============================================
WARNING: possible recursive locking detected
syzkaller #0 Not tainted
--------------------------------------------
syz.0.0/5336 is trying to acquire lock:
ffff888012816520 (&sbi->s_alloc_mutex){+.+.}-{4:4}, at: udf_table_free_blocks fs/udf/balloc.c:376 [inline]
ffff888012816520 (&sbi->s_alloc_mutex){+.+.}-{4:4}, at: udf_free_blocks+0xa8c/0x1900 fs/udf/balloc.c:678

but task is already holding lock:
ffff888012816520 (&sbi->s_alloc_mutex){+.+.}-{4:4}, at: udf_table_prealloc_blocks fs/udf/balloc.c:517 [inline]
ffff888012816520 (&sbi->s_alloc_mutex){+.+.}-{4:4}, at: udf_prealloc_blocks+0x8ea/0x10e0 fs/udf/balloc.c:702

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.0.0/5336:
 #0: ffff888042270450 (sb_writers#12){.+.+}-{0:0}, at: file_start_write include/linux/fs.h:2733 [inline]
 #0: ffff888042270450 (sb_writers#12){.+.+}-{0:0}, at: vfs_writev+0x2af/0x990 fs/read_write.c:1056
 #1: ffff888044543628 (&sb->s_type->i_mutex_key#24){+.+.}-{4:4}, at: inode_lock include/linux/fs.h:1024 [inline]
 #1: ffff888044543628 (&sb->s_type->i_mutex_key#24){+.+.}-{4:4}, at: udf_file_write_iter+0x75/0x6c0 fs/udf/file.c:96
 #2: ffff888044543408 (&ei->i_data_sem#3){++++}-{4:4}, at: udf_map_block+0x29c/0x4280 fs/udf/inode.c:445
 #3: ffff888012816520 (&sbi->s_alloc_mutex){+.+.}-{4:4}, at: udf_table_prealloc_blocks fs/udf/balloc.c:517 [inline]
 #3: ffff888012816520 (&sbi->s_alloc_mutex){+.+.}-{4:4}, at: udf_prealloc_blocks+0x8ea/0x10e0 fs/udf/balloc.c:702

stack backtrace:
CPU: 0 UID: 0 PID: 5336 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 04/01/2014
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 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+0x24df/0x2cf0 kernel/locking/lockdep.c:5237
 lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5868
 __mutex_lock_common kernel/locking/mutex.c:646 [inline]
 __mutex_lock+0x19d/0x1550 kernel/locking/mutex.c:821
 udf_table_free_blocks fs/udf/balloc.c:376 [inline]
 udf_free_blocks+0xa8c/0x1900 fs/udf/balloc.c:678
 udf_delete_aext+0x4f5/0xc00 fs/udf/inode.c:2381
 udf_table_prealloc_blocks fs/udf/balloc.c:544 [inline]
 udf_prealloc_blocks+0xbd4/0x10e0 fs/udf/balloc.c:702
 udf_prealloc_extents fs/udf/inode.c:1058 [inline]
 inode_getblk fs/udf/inode.c:916 [inline]
 udf_map_block+0x1e7f/0x4280 fs/udf/inode.c:453
 __udf_get_block+0x52/0x250 fs/udf/inode.c:467
 get_more_blocks fs/direct-io.c:644 [inline]
 do_direct_IO fs/direct-io.c:932 [inline]
 __blockdev_direct_IO+0x1590/0x3380 fs/direct-io.c:1236
 blockdev_direct_IO include/linux/fs.h:3135 [inline]
 udf_direct_IO+0x139/0x200 fs/udf/inode.c:311
 generic_file_direct_write+0x1d0/0x3f0 mm/filemap.c:4292
 __generic_file_write_iter+0x11d/0x230 mm/filemap.c:4461
 udf_file_write_iter+0x2e8/0x6c0 fs/udf/file.c:112
 do_iter_readv_writev+0x612/0x8c0 fs/read_write.c:-1
 vfs_writev+0x343/0x990 fs/read_write.c:1058
 do_pwritev fs/read_write.c:1154 [inline]
 __do_sys_pwritev2 fs/read_write.c:1212 [inline]
 __se_sys_pwritev2+0x177/0x2a0 fs/read_write.c:1203
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f90f059e0d9
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f90f1384fe8 EFLAGS: 00000246 ORIG_RAX: 0000000000000148
RAX: ffffffffffffffda RBX: 00007f90f0826090 RCX: 00007f90f059e0d9
RDX: 0000000000000001 RSI: 0000200000000240 RDI: 000000000000000b
RBP: 00007f90f0635024 R08: 0000000000000000 R09: 0000000000000003
R10: 0000000000002000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f90f0826128 R14: 00007f90f0826090 R15: 00007ffc77b20fd8
 </TASK>