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BUG: KCSAN: data-race in lookup_fast / shrink_dentry_list

write to 0xffff888106af7c00 of 4 bytes by task 9745 on cpu 0:
 shrink_dentry_list+0x127/0x340 fs/dcache.c:423
 shrink_dcache_sb+0x188/0x2d0 fs/dcache.c:1296
 reconfigure_super+0x2aa/0x4f0 fs/super.c:889
 do_remount fs/namespace.c:2657 [inline]
 path_mount+0x148b/0x1d30 fs/namespace.c:3245
 do_mount fs/namespace.c:3266 [inline]
 __do_sys_mount fs/namespace.c:3474 [inline]
 __se_sys_mount+0x23d/0x2e0 fs/namespace.c:3451
 __x64_sys_mount+0x63/0x70 fs/namespace.c:3451
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0x90 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888106af7c00 of 4 bytes by task 1783 on cpu 1:
 d_revalidate fs/namei.c:842 [inline]
 lookup_fast+0x15f/0x350 fs/namei.c:1595
 walk_component+0x5c/0x350 fs/namei.c:1955
 link_path_walk+0x4ae/0x770 fs/namei.c:2282
 path_lookupat+0x8b/0x3d0 fs/namei.c:2437
 filename_lookup+0x118/0x3b0 fs/namei.c:2467
 user_path_at_empty+0x3b/0x50 fs/namei.c:2747
 user_path_at include/linux/namei.h:57 [inline]
 vfs_statx+0x98/0x290 fs/stat.c:203
 vfs_fstatat fs/stat.c:225 [inline]
 vfs_lstat include/linux/fs.h:3386 [inline]
 __do_sys_newlstat fs/stat.c:380 [inline]
 __se_sys_newlstat+0x46/0x250 fs/stat.c:374
 __x64_sys_newlstat+0x2d/0x40 fs/stat.c:374
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0x90 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x00280400 -> 0x00200000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 1783 Comm: syz-executor.2 Tainted: G        W         5.14.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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