syzbot

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BUG: KCSAN: data-race in d_shrink_add / lookup_fast

read to 0xffff88812451c600 of 4 bytes by task 7997 on cpu 1:
 d_is_miss include/linux/dcache.h:394 [inline]
 d_is_negative include/linux/dcache.h:440 [inline]
 lookup_fast+0xdf/0x700 fs/namei.c:1575
 walk_component+0x6d/0xe80 fs/namei.c:1796
 link_path_walk.part.0+0x5d3/0xa90 fs/namei.c:2131
 link_path_walk fs/namei.c:2259 [inline]
 path_lookupat.isra.0+0x77/0x5a0 fs/namei.c:2307
 filename_lookup+0x145/0x2b0 fs/namei.c:2338
 user_path_at_empty+0x4c/0x70 fs/namei.c:2598
 user_path_at include/linux/namei.h:49 [inline]
 do_faccessat+0x137/0x470 fs/open.c:398
 __do_sys_access fs/open.c:450 [inline]
 __se_sys_access fs/open.c:448 [inline]
 __x64_sys_access+0x3f/0x50 fs/open.c:448
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

write to 0xffff88812451c600 of 4 bytes by task 7994 on cpu 0:
 d_shrink_add+0xfa/0x140 fs/dcache.c:429
 __dput_to_list fs/dcache.c:874 [inline]
 __dput_to_list+0xda/0xf0 fs/dcache.c:864
 shrink_dentry_list+0x101/0x1c0 fs/dcache.c:1119
 shrink_dcache_sb+0x107/0x1d0 fs/dcache.c:1240
 reconfigure_super+0x31a/0x570 fs/super.c:938
 do_remount fs/namespace.c:2551 [inline]
 do_mount+0x11b0/0x15a0 fs/namespace.c:3134
 ksys_mount+0xe8/0x160 fs/namespace.c:3352
 __do_sys_mount fs/namespace.c:3366 [inline]
 __se_sys_mount fs/namespace.c:3363 [inline]
 __x64_sys_mount+0x70/0x90 fs/namespace.c:3363
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 7994 Comm: syz-executor.0 Not tainted 5.4.0-rc3+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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