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BUG: KCSAN: data-race in iterate_dir / shrink_dentry_list

write to 0xffff888131c46d80 of 4 bytes by task 5073 on cpu 1:
 shrink_dentry_list+0x127/0x340 fs/dcache.c:423
 shrink_dcache_sb+0x188/0x2d0 fs/dcache.c:1296
 reconfigure_super+0x40f/0x4f0 fs/super.c:889
 do_umount_root fs/namespace.c:1571 [inline]
 do_umount fs/namespace.c:1644 [inline]
 path_umount+0xa38/0xa70 fs/namespace.c:1753
 ksys_umount fs/namespace.c:1776 [inline]
 __do_sys_umount fs/namespace.c:1781 [inline]
 __se_sys_umount fs/namespace.c:1779 [inline]
 __x64_sys_umount+0xb5/0xe0 fs/namespace.c:1779
 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 0xffff888131c46d80 of 4 bytes by task 5198 on cpu 0:
 fsnotify_parent include/linux/fsnotify.h:69 [inline]
 fsnotify_file include/linux/fsnotify.h:99 [inline]
 fsnotify_access include/linux/fsnotify.h:256 [inline]
 iterate_dir+0x27e/0x3c0 fs/readdir.c:69
 __do_sys_getdents64 fs/readdir.c:369 [inline]
 __se_sys_getdents64+0x8e/0x1a0 fs/readdir.c:354
 __x64_sys_getdents64+0x3f/0x50 fs/readdir.c:354
 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: 0x00280400 -> 0x00200000

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 5198 Comm: syz-executor.0 Tainted: G        W         5.15.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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