[syzbot] [nfs?] [net?] possible deadlock in rpc_close_pipes

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 50c8770a42fa Add linux-next specific files for 20250702
git tree: linux-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=162e7982580000
kernel config: https://syzkaller.appspot.com/x/.config?x=70c16e4e191115d4
dashboard link: https://syzkaller.appspot.com/bug?extid=169de184e9defe7fe709
compiler: Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1247d770580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=17ffe48c580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/3d4ef6bedc5b/disk-50c8770a.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/15b7565dc0ef/vmlinux-50c8770a.xz
kernel image: https://storage.googleapis.com/syzbot-assets/3b397342a62b/bzImage-50c8770a.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+169de1...@syzkaller.appspotmail.com

============================================
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


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

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If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
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If the report is a duplicate of another one, reply with:
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If you want to undo deduplication, reply with:
#syz undup

[Lizhi Xu]

#syz test

diff --git a/net/sunrpc/rpc_pipe.c b/net/sunrpc/rpc_pipe.c
index 0bd1df2ebb47..ae5643e0bc43 100644
--- a/net/sunrpc/rpc_pipe.c
+++ b/net/sunrpc/rpc_pipe.c
@@ -693,7 +693,7 @@ void
rpc_unlink(struct rpc_pipe *pipe)
{
if (pipe->dentry) {
- simple_recursive_removal(pipe->dentry, rpc_close_pipes);
+ locked_recursive_removal(pipe->dentry, rpc_close_pipes);
pipe->dentry = NULL;
}
}

[Hillf Danton]

> Date: Wed, 02 Jul 2025 10:41:32 -0700

> syzbot found the following issue on:
>
> HEAD commit: 50c8770a42fa Add linux-next specific files for 20250702
> git tree: linux-next
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=162e7982580000
> kernel config: https://syzkaller.appspot.com/x/.config?x=70c16e4e191115d4
> dashboard link: https://syzkaller.appspot.com/bug?extid=169de184e9defe7fe709

> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1247d770580000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=17ffe48c580000

#syz test

--- x/net/sunrpc/rpc_pipe.c
+++ y/net/sunrpc/rpc_pipe.c
@@ -175,7 +175,7 @@ rpc_close_pipes(struct dentry *dentry)
int need_release;
LIST_HEAD(free_list);

- inode_lock(inode);
+ inode_lock_nested(inode, 1);
spin_lock(&pipe->lock);
need_release = pipe->nreaders != 0 || pipe->nwriters != 0;
pipe->nreaders = 0;
--

[Lizhi Xu]

#syz test

diff --git a/fs/libfs.c b/fs/libfs.c
index 3bc6c3750b47..0e3e33c4f159 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -611,7 +611,7 @@ static void __simple_recursive_removal(struct dentry *dentry,
struct dentry *victim = NULL, *child;
struct inode *inode = this->d_inode;

- inode_lock(inode);
+ inode_lock_nested(inode, I_MUTEX_CHILD);
if (d_is_dir(this))
inode->i_flags |= S_DEAD;
while ((child = find_next_child(this, victim)) == NULL) {
@@ -624,7 +624,7 @@ static void __simple_recursive_removal(struct dentry *dentry,
this = this->d_parent;
inode = this->d_inode;
if (!locked || victim != dentry)
- inode_lock(inode);
+ inode_lock_nested(inode, I_MUTEX_CHILD);
if (simple_positive(victim)) {
d_invalidate(victim); // avoid lost mounts
if (callback)

[syzbot]

For archival purposes, forwarding an incoming command email to
syzkall...@googlegroups.com.

***

Subject: Re: [syzbot] Re: [syzbot] [nfs?] [net?] possible deadlock in rpc_close_pipes
Author: vi...@zeniv.linux.org.uk

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs.git work.rpc_pipe

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+169de1...@syzkaller.appspotmail.com
Tested-by: syzbot+169de1...@syzkaller.appspotmail.com

Tested on:

commit: 50c8770a Add linux-next specific files for 20250702
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=16ab0c8c580000
kernel config: https://syzkaller.appspot.com/x/.config?x=76d012e863976d4c
dashboard link: https://syzkaller.appspot.com/bug?extid=169de184e9defe7fe709
compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
patch: https://syzkaller.appspot.com/x/patch.diff?x=105dd3d4580000

Note: testing is done by a robot and is best-effort only.

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+169de1...@syzkaller.appspotmail.com
Tested-by: syzbot+169de1...@syzkaller.appspotmail.com

Tested on:

commit: 50c8770a Add linux-next specific files for 20250702
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=1791748c580000

kernel config: https://syzkaller.appspot.com/x/.config?x=76d012e863976d4c
dashboard link: https://syzkaller.appspot.com/bug?extid=169de184e9defe7fe709
compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7

patch: https://syzkaller.appspot.com/x/patch.diff?x=151db48c580000

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+169de1...@syzkaller.appspotmail.com
Tested-by: syzbot+169de1...@syzkaller.appspotmail.com

Tested on:

commit: 50c8770a Add linux-next specific files for 20250702
git tree: linux-next

console output: https://syzkaller.appspot.com/x/log.txt?x=16dff982580000

kernel config: https://syzkaller.appspot.com/x/.config?x=76d012e863976d4c
dashboard link: https://syzkaller.appspot.com/bug?extid=169de184e9defe7fe709
compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7

patch: https://syzkaller.appspot.com/x/patch.diff?x=1336f982580000

[Lizhi Xu]

#syz test

diff --git a/net/sunrpc/rpc_pipe.c b/net/sunrpc/rpc_pipe.c

index 0bd1df2ebb47..e30270e5883a 100644
--- a/net/sunrpc/rpc_pipe.c
+++ b/net/sunrpc/rpc_pipe.c

@@ -175,7 +175,7 @@ rpc_close_pipes(struct dentry *dentry)
int need_release;
LIST_HEAD(free_list);

- inode_lock(inode);
+ inode_lock_nested(inode, I_MUTEX_CHILD);

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+169de1...@syzkaller.appspotmail.com
Tested-by: syzbot+169de1...@syzkaller.appspotmail.com

Tested on:

commit: 350db61f rpc_create_client_dir(): return 0 or -E...
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs.git work.rpc_pipe
console output: https://syzkaller.appspot.com/x/log.txt?x=15970c8c580000
kernel config: https://syzkaller.appspot.com/x/.config?x=af650e21e0ca5e40

dashboard link: https://syzkaller.appspot.com/bug?extid=169de184e9defe7fe709
compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7

Note: no patches were applied.

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+169de1...@syzkaller.appspotmail.com
Tested-by: syzbot+169de1...@syzkaller.appspotmail.com

Tested on:

commit: 8d6c5833 Add linux-next specific files for 20250703
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=130e33d4580000
kernel config: https://syzkaller.appspot.com/x/.config?x=223eb69834aa2df6

dashboard link: https://syzkaller.appspot.com/bug?extid=169de184e9defe7fe709
compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7

patch: https://syzkaller.appspot.com/x/patch.diff?x=14e9748c580000