[syzbot] [fs?] possible deadlock in __configfs_open_file

[syzbot <syzbot+f6e8174215573a84b797@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    eabcdba3ad40 Merge tag 'for-6.13-rc3-tag' of git://git.ker..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17791f44580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=c22efbd20f8da769
dashboard link: https://syzkaller.appspot.com/bug?extid=f6e8174215573a84b797
compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1449ccf8580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=14a37730580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/a9904ed2be77/disk-eabcdba3.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/fb8d571e1cb3/vmlinux-eabcdba3.xz
kernel image: https://storage.googleapis.com/syzbot-assets/76349070db25/bzImage-eabcdba3.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f6e8174215573a84b797@syzkaller.appspotmail.com

============================================
WARNING: possible recursive locking detected
6.13.0-rc3-syzkaller-00073-geabcdba3ad40 #0 Not tainted
--------------------------------------------
syz-executor381/5829 is trying to acquire lock:
ffff8880268ded78 (&p->frag_sem){.+.+}-{4:4}, at: __configfs_open_file+0xe8/0x9c0 fs/configfs/file.c:304

but task is already holding lock:
ffff8880268ded78 (&p->frag_sem){.+.+}-{4:4}, at: flush_write_buffer fs/configfs/file.c:205 [inline]
ffff8880268ded78 (&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

4 locks held by syz-executor381/5829:
 #0: ffff88801e7f0420 (sb_writers#9){.+.+}-{0:0}, at: ksys_write+0x12b/0x250 fs/read_write.c:731
 #1: ffff888026d52688 (&buffer->mutex){+.+.}-{4:4}, at: configfs_write_iter+0x75/0x4b0 fs/configfs/file.c:226
 #2: ffff8880268ded78 (&p->frag_sem){.+.+}-{4:4}, at: flush_write_buffer fs/configfs/file.c:205 [inline]
 #2: ffff8880268ded78 (&p->frag_sem){.+.+}-{4:4}, at: configfs_write_iter+0x216/0x4b0 fs/configfs/file.c:229
 #3: ffffffff8ee089c8 (target_devices_lock){+.+.}-{4:4}, at: target_core_item_dbroot_store+0x23/0x2e0 drivers/target/target_core_configfs.c:114

stack backtrace:
CPU: 1 UID: 0 PID: 5829 Comm: syz-executor381 Not tainted 6.13.0-rc3-syzkaller-00073-geabcdba3ad40 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/25/2024
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
 new_sync_write fs/read_write.c:586 [inline]
 vfs_write+0x5ae/0x1150 fs/read_write.c:679
 ksys_write+0x12b/0x250 fs/read_write.c:731
 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: 0033:0x7f70a1169979
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 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffcb84c8f08 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f70a11b3300 RCX: 00007f70a1169979
RDX: 0000000000000080 RSI: 0000000020000040 RDI: 0000000000000003
RBP: 00007f70a11b30fd R08: 0000000000000006 R09: 0000000000000006
R10: 0000000000000006 R11: 0000000000000246 R12: 00007f70a11b817c


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