Message-ID: <6865b1d8.a70a0220.5d25f.06c3.GAE@google.com>
Date: Wed, 02 Jul 2025 15:25:28 -0700
From: syzbot <syzbot+268eaa983b2fb27e5e38@...kaller.appspotmail.com>
To: joel.granados@...nel.org, kees@...nel.org, linux-fsdevel@...r.kernel.org, 
	linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [fs?] WARNING: suspicious RCU usage in proc_sys_compare

syzbot has found a reproducer for 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=1656b48c580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=d831c9dfe03f77ec
dashboard link: https://syzkaller.appspot.com/bug?extid=268eaa983b2fb27e5e38
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=117a148c580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1050f982580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/eb40fda2e0ca/disk-50c8770a.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/cba4d214940c/vmlinux-50c8770a.xz
kernel image: https://storage.googleapis.com/syzbot-assets/4b23ed647866/bzImage-50c8770a.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+268eaa983b2fb27e5e38@...kaller.appspotmail.com

=============================
WARNING: suspicious RCU usage
6.16.0-rc4-next-20250702-syzkaller #0 Not tainted
-----------------------------
fs/proc/proc_sysctl.c:934 suspicious rcu_dereference_check() usage!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 1
3 locks held by syz-executor847/5848:
 #0: ffff88805c84c428 (sb_writers#3){.+.+}-{0:0}, at: mnt_want_write+0x41/0x90 fs/namespace.c:557
 #1: ffff888030198c30 (&sb->s_type->i_mutex_key#10){++++}-{4:4}, at: inode_lock_shared include/linux/fs.h:884 [inline]
 #1: ffff888030198c30 (&sb->s_type->i_mutex_key#10){++++}-{4:4}, at: open_last_lookups fs/namei.c:3806 [inline]
 #1: ffff888030198c30 (&sb->s_type->i_mutex_key#10){++++}-{4:4}, at: path_openat+0x8cb/0x3830 fs/namei.c:4043
 #2: ffff88805d995560 (&lockref->lock){+.+.}-{3:3}, at: spin_lock include/linux/spinlock.h:351 [inline]
 #2: ffff88805d995560 (&lockref->lock){+.+.}-{3:3}, at: d_alloc_parallel+0xace/0x15e0 fs/dcache.c:2623

stack backtrace:
CPU: 1 UID: 0 PID: 5848 Comm: syz-executor847 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
 lockdep_rcu_suspicious+0x140/0x1d0 kernel/locking/lockdep.c:6871
 proc_sys_compare+0x27d/0x2c0 fs/proc/proc_sysctl.c:934
 d_same_name fs/dcache.c:2179 [inline]
 d_alloc_parallel+0x1060/0x15e0 fs/dcache.c:2637
 lookup_open fs/namei.c:3630 [inline]
 open_last_lookups fs/namei.c:3807 [inline]
 path_openat+0xa3b/0x3830 fs/namei.c:4043
 do_filp_open+0x1fa/0x410 fs/namei.c:4073
 do_sys_openat2+0x121/0x1c0 fs/open.c:1434
 do_sys_open fs/open.c:1449 [inline]
 __do_sys_openat fs/open.c:1465 [inline]
 __se_sys_openat fs/open.c:1460 [inline]
 __x64_sys_openat+0x138/0x170 fs/open.c:1460
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7faf9ff7a291
Code: 75 57 89 f0 25 00 00 41 00 3d 00 00 41 00 74 49 80 3d da ab 08 00 00 74 6d 89 da 48 89 ee bf 9c ff ff ff b8 01 01 00 00 0f 05 <48> 3d 00 f0 ff ff 0f 87 93 00 00 00 48 8b 54 24 28 64 48 2b 14 25
RSP: 002b:00007fff03f8f390 EFLAGS: 00000202 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 0000000000080001 RCX: 00007faf9ff7a291
RDX: 0000000000080001 RSI: 00007faf9ffcb7d7 RDI: 00000000ffffff9c
RBP: 00007faf9ffcb7d7 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 00007fff03f8f430
R13: 00007faf9fffa590 R14: 0000000000000000 R15: 0000000000000001
 </TASK>
chnl_net:caif_netlink_parms(): no params data found
bridge0: port 1(bridge_slave_0) entered blocking state
bridge0: port 1(bridge_slave_0) entered disabled state
bridge_slave_0: entered allmulticast mode
bridge_slave_0: entered promiscuous mode
bridge0: port 2(bridge_slave_1) entered blocking state
bridge0: port 2(bridge_slave_1) entered disabled state
bridge_slave_1: entered allmulticast mode
bridge_slave_1: entered promiscuous mode
bond0: (slave bond_slave_0): Enslaving as an active interface with an up link
bond0: (slave bond_slave_1): Enslaving as an active interface with an up link
team0: Port device team_slave_0 added
team0: Port device team_slave_1 added
batman_adv: batadv0: Adding interface: batadv_slave_0
batman_adv: batadv0: The MTU of interface batadv_slave_0 is too small (1500) to handle the transport of batman-adv packets. Packets going over this interface will be fragmented on layer2 which could impact the performance. Setting the MTU to 1560 would solve the problem.
batman_adv: batadv0: Not using interface batadv_slave_0 (retrying later): interface not active
batman_adv: batadv0: Adding interface: batadv_slave_1
batman_adv: batadv0: The MTU of interface batadv_slave_1 is too small (1500) to handle the transport of batman-adv packets. Packets going over this interface will be fragmented on layer2 which could impact the performance. Setting the MTU to 1560 would solve the problem.
batman_adv: batadv0: Not using interface batadv_slave_1 (retrying later): interface not active
hsr_slave_0: entered promiscuous mode
hsr_slave_1: entered promiscuous mode
debugfs: 'hsr0' already exists in 'hsr'
Cannot create hsr debugfs directory
netdevsim netdevsim2 netdevsim0: renamed from eth0
netdevsim netdevsim2 netdevsim1: renamed from eth1
netdevsim netdevsim2 netdevsim2: renamed from eth2
netdevsim netdevsim2 netdevsim3: renamed from eth3
8021q: adding VLAN 0 to HW filter on device bond0
8021q: adding VLAN 0 to HW filter on device team0
8021q: adding VLAN 0 to HW filter on device batadv0
veth0_vlan: entered promiscuous mode
veth1_vlan: entered promiscuous mode
veth0_macvtap: entered promiscuous mode
veth1_macvtap: entered promiscuous mode


---
If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

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