Kernel bug: possible deadlock in rpc_close_pipes
Subsystem: nfs, net
Status: fixed

Crash report:
============================================
WARNING: possible recursive locking detected
6.16.0-rc4-next-20250702-syzkaller #0 Not tainted
--------------------------------------------
syz-executor309/5837 is trying to acquire lock:
ffff88807f5bc8c8 (&sb->s_type->i_mutex_key#15){+.+.}-{4:4}, at: inode_lock include/linux/fs.h:869 [inline]
ffff88807f5bc8c8 (&sb->s_type->i_mutex_key#15){+.+.}-{4:4}, at: rpc_close_pipes+0x10a/0x730 net/sunrpc/rpc_pipe.c:178

but task is already holding lock:
ffff88807f5b91c8 (&sb->s_type->i_mutex_key#15){+.+.}-{4:4}, at: inode_lock include/linux/fs.h:869 [inline]
ffff88807f5b91c8 (&sb->s_type->i_mutex_key#15){+.+.}-{4:4}, at: __simple_recursive_removal+0x190/0x510 fs/libfs.c:627

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

       CPU0
       ----
  lock(&sb->s_type->i_mutex_key#15);
  lock(&sb->s_type->i_mutex_key#15);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

4 locks held by syz-executor309/5837:
 #0: ffff888033ee40e0 (&type->s_umount_key#42){+.+.}-{4:4}, at: __super_lock fs/super.c:57 [inline]
 #0: ffff888033ee40e0 (&type->s_umount_key#42){+.+.}-{4:4}, at: __super_lock_excl fs/super.c:72 [inline]
 #0: ffff888033ee40e0 (&type->s_umount_key#42){+.+.}-{4:4}, at: deactivate_super+0xa9/0xe0 fs/super.c:506
 #1: ffff8881446f60a0 (&sn->pipefs_sb_lock){+.+.}-{4:4}, at: rpc_kill_sb+0x77/0x190 net/sunrpc/rpc_pipe.c:1196
 #2: ffffffff8f8e2df0 ((rpc_pipefs_notifier_list).rwsem){++++}-{4:4}, at: blocking_notifier_call_chain+0x54/0x90 kernel/notifier.c:379
 #3: ffff88807f5b91c8 (&sb->s_type->i_mutex_key#15){+.+.}-{4:4}, at: inode_lock include/linux/fs.h:869 [inline]
 #3: ffff88807f5b91c8 (&sb->s_type->i_mutex_key#15){+.+.}-{4:4}, at: __simple_recursive_removal+0x190/0x510 fs/libfs.c:627

stack backtrace:
CPU: 0 UID: 0 PID: 5837 Comm: syz-executor309 Not tainted 6.16.0-rc4-next-20250702-syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_deadlock_bug+0x28b/0x2a0 kernel/locking/lockdep.c:3044
 check_deadlock kernel/locking/lockdep.c:3096 [inline]
 validate_chain+0x1a3f/0x2140 kernel/locking/lockdep.c:3898
 __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5240
 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
 down_write+0x96/0x1f0 kernel/locking/rwsem.c:1577
 inode_lock include/linux/fs.h:869 [inline]
 rpc_close_pipes+0x10a/0x730 net/sunrpc/rpc_pipe.c:178
 __simple_recursive_removal+0x208/0x510 fs/libfs.c:631
 rpc_unlink+0x56/0x80 net/sunrpc/rpc_pipe.c:696
 rpc_pipefs_event+0xc0/0x170 fs/nfs/blocklayout/rpc_pipefs.c:179
 notifier_call_chain+0x1b3/0x3e0 kernel/notifier.c:85
 blocking_notifier_call_chain+0x6a/0x90 kernel/notifier.c:380
 rpc_kill_sb+0xd0/0x190 net/sunrpc/rpc_pipe.c:1204
 deactivate_locked_super+0xb9/0x130 fs/super.c:474
 cleanup_mnt+0x425/0x4c0 fs/namespace.c:1417
 task_work_run+0x1d1/0x260 kernel/task_work.c:227
 ptrace_notify+0x281/0x2c0 kernel/signal.c:2520
 ptrace_report_syscall include/linux/ptrace.h:415 [inline]
 ptrace_report_syscall_exit include/linux/ptrace.h:477 [inline]
 syscall_exit_work+0xc6/0x1d0 kernel/entry/syscall-common.c:111
 syscall_exit_to_user_mode_work include/linux/entry-common.h:173 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:210 [inline]
 do_syscall_64+0x2ad/0x3b0 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f8f7dbc82e9
Code: 48 83 c4 28 c3 e8 37 17 00 00 0f 1f 80 00 00 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:00007ffe287838a8 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffec RBX: 0000200000000000 RCX: 00007f8f7dbc82e9