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BUG: KCSAN: data-race in d_alloc_parallel / d_set_d_op

read-write to 0xffff88811be5d6c0 of 4 bytes by task 24197 on cpu 1:
 d_set_d_op+0xfb/0x1f0 fs/dcache.c:1792
 proc_pident_instantiate+0x164/0x180 fs/proc/base.c:2653
 proc_pident_lookup+0x112/0x180 fs/proc/base.c:2676
 proc_tgid_base_lookup+0x2b/0x30 fs/proc/base.c:3388
 __lookup_slow+0x17a/0x230 fs/namei.c:1693
 lookup_slow+0x3c/0x60 fs/namei.c:1710
 walk_component fs/namei.c:2001 [inline]
 link_path_walk+0x648/0x7e0 fs/namei.c:2328
 path_openat+0x1a0/0x1d40 fs/namei.c:3794
 do_filp_open+0xf6/0x200 fs/namei.c:3825
 do_sys_openat2+0xab/0x110 fs/open.c:1404
 do_sys_open fs/open.c:1419 [inline]
 __do_sys_openat fs/open.c:1435 [inline]
 __se_sys_openat fs/open.c:1430 [inline]
 __x64_sys_openat+0xf3/0x120 fs/open.c:1430
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcd/0x1d0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x63/0x6b

read to 0xffff88811be5d6c0 of 4 bytes by task 24196 on cpu 0:
 d_in_lookup include/linux/dcache.h:365 [inline]
 d_wait_lookup fs/dcache.c:2443 [inline]
 d_alloc_parallel+0x5f9/0xc60 fs/dcache.c:2531
 __lookup_slow+0x8d/0x230 fs/namei.c:1678
 lookup_slow+0x3c/0x60 fs/namei.c:1710
 walk_component fs/namei.c:2001 [inline]
 link_path_walk+0x648/0x7e0 fs/namei.c:2328
 path_openat+0x1a0/0x1d40 fs/namei.c:3794
 do_filp_open+0xf6/0x200 fs/namei.c:3825
 do_sys_openat2+0xab/0x110 fs/open.c:1404
 do_sys_open fs/open.c:1419 [inline]
 __do_sys_openat fs/open.c:1435 [inline]
 __se_sys_openat fs/open.c:1430 [inline]
 __x64_sys_openat+0xf3/0x120 fs/open.c:1430
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcd/0x1d0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x63/0x6b

value changed: 0x10000000 -> 0x1000000c

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 24196 Comm: syz-executor.2 Not tainted 6.8.0-rc4-syzkaller-00005-gc664e16bb1ba #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/25/2024
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