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BUG: KCSAN: data-race in iterate_dir / shrink_dentry_list

write to 0xffff888105c05300 of 4 bytes by task 21256 on cpu 0:
 shrink_dentry_list+0x127/0x580 fs/dcache.c:423
 shrink_dcache_sb+0x10d/0x1c0 fs/dcache.c:1296
 reconfigure_super+0x2aa/0x4f0 fs/super.c:889
 do_remount fs/namespace.c:2639 [inline]
 path_mount+0x1442/0x1ce0 fs/namespace.c:3227
 do_mount fs/namespace.c:3248 [inline]
 __do_sys_mount fs/namespace.c:3456 [inline]
 __se_sys_mount+0x23d/0x2e0 fs/namespace.c:3433
 __x64_sys_mount+0x63/0x70 fs/namespace.c:3433
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888105c05300 of 4 bytes by task 19390 on cpu 1:
 fsnotify_parent include/linux/fsnotify.h:60 [inline]
 fsnotify_file include/linux/fsnotify.h:90 [inline]
 fsnotify_access include/linux/fsnotify.h:247 [inline]
 iterate_dir+0x24f/0x370 fs/readdir.c:69
 __do_sys_getdents64 fs/readdir.c:369 [inline]
 __se_sys_getdents64+0x7f/0x190 fs/readdir.c:354
 __x64_sys_getdents64+0x3f/0x50 fs/readdir.c:354
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 19390 Comm: syz-executor.2 Not tainted 5.12.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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