============================================
WARNING: possible recursive locking detected
syzkaller #0 Not tainted
--------------------------------------------
syz.0.0/5369 is trying to acquire lock:
ffff888040487d28 (&sbi->s_alloc_mutex){+.+.}-{4:4}, at: udf_table_free_blocks fs/udf/balloc.c:375 [inline]
ffff888040487d28 (&sbi->s_alloc_mutex){+.+.}-{4:4}, at: udf_free_blocks+0x9e2/0x17f0 fs/udf/balloc.c:677

but task is already holding lock:
ffff888040487d28 (&sbi->s_alloc_mutex){+.+.}-{4:4}, at: udf_table_new_block fs/udf/balloc.c:581 [inline]
ffff888040487d28 (&sbi->s_alloc_mutex){+.+.}-{4:4}, at: udf_new_block+0xfab/0x1ba0 fs/udf/balloc.c:725

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.0.0/5369:
 #0: ffff888011884428 (sb_writers#12){.+.+}-{0:0}, at: vfs_coredump+0x1daa/0x2a50 fs/coredump.c:1168
 #1: ffff888044d92280 (&sb->s_type->i_mutex_key#20){+.+.}-{4:4}, at: inode_lock include/linux/fs.h:869 [inline]
 #1: ffff888044d92280 (&sb->s_type->i_mutex_key#20){+.+.}-{4:4}, at: udf_file_write_iter+0x6e/0x6c0 fs/udf/file.c:95
 #2: ffff888044d920b0 (&ei->i_data_sem#2){++++}-{4:4}, at: udf_map_block+0x283/0x45f0 fs/udf/inode.c:446
 #3: ffff888040487d28 (&sbi->s_alloc_mutex){+.+.}-{4:4}, at: udf_table_new_block fs/udf/balloc.c:581 [inline]
 #3: ffff888040487d28 (&sbi->s_alloc_mutex){+.+.}-{4:4}, at: udf_new_block+0xfab/0x1ba0 fs/udf/balloc.c:725

stack backtrace:
CPU: 0 UID: 0 PID: 5369 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+0x28b/0x2a0 kernel/locking/lockdep.c:3041
 check_deadlock kernel/locking/lockdep.c:3093 [inline]
 validate_chain+0x1a3f/0x2140 kernel/locking/lockdep.c:3895
 __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237
 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
 __mutex_lock_common kernel/locking/mutex.c:598 [inline]
 __mutex_lock+0x187/0x1350 kernel/locking/mutex.c:760
 udf_table_free_blocks fs/udf/balloc.c:375 [inline]
 udf_free_blocks+0x9e2/0x17f0 fs/udf/balloc.c:677
 udf_delete_aext+0x4df/0xbc0 fs/udf/inode.c:2380
 udf_table_new_block fs/udf/balloc.c:645 [inline]
 udf_new_block+0x1404/0x1ba0 fs/udf/balloc.c:725
 inode_getblk fs/udf/inode.c:902 [inline]
 udf_map_block+0x13a8/0x45f0 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+0x8a/0x120 fs/buffer.c:2256
 udf_write_begin+0x115/0x270 fs/udf/inode.c:262
 generic_perform_write+0x2c5/0x900 mm/filemap.c:4175
 udf_file_write_iter+0x2d5/0x6c0 fs/udf/file.c:111
 __kernel_write_iter+0x428/0x910 fs/read_write.c:619
 dump_emit_page fs/coredump.c:1296 [inline]
 dump_user_range+0x8a0/0xc90 fs/coredump.c:1370
 elf_core_dump+0x337b/0x3990 fs/binfmt_elf.c:2085
 coredump_write+0x1169/0x1900 fs/coredump.c:1049
 vfs_coredump+0x1daa/0x2a50 fs/coredump.c:1168
 get_signal+0x1109/0x1340 kernel/signal.c:3019
 arch_do_signal_or_restart+0x9a/0x750 arch/x86/kernel/signal.c:337
 exit_to_user_mode_loop kernel/entry/common.c:40 [inline]
 exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]
 irqentry_exit_to_user_mode+0x81/0x120 kernel/entry/common.c:73
 exc_general_protection+0x171/0x200 arch/x86/kernel/traps.c:792
 asm_exc_general_protection+0x26/0x30 arch/x86/include/asm/idtentry.h:617
RIP: 0033:0x7fac5bf8ebf1
Code: 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 83 c8 ff c3 66 2e 0f 1f
RSP: 002b:0000200000000200 EFLAGS: 00010217
RAX: 0000000000000000 RBX: 00007fac5c1b5fa0 RCX: 00007fac5bf8ebe9
RDX: 0000200000000040 RSI: 0000200000000200 RDI: 0000000040000200
RBP: 00007fac5c011e19 R08: 00002000000005c0 R09: 00002000000005c0
R10: 00002000000000c0 R11: 0000000000000206 R12: 0000000000000000
R13: 00007fac5c1b6038 R14: 00007fac5c1b5fa0 R15: 00007ffc1b715648
 </TASK>