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BUG: KCSAN: data-race in __d_lookup / __d_rehash

write to 0xffff88811b94c3d0 of 8 bytes by task 6941 on cpu 1:
 hlist_bl_add_head_rcu include/linux/rculist_bl.h:91 [inline]
 __d_rehash+0xa4/0x1d0 fs/dcache.c:2714
 __d_add+0x326/0x490 fs/dcache.c:2942
 d_splice_alias_ops+0xe3/0x370 fs/dcache.c:3291
 d_splice_alias+0x1f/0x30 fs/dcache.c:3320
 simple_lookup+0xb7/0xd0 fs/libfs.c:81
 lookup_one_qstr_excl+0xc7/0x240 fs/namei.c:1810
 __start_dirop fs/namei.c:2920 [inline]
 start_dirop+0x3e/0x70 fs/namei.c:2942
 simple_start_creating+0xa2/0xd0 fs/libfs.c:2308
 debugfs_start_creating+0xcd/0x160 fs/debugfs/inode.c:397
 debugfs_create_dir+0x20/0x230 fs/debugfs/inode.c:575
 nsim_udp_tunnels_info_create+0xab/0x370 drivers/net/netdevsim/udp_tunnels.c:142
 nsim_init_netdevsim drivers/net/netdevsim/netdev.c:1056 [inline]
 nsim_create+0x2be/0x940 drivers/net/netdevsim/netdev.c:1154
 __nsim_dev_port_add+0x514/0x700 drivers/net/netdevsim/dev.c:1434
 nsim_dev_port_add_all+0x33/0xc0 drivers/net/netdevsim/dev.c:1495
 nsim_dev_reload_create drivers/net/netdevsim/dev.c:1547 [inline]
 nsim_dev_reload_up+0x312/0x490 drivers/net/netdevsim/dev.c:983
 devlink_reload+0x344/0x5a0 net/devlink/dev.c:475
 devlink_pernet_pre_exit+0xf9/0x260 net/devlink/core.c:578
 ops_pre_exit_list net/core/net_namespace.c:161 [inline]
 ops_undo_list+0xb5/0x420 net/core/net_namespace.c:235
 cleanup_net+0x37c/0x5b0 net/core/net_namespace.c:706
 process_one_work kernel/workqueue.c:3396 [inline]
 process_scheduled_works+0x56a/0xa50 kernel/workqueue.c:3479
 worker_thread+0x569/0x750 kernel/workqueue.c:3560
 kthread+0x223/0x270 kernel/kthread.c:436
 ret_from_fork+0x146/0x330 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

read to 0xffff88811b94c3d0 of 8 bytes by task 3870 on cpu 0:
 hlist_bl_unhashed include/linux/list_bl.h:54 [inline]
 d_unhashed include/linux/dcache.h:396 [inline]
 __d_lookup+0xf8/0x340 fs/dcache.c:2625
 lookup_fast+0x5e/0x320 fs/namei.c:1878
 walk_component fs/namei.c:2278 [inline]
 link_path_walk+0x523/0xdd0 fs/namei.c:2656
 path_lookupat+0x53/0x4c0 fs/namei.c:2812
 filename_lookup+0x18f/0x390 fs/namei.c:2842
 vfs_statx+0x96/0x170 fs/stat.c:353
 vfs_fstatat+0x118/0x170 fs/stat.c:373
 __do_sys_newfstatat fs/stat.c:538 [inline]
 __se_sys_newfstatat+0x55/0x3e0 fs/stat.c:532
 __x64_sys_newfstatat+0x55/0x70 fs/stat.c:532
 x64_sys_call+0xee6/0x2550 arch/x86/include/generated/asm/syscalls_64.h:263
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x112/0x360 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0xffff888237780808 -> 0xffff88811b86b788

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 3870 Comm: udevd Not tainted syzkaller #0 PREEMPT(lazy) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
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