linux-kernel - [syzbot] [fs?] WARNING: suspicious RCU usage in proc_sys

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Message-ID: <686571dd.a70a0220.2b31f5.0001.GAE@google.com>
Date: Wed, 02 Jul 2025 10:52:29 -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: [syzbot] [fs?] WARNING: suspicious RCU usage in proc_sys_compare

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=17c4d3d4580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=70c16e4e191115d4
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=15403770580000

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+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
2 locks held by syz-executor/5897:
 #0: ffff888074b98190 (&sb->s_type->i_mutex_key#10){++++}-{4:4}, at: inode_lock_shared include/linux/fs.h:884 [inline]
 #0: ffff888074b98190 (&sb->s_type->i_mutex_key#10){++++}-{4:4}, at: lookup_slow+0x46/0x70 fs/namei.c:1824
 #1: ffff88803150c0d0 (&lockref->lock){+.+.}-{3:3}, at: spin_lock include/linux/spinlock.h:351 [inline]
 #1: ffff88803150c0d0 (&lockref->lock){+.+.}-{3:3}, at: d_wait_lookup fs/dcache.c:2537 [inline]
 #1: ffff88803150c0d0 (&lockref->lock){+.+.}-{3:3}, at: d_alloc_parallel+0xbe4/0x15e0 fs/dcache.c:2624

stack backtrace:
CPU: 0 UID: 0 PID: 5897 Comm: syz-executor 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_slow+0x116/0x3d0 fs/namei.c:1793
 lookup_slow+0x53/0x70 fs/namei.c:1825
 walk_component fs/namei.c:2129 [inline]
 link_path_walk+0x935/0xea0 fs/namei.c:2497
 path_openat+0x28c/0x3830 fs/namei.c:4042
 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: 0033:0x7f0fb218d211
Code: 75 57 89 f0 25 00 00 41 00 3d 00 00 41 00 74 49 80 3d 3a 83 1f 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:00007ffcf4d54bd0 EFLAGS: 00000202 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 0000000000080001 RCX: 00007f0fb218d211
RDX: 0000000000080001 RSI: 00007f0fb21eeb68 RDI: 00000000ffffff9c
RBP: 00007f0fb21eeb68 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000007
R13: 00007ffcf4d54c70 R14: 0000000000000009 R15: 0000000000000000
 </TASK>


---
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