syzbot


WARNING: suspicious RCU usage in kernfs_node_dentry

Status: upstream: reported C repro on 2025/02/18 09:27
Subsystems: kernfs
[Documentation on labels]
Reported-by: syzbot+ecccecbc636b455f9084@syzkaller.appspotmail.com
Fix commit: kernfs: Drop kernfs_rwsem while invoking lookup_positive_unlocked().
Patched on: [], missing on: [ci-qemu-gce-upstream-auto ci-qemu-native-arm64-kvm ci-qemu-upstream ci-qemu-upstream-386 ci-qemu2-arm32 ci-qemu2-arm64 ci-qemu2-arm64-compat ci-qemu2-arm64-mte ci-qemu2-riscv64 ci-snapshot-upstream-root ci-upstream-bpf-kasan-gce ci-upstream-bpf-next-kasan-gce ci-upstream-gce-arm64 ci-upstream-gce-leak ci-upstream-kasan-badwrites-root ci-upstream-kasan-gce ci-upstream-kasan-gce-386 ci-upstream-kasan-gce-root ci-upstream-kasan-gce-selinux-root ci-upstream-kasan-gce-smack-root ci-upstream-kmsan-gce-386-root ci-upstream-kmsan-gce-root ci-upstream-linux-next-kasan-gce-root ci-upstream-net-kasan-gce ci-upstream-net-this-kasan-gce ci2-upstream-fs ci2-upstream-kcsan-gce ci2-upstream-usb]
First crash: 38d, last: 29d
Cause bisection: introduced by (bisect log) :
commit 5b2fabf7fe8f745ff214ff003e6067b64f172271
Author: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Thu Feb 13 14:50:20 2025 +0000

  kernfs: Acquire kernfs_rwsem in kernfs_node_dentry().

Crash: possible deadlock in kernfs_dop_revalidate (log)
Repro: C syz .config
  
Discussions (2)
Title Replies (including bot) Last reply
[PATCH] kernfs: Drop kernfs_rwsem while invoking lookup_positive_unlocked(). 5 (5) 2025/02/21 08:42
[syzbot] [kernfs?] WARNING: suspicious RCU usage in kernfs_node_dentry 0 (1) 2025/02/18 09:27

Sample crash report:
=============================
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>

Crashes (476):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/02/17 22:41 linux-next 253c82b3a2ce 9be4ace3 .config strace log report syz / log C [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: suspicious RCU usage in kernfs_node_dentry
2025/02/26 15:52 linux-next e5d3fd687aac d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: suspicious RCU usage in kernfs_node_dentry
2025/02/26 14:10 linux-next e5d3fd687aac d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: suspicious RCU usage in kernfs_node_dentry
2025/02/26 12:55 linux-next e5d3fd687aac d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: suspicious RCU usage in kernfs_node_dentry
2025/02/26 10:22 linux-next e5d3fd687aac d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: suspicious RCU usage in kernfs_node_dentry
2025/02/26 08:55 linux-next e5d3fd687aac d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: suspicious RCU usage in kernfs_node_dentry
2025/02/26 08:53 linux-next e5d3fd687aac d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: suspicious RCU usage in kernfs_node_dentry
2025/02/26 05:14 linux-next e5d3fd687aac d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: suspicious RCU usage in kernfs_node_dentry
2025/02/25 22:34 linux-next e5d3fd687aac d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: suspicious RCU usage in kernfs_node_dentry
2025/02/25 19:23 linux-next e5d3fd687aac d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: suspicious RCU usage in kernfs_node_dentry
2025/02/25 14:55 linux-next e5d3fd687aac d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: suspicious RCU usage in kernfs_node_dentry
2025/02/25 13:41 linux-next e5d3fd687aac d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: suspicious RCU usage in kernfs_node_dentry
2025/02/25 12:38 linux-next e5d3fd687aac d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: suspicious RCU usage in kernfs_node_dentry
2025/02/25 11:32 linux-next e5d3fd687aac d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: suspicious RCU usage in kernfs_node_dentry
2025/02/25 10:29 linux-next e5d3fd687aac d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: suspicious RCU usage in kernfs_node_dentry
2025/02/25 09:16 linux-next e5d3fd687aac d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: suspicious RCU usage in kernfs_node_dentry
2025/02/25 08:08 linux-next e5d3fd687aac d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: suspicious RCU usage in kernfs_node_dentry
2025/02/25 08:03 linux-next e5d3fd687aac d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: suspicious RCU usage in kernfs_node_dentry
2025/02/25 02:28 linux-next e5d3fd687aac d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: suspicious RCU usage in kernfs_node_dentry
2025/02/24 20:49 linux-next e5d3fd687aac d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: suspicious RCU usage in kernfs_node_dentry
2025/02/24 13:48 linux-next e5d3fd687aac d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: suspicious RCU usage in kernfs_node_dentry
2025/02/24 12:12 linux-next e5d3fd687aac d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: suspicious RCU usage in kernfs_node_dentry
2025/02/24 10:41 linux-next e5d3fd687aac d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: suspicious RCU usage in kernfs_node_dentry
2025/02/24 09:09 linux-next e5d3fd687aac d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: suspicious RCU usage in kernfs_node_dentry
2025/02/24 08:28 linux-next e5d3fd687aac d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: suspicious RCU usage in kernfs_node_dentry
2025/02/24 07:24 linux-next e5d3fd687aac d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: suspicious RCU usage in kernfs_node_dentry
2025/02/24 05:37 linux-next e5d3fd687aac d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: suspicious RCU usage in kernfs_node_dentry
2025/02/24 03:59 linux-next e5d3fd687aac d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: suspicious RCU usage in kernfs_node_dentry
2025/02/24 02:39 linux-next e5d3fd687aac d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: suspicious RCU usage in kernfs_node_dentry
2025/02/23 22:01 linux-next e5d3fd687aac d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: suspicious RCU usage in kernfs_node_dentry
2025/02/23 19:59 linux-next e5d3fd687aac d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: suspicious RCU usage in kernfs_node_dentry
2025/02/23 13:46 linux-next e5d3fd687aac d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: suspicious RCU usage in kernfs_node_dentry
2025/02/23 12:08 linux-next e5d3fd687aac d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: suspicious RCU usage in kernfs_node_dentry
2025/02/23 09:20 linux-next e5d3fd687aac d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: suspicious RCU usage in kernfs_node_dentry
2025/02/23 09:20 linux-next e5d3fd687aac d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: suspicious RCU usage in kernfs_node_dentry
2025/02/23 03:38 linux-next e5d3fd687aac d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: suspicious RCU usage in kernfs_node_dentry
2025/02/23 02:29 linux-next e5d3fd687aac d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: suspicious RCU usage in kernfs_node_dentry
2025/02/23 00:41 linux-next e5d3fd687aac d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: suspicious RCU usage in kernfs_node_dentry
2025/02/22 23:04 linux-next e5d3fd687aac d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: suspicious RCU usage in kernfs_node_dentry
2025/02/22 22:55 linux-next e5d3fd687aac d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: suspicious RCU usage in kernfs_node_dentry
2025/02/22 13:53 linux-next e5d3fd687aac d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: suspicious RCU usage in kernfs_node_dentry
2025/02/22 09:59 linux-next e5d3fd687aac d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: suspicious RCU usage in kernfs_node_dentry
2025/02/22 09:58 linux-next e5d3fd687aac d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: suspicious RCU usage in kernfs_node_dentry
2025/02/22 07:18 linux-next e5d3fd687aac d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: suspicious RCU usage in kernfs_node_dentry
2025/02/22 06:11 linux-next e5d3fd687aac d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: suspicious RCU usage in kernfs_node_dentry
* Struck through repros no longer work on HEAD.