Re: [syzbot] [udf?] possible deadlock in udf_free_blocks

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
WARNING: bad unlock balance in udf_free_blocks

=====================================
WARNING: bad unlock balance detected!
6.15.0-rc2-syzkaller-00042-g1a1d569a75f3-dirty #0 Not tainted
-------------------------------------
syz.0.17/6157 is trying to release lock (&sbi->s_alloc_mutex) at:
[<ffffffff834e835e>] udf_free_blocks+0x25e/0x23b0 fs/udf/balloc.c:678
but there are no more locks to release!

other info that might help us debug this:
3 locks held by syz.0.17/6157:
 #0: ffff88806ddbc420 (sb_writers#12){.+.+}-{0:0}, at: direct_splice_actor+0x49/0x220 fs/splice.c:1157
 #1: ffff88805f0795c0 (&sb->s_type->i_mutex_key#21){+.+.}-{4:4}, at: inode_lock include/linux/fs.h:867 [inline]
 #1: ffff88805f0795c0 (&sb->s_type->i_mutex_key#21){+.+.}-{4:4}, at: udf_file_write_iter+0x6d/0x6c0 fs/udf/file.c:95
 #2: ffff88805f0793f0 (&ei->i_data_sem#2){++++}-{4:4}, at: udf_map_block+0x3b9/0x53f0 fs/udf/inode.c:439

stack backtrace:
CPU: 1 UID: 0 PID: 6157 Comm: syz.0.17 Not tainted 6.15.0-rc2-syzkaller-00042-g1a1d569a75f3-dirty #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
 print_unlock_imbalance_bug+0x185/0x1a0 kernel/locking/lockdep.c:5296
 __lock_release kernel/locking/lockdep.c:5535 [inline]
 lock_release+0x1ed/0x3e0 kernel/locking/lockdep.c:5887
 __mutex_unlock_slowpath+0xee/0x800 kernel/locking/mutex.c:907
 udf_free_blocks+0x25e/0x23b0 fs/udf/balloc.c:678
 udf_merge_extents fs/udf/inode.c:1143 [inline]
 inode_getblk fs/udf/inode.c:914 [inline]
 udf_map_block+0x3061/0x53f0 fs/udf/inode.c:447
 __udf_get_block+0x128/0x410 fs/udf/inode.c:461
 __block_write_begin_int+0x693/0x1930 fs/buffer.c:2116
 block_write_begin+0x8f/0x120 fs/buffer.c:2227
 udf_write_begin+0xfc/0x250 fs/udf/inode.c:256
 generic_perform_write+0x32b/0xa10 mm/filemap.c:4102
 udf_file_write_iter+0x2e7/0x6c0 fs/udf/file.c:111
 iter_file_splice_write+0xbe1/0x1530 fs/splice.c:738
 do_splice_from fs/splice.c:935 [inline]
 direct_splice_actor+0x11d/0x220 fs/splice.c:1158
 splice_direct_to_actor+0x597/0xc90 fs/splice.c:1102
 do_splice_direct_actor fs/splice.c:1201 [inline]
 do_splice_direct+0x281/0x3d0 fs/splice.c:1227
 do_sendfile+0x582/0x8c0 fs/read_write.c:1368
 __do_sys_sendfile64 fs/read_write.c:1429 [inline]
 __se_sys_sendfile64+0x17e/0x1e0 fs/read_write.c:1415
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fedc3385d29
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:00007fedc41b4038 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 00007fedc3576080 RCX: 00007fedc3385d29
RDX: 0000000000000000 RSI: 0000000000000006 RDI: 0000000000000005
RBP: 00007fedc3401aa8 R08: 0000000000000000 R09: 0000000000000000
R10: 0001000000201005 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007fedc3576080 R15: 00007ffc4f30ca78
 </TASK>


Tested on:

commit:         1a1d569a Merge tag 'edac_urgent_for_v6.15_rc3' of git:..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16f90b98580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=5dd916f7ca732ed
dashboard link: https://syzkaller.appspot.com/bug?extid=d472c32c5dd4cd2fb5c5
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=17c60b98580000