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BUG: KCSAN: data-race in __dentry_kill / fast_dput

write to 0xffff888106688e50 of 8 bytes by task 5137 on cpu 1:
 __d_drop fs/dcache.c:549 [inline]
 __dentry_kill+0x13e/0x4c0 fs/dcache.c:641
 dput+0x5c/0xd0 fs/dcache.c:885
 handle_mounts fs/namei.c:1640 [inline]
 step_into+0x226/0x860 fs/namei.c:1966
 walk_component fs/namei.c:2134 [inline]
 link_path_walk+0x500/0x840 fs/namei.c:2493
 path_lookupat+0x6c/0x2a0 fs/namei.c:2649
 filename_lookup+0x14b/0x340 fs/namei.c:2679
 user_path_at+0x3c/0x140 fs/namei.c:3085
 __do_sys_pivot_root fs/namespace.c:4746 [inline]
 __se_sys_pivot_root+0xcd/0x1340 fs/namespace.c:4735
 __x64_sys_pivot_root+0x31/0x40 fs/namespace.c:4735
 x64_sys_call+0x2cc5/0x2e10 arch/x86/include/generated/asm/syscalls_64.h:156
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xc9/0x1c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff888106688e50 of 8 bytes by task 5136 on cpu 0:
 hlist_bl_unhashed include/linux/list_bl.h:54 [inline]
 d_unhashed include/linux/dcache.h:365 [inline]
 retain_dentry fs/dcache.c:726 [inline]
 fast_dput+0x65/0x2c0 fs/dcache.c:822
 dput+0x24/0xd0 fs/dcache.c:879
 handle_mounts fs/namei.c:1640 [inline]
 step_into+0x226/0x860 fs/namei.c:1966
 walk_component fs/namei.c:2134 [inline]
 link_path_walk+0x500/0x840 fs/namei.c:2493
 path_lookupat+0x6c/0x2a0 fs/namei.c:2649
 filename_lookup+0x14b/0x340 fs/namei.c:2679
 user_path_at+0x3c/0x140 fs/namei.c:3085
 __do_sys_pivot_root fs/namespace.c:4746 [inline]
 __se_sys_pivot_root+0xcd/0x1340 fs/namespace.c:4735
 __x64_sys_pivot_root+0x31/0x40 fs/namespace.c:4735
 x64_sys_call+0x2cc5/0x2e10 arch/x86/include/generated/asm/syscalls_64.h:156
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xc9/0x1c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0xffff888237898060 -> 0x0000000000000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 5136 Comm: syz.4.11078 Tainted: G        W          6.14.0-syzkaller-03576-g1e1ba8d23dae #0 PREEMPT(voluntary) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
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