============================================
WARNING: possible recursive locking detected
6.13.0-rc4-syzkaller-00110-g4099a71718b0 #0 Not tainted
--------------------------------------------
syz.2.308/7258 is trying to acquire lock:
ffff8881433b3078 (&p->frag_sem){.+.+}-{4:4}, at: __configfs_open_file+0xe8/0x9c0 fs/configfs/file.c:304

but task is already holding lock:
ffff8880270c7378 (&p->frag_sem){.+.+}-{4:4}, at: flush_write_buffer fs/configfs/file.c:205 [inline]
ffff8880270c7378 (&p->frag_sem){.+.+}-{4:4}, at: configfs_write_iter+0x216/0x4b0 fs/configfs/file.c:229

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

       CPU0
       ----
  lock(&p->frag_sem);
  lock(&p->frag_sem);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

5 locks held by syz.2.308/7258:
 #0: ffff88807e6080f8 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x267/0x390 fs/file.c:1191
 #1: ffff88801cf3c420 (sb_writers#16){.+.+}-{0:0}, at: do_writev+0x133/0x340 fs/read_write.c:1096
 #2: ffff88802f3b5c88 (&buffer->mutex){+.+.}-{4:4}, at: configfs_write_iter+0x75/0x4b0 fs/configfs/file.c:226
 #3: ffff8880270c7378 (&p->frag_sem){.+.+}-{4:4}, at: flush_write_buffer fs/configfs/file.c:205 [inline]
 #3: ffff8880270c7378 (&p->frag_sem){.+.+}-{4:4}, at: configfs_write_iter+0x216/0x4b0 fs/configfs/file.c:229
 #4: ffffffff8ee08a88 (target_devices_lock){+.+.}-{4:4}, at: target_core_item_dbroot_store+0x23/0x2e0 drivers/target/target_core_configfs.c:114

stack backtrace:
CPU: 0 UID: 0 PID: 7258 Comm: syz.2.308 Not tainted 6.13.0-rc4-syzkaller-00110-g4099a71718b0 #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+0x116/0x1f0 lib/dump_stack.c:120
 print_deadlock_bug+0x2e3/0x410 kernel/locking/lockdep.c:3037
 check_deadlock kernel/locking/lockdep.c:3089 [inline]
 validate_chain kernel/locking/lockdep.c:3891 [inline]
 __lock_acquire+0x2117/0x3c40 kernel/locking/lockdep.c:5226
 lock_acquire.part.0+0x11b/0x380 kernel/locking/lockdep.c:5849
 down_read+0x9a/0x330 kernel/locking/rwsem.c:1524
 __configfs_open_file+0xe8/0x9c0 fs/configfs/file.c:304
 do_dentry_open+0xf59/0x1ea0 fs/open.c:945
 vfs_open+0x82/0x3f0 fs/open.c:1075
 do_open fs/namei.c:3828 [inline]
 path_openat+0x1e6a/0x2d60 fs/namei.c:3987
 do_filp_open+0x20c/0x470 fs/namei.c:4014
 file_open_name+0x2a4/0x450 fs/open.c:1347
 filp_open+0x4b/0x80 fs/open.c:1367
 target_core_item_dbroot_store+0x10d/0x2e0 drivers/target/target_core_configfs.c:134
 flush_write_buffer fs/configfs/file.c:207 [inline]
 configfs_write_iter+0x2f6/0x4b0 fs/configfs/file.c:229
 do_iter_readv_writev+0x532/0x7f0 fs/read_write.c:820
 vfs_writev+0x363/0xdd0 fs/read_write.c:1050
 do_writev+0x133/0x340 fs/read_write.c:1096
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f537ff85d29
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:00007f5380cd1038 EFLAGS: 00000246 ORIG_RAX: 0000000000000014
RAX: ffffffffffffffda RBX: 00007f5380175fa0 RCX: 00007f537ff85d29
RDX: 0000000000000002 RSI: 0000000020000080 RDI: 0000000000000004
RBP: 00007f5380001b08 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f5380175fa0 R15: 00007ffd4e636c98
 </TASK>
db_root: not a directory: /sys/kernel/config/nullb/features