Message-ID: <67b45276.050a0220.173698.004f.GAE@google.com>
Date: Tue, 18 Feb 2025 01:27:18 -0800
From: syzbot <syzbot+ecccecbc636b455f9084@...kaller.appspotmail.com>
To: bigeasy@...utronix.de, gregkh@...uxfoundation.org, 
	linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com, tj@...nel.org
Subject: [syzbot] [kernfs?] WARNING: suspicious RCU usage in kernfs_node_dentry

Hello,

syzbot found the following issue on:

HEAD commit:    253c82b3a2ce Add linux-next specific files for 20250217
git tree:       linux-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=15141898580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f984ff1d92cb4017
dashboard link: https://syzkaller.appspot.com/bug?extid=ecccecbc636b455f9084
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=175b7da4580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17141898580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/af8b0f79abb4/disk-253c82b3.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/463f7d416e09/vmlinux-253c82b3.xz
kernel image: https://storage.googleapis.com/syzbot-assets/07101e97dd04/bzImage-253c82b3.xz

The issue was bisected to:

commit 5b2fabf7fe8f745ff214ff003e6067b64f172271
Author: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Date:   Thu Feb 13 14:50:20 2025 +0000

    kernfs: Acquire kernfs_rwsem in kernfs_node_dentry().

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=15a9fda4580000
final oops:     https://syzkaller.appspot.com/x/report.txt?x=17a9fda4580000
console output: https://syzkaller.appspot.com/x/log.txt?x=13a9fda4580000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+ecccecbc636b455f9084@...kaller.appspotmail.com
Fixes: 5b2fabf7fe8f ("kernfs: Acquire kernfs_rwsem in kernfs_node_dentry().")

=============================
WARNING: suspicious RCU usage
6.14.0-rc2-next-20250217-syzkaller #0 Not tainted
-----------------------------
fs/kernfs/mount.c:243 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-executor215/5837:
 #0: ffff88802ab0b870 (&fc->uapi_mutex){+.+.}-{4:4}, at: __do_sys_fsconfig fs/fsopen.c:465 [inline]
 #0: ffff88802ab0b870 (&fc->uapi_mutex){+.+.}-{4:4}, at: __se_sys_fsconfig+0x9b2/0xf60 fs/fsopen.c:344
 #1: ffff8880355560e0 (&type->s_umount_key#46){+.+.}-{4:4}, at: __super_lock fs/super.c:56 [inline]
 #1: ffff8880355560e0 (&type->s_umount_key#46){+.+.}-{4:4}, at: super_lock+0x196/0x400 fs/super.c:120
 #2: ffff88801bef7148 (&root->kernfs_rwsem){++++}-{4:4}, at: class_rwsem_read_constructor include/linux/rwsem.h:241 [inline]
 #2: ffff88801bef7148 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_node_dentry+0xc3/0x2d0 fs/kernfs/mount.c:223

stack backtrace:
CPU: 0 UID: 0 PID: 5837 Comm: syz-executor215 Not tainted 6.14.0-rc2-next-20250217-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 12/27/2024
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
 lockdep_rcu_suspicious+0x226/0x340 kernel/locking/lockdep.c:6847
 kernfs_node_dentry+0x24b/0x2d0 fs/kernfs/mount.c:243
 cgroup_do_get_tree+0x248/0x390 kernel/cgroup/cgroup.c:2233
 cgroup_get_tree+0xbb/0x230 kernel/cgroup/cgroup.c:2272
 vfs_get_tree+0x90/0x2b0 fs/super.c:1759
 vfs_cmd_create+0xa0/0x1f0 fs/fsopen.c:225
 __do_sys_fsconfig fs/fsopen.c:467 [inline]
 __se_sys_fsconfig+0xa33/0xf60 fs/fsopen.c:344
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f09e41a2de9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 61 18 00 00 90 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:00007ffe4f61eba8 EFLAGS: 00000246 ORIG_RAX: 00000000000001af
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007f09e41a2de9
RDX: 0000000000000000 RSI: 0000000000000006 RDI: 0000000000000003
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f09e41ec036
R13: 00007ffe4f61ebe0 R14: 00007ffe4f61ec20 R15: 0000000000000000
 </TASK>

============================================
WARNING: possible recursive locking detected
6.14.0-rc2-next-20250217-syzkaller #0 Not tainted
--------------------------------------------
syz-executor215/5837 is trying to acquire lock:
ffff88801bef7148 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_dop_revalidate+0xa2/0x5d0 fs/kernfs/dir.c:1178

but task is already holding lock:
ffff88801bef7148 (&root->kernfs_rwsem){++++}-{4:4}, at: class_rwsem_read_constructor include/linux/rwsem.h:241 [inline]
ffff88801bef7148 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_node_dentry+0xc3/0x2d0 fs/kernfs/mount.c:223

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

       CPU0
       ----
  lock(&root->kernfs_rwsem);
  lock(&root->kernfs_rwsem);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

3 locks held by syz-executor215/5837:
 #0: ffff88802ab0b870 (&fc->uapi_mutex){+.+.}-{4:4}, at: __do_sys_fsconfig fs/fsopen.c:465 [inline]
 #0: ffff88802ab0b870 (&fc->uapi_mutex){+.+.}-{4:4}, at: __se_sys_fsconfig+0x9b2/0xf60 fs/fsopen.c:344
 #1: ffff8880355560e0 (&type->s_umount_key#46){+.+.}-{4:4}, at: __super_lock fs/super.c:56 [inline]
 #1: ffff8880355560e0 (&type->s_umount_key#46){+.+.}-{4:4}, at: super_lock+0x196/0x400 fs/super.c:120
 #2: ffff88801bef7148 (&root->kernfs_rwsem){++++}-{4:4}, at: class_rwsem_read_constructor include/linux/rwsem.h:241 [inline]
 #2: ffff88801bef7148 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_node_dentry+0xc3/0x2d0 fs/kernfs/mount.c:223

stack backtrace:
CPU: 1 UID: 0 PID: 5837 Comm: syz-executor215 Not tainted 6.14.0-rc2-next-20250217-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 12/27/2024
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
 print_deadlock_bug+0x483/0x620 kernel/locking/lockdep.c:3039
 check_deadlock kernel/locking/lockdep.c:3091 [inline]
 validate_chain+0x15e2/0x5920 kernel/locking/lockdep.c:3893
 __lock_acquire+0x1397/0x2100 kernel/locking/lockdep.c:5228
 lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5851
 down_read+0xb1/0xa40 kernel/locking/rwsem.c:1524
 kernfs_dop_revalidate+0xa2/0x5d0 fs/kernfs/dir.c:1178
 d_revalidate fs/namei.c:923 [inline]
 lookup_dcache fs/namei.c:1651 [inline]
 lookup_one_unlocked+0x23b/0x2d0 fs/namei.c:2972
 lookup_one_positive_unlocked fs/namei.c:3003 [inline]
 lookup_positive_unlocked+0x2b/0xb0 fs/namei.c:3043
 kernfs_node_dentry+0x139/0x2d0 fs/kernfs/mount.c:244
 cgroup_do_get_tree+0x248/0x390 kernel/cgroup/cgroup.c:2233
 cgroup_get_tree+0xbb/0x230 kernel/cgroup/cgroup.c:2272
 vfs_get_tree+0x90/0x2b0 fs/super.c:1759
 vfs_cmd_create+0xa0/0x1f0 fs/fsopen.c:225
 __do_sys_fsconfig fs/fsopen.c:467 [inline]
 __se_sys_fsconfig+0xa33/0xf60 fs/fsopen.c:344
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f09e41a2de9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 61 18 00 00 90 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:00007ffe4f61eba8 EFLAGS: 00000246 ORIG_RAX: 00000000000001af
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007f09e41a2de9
RDX: 0000000000000000 RSI: 0000000000000006 RDI: 0000000000000003
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f09e41ec036
R13: 00007ffe4f61ebe0 R14: 00007ffe4f61ec20 R15: 0000000000000000
 </TASK>


---
This report is generated by a bot. It may contain errors.
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For information about bisection process see: https://goo.gl/tpsmEJ#bisection

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

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If you want to overwrite report's subsystems, reply with:
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