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BUG: KCSAN: data-race in __lookup_mnt / __se_sys_pivot_root

write to 0xffff888118782d98 of 8 bytes by task 20163 on cpu 0:
 unhash_mnt fs/namespace.c:1030 [inline]
 __do_sys_pivot_root fs/namespace.c:4456 [inline]
 __se_sys_pivot_root+0x850/0x1090 fs/namespace.c:4388
 __x64_sys_pivot_root+0x31/0x40 fs/namespace.c:4388
 x64_sys_call+0x1abf/0x2dc0 arch/x86/include/generated/asm/syscalls_64.h:156
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff888118782d98 of 8 bytes by task 20164 on cpu 1:
 __lookup_mnt+0xa0/0xf0 fs/namespace.c:839
 __follow_mount_rcu fs/namei.c:1592 [inline]
 handle_mounts fs/namei.c:1622 [inline]
 step_into+0x426/0x820 fs/namei.c:1952
 walk_component fs/namei.c:2120 [inline]
 link_path_walk+0x50e/0x830 fs/namei.c:2479
 path_lookupat+0x72/0x2b0 fs/namei.c:2635
 filename_lookup+0x150/0x340 fs/namei.c:2665
 user_path_at+0x3c/0x120 fs/namei.c:3072
 __do_sys_pivot_root fs/namespace.c:4404 [inline]
 __se_sys_pivot_root+0x10e/0x1090 fs/namespace.c:4388
 __x64_sys_pivot_root+0x31/0x40 fs/namespace.c:4388
 x64_sys_call+0x1abf/0x2dc0 arch/x86/include/generated/asm/syscalls_64.h:156
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0xffff888106a31d80 -> 0xffff8881004dccc0

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 20164 Comm: syz.0.5594 Tainted: G        W          6.14.0-rc7-syzkaller-00074-ga7f2e10ecd8f #0
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
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