep.c:5868
 __mutex_lock_common kernel/locking/mutex.c:614 [inline]
 __mutex_lock+0x187/0x1350 kernel/locking/mutex.c:776
 udf_table_free_blocks fs/udf/balloc.c:375 [inline]
 udf_free_blocks+0xa8f/0x18e0 fs/udf/balloc.c:677
 udf_delete_aext+0x4df/0xbc0 fs/udf/inode.c:2383
 udf_table_prealloc_blocks fs/udf/balloc.c:543 [inline]
 udf_prealloc_blocks+0xbb4/0x10f0 fs/udf/balloc.c:701
 udf_prealloc_extents fs/udf/inode.c:1060 [inline]
 inode_getblk fs/udf/inode.c:918 [inline]
 udf_map_block+0x1f70/0x45f0 fs/udf/inode.c:454
 __udf_get_block+0x52/0x250 fs/udf/inode.c:468
 __block_write_begin_int+0x6b5/0x1900 fs/buffer.c:2145
 block_write_begin+0x8d/0x120 fs/buffer.c:2256
 udf_write_begin+0x118/0x270 fs/udf/inode.c:262
 generic_perform_write+0x2c5/0x900 mm/filemap.c:4314
 __generic_file_write_iter+0x1ae/0x230 mm/filemap.c:4428
 udf_file_write_iter+0x2d5/0x6c0 fs/udf/file.c:111
 iter_file_splice_write+0x972/0x10b0 fs/splice.c:738
 do_splice_from fs/splice.c:938 [inline]
 direct_splice_actor+0x101/0x160 fs/splice.c:1161
 splice_direct_to_actor+0x5a8/0xcc0 fs/splice.c:1105
 do_splice_direct_actor fs/splice.c:1204 [inline]
 do_splice_direct+0x181/0x270 fs/splice.c:1230
 do_sendfile+0x4da/0x7e0 fs/read_write.c:1370
 __do_sys_sendfile64 fs/read_write.c:1431 [inline]
 __se_sys_sendfile64+0x13e/0x190 fs/read_write.c:1417
 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: 0033:0x7fcf31b8f7c9
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:00007fcf329e3038 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 00007fcf31de6090 RCX: 00007fcf31b8f7c9
RDX: 0000000000000000 RSI: 0000000000000004 RDI: 0000000000000004
RBP: 00007fcf31c13f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000800000009 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fcf31de6128 R14: 00007fcf31de6090 R15: 00007fff92e9f428
 </TASK>