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BUG: KCSAN: data-race in __d_instantiate / step_into

read-write to 0xffff888108425000 of 4 bytes by task 3428 on cpu 1:
 __d_instantiate+0x2cd/0x3c0 fs/dcache.c:1855
 d_instantiate+0x59/0x80 fs/dcache.c:1880
 shmem_mknod+0x153/0x180 mm/shmem.c:3287
 vfs_mknod+0x2d4/0x310 fs/namei.c:4015
 do_mknodat+0x27b/0x420
 __do_sys_mknod fs/namei.c:4098 [inline]
 __se_sys_mknod fs/namei.c:4096 [inline]
 __x64_sys_mknod+0x53/0x60 fs/namei.c:4096
 x64_sys_call+0x9e9/0x2d70 arch/x86/include/generated/asm/syscalls_64.h:134
 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 0xffff888108425000 of 4 bytes by task 3427 on cpu 0:
 __follow_mount_rcu fs/namei.c:1485 [inline]
 handle_mounts fs/namei.c:1536 [inline]
 step_into+0xe7/0x810 fs/namei.c:1842
 open_last_lookups fs/namei.c:3601 [inline]
 path_openat+0x14f6/0x1fa0 fs/namei.c:3810
 do_filp_open+0xf7/0x200 fs/namei.c:3840
 do_sys_openat2+0xab/0x120 fs/open.c:1413
 do_sys_open fs/open.c:1428 [inline]
 __do_sys_open fs/open.c:1436 [inline]
 __se_sys_open fs/open.c:1432 [inline]
 __x64_sys_open+0xe6/0x110 fs/open.c:1432
 x64_sys_call+0x12d6/0x2d70 arch/x86/include/generated/asm/syscalls_64.h:3
 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: 0x00000008 -> 0x00500008

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 3427 Comm: syz.4.71 Not tainted 6.10.0-rc7-syzkaller-00003-g4376e966ecb7 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/07/2024
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