syzbot

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BUG: KCSAN: data-race in __d_instantiate / fast_dput

write to 0xffff888133fe8540 of 4 bytes by task 16882 on cpu 0:
 __d_instantiate+0x2c5/0x3c0 fs/dcache.c:1985
 d_instantiate+0x50/0x90 fs/dcache.c:2010
 shmem_symlink+0x338/0x390 mm/shmem.c:3096
 vfs_symlink+0x23f/0x350 fs/namei.c:4250
 do_symlinkat+0x104/0x380 fs/namei.c:4279
 __do_sys_symlink fs/namei.c:4301 [inline]
 __se_sys_symlink fs/namei.c:4299 [inline]
 __x64_sys_symlink+0x52/0x60 fs/namei.c:4299
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x44/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888133fe8540 of 4 bytes by task 378 on cpu 1:
 fast_dput+0x14/0x1c0 fs/dcache.c:749
 dput+0x26/0x360 fs/dcache.c:875
 handle_mounts fs/namei.c:1502 [inline]
 step_into+0x468/0xee0 fs/namei.c:1800
 walk_component+0x1a1/0x360 fs/namei.c:1976
 lookup_last fs/namei.c:2425 [inline]
 path_lookupat+0x12d/0x3d0 fs/namei.c:2449
 filename_lookup+0x130/0x310 fs/namei.c:2478
 user_path_at_empty+0x3e/0x110 fs/namei.c:2801
 do_readlinkat+0x97/0x210 fs/stat.c:443
 __do_sys_readlink fs/stat.c:476 [inline]
 __se_sys_readlink fs/stat.c:473 [inline]
 __x64_sys_readlink+0x43/0x50 fs/stat.c:473
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x44/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x00000008 -> 0x00600008

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 378 Comm: systemd-udevd Not tainted 5.15.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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