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BUG: KCSAN: data-race in lookup_fast / shrink_dentry_list

write to 0xffff888107553300 of 4 bytes by task 31841 on cpu 1:
 shrink_dentry_list+0x127/0x540 fs/dcache.c:421
 prune_dcache_sb+0x72/0xa0 fs/dcache.c:1255
 super_cache_scan+0x23e/0x2e0 fs/super.c:105
 do_shrink_slab+0x28b/0x550 mm/vmscan.c:512
 shrink_slab+0xea/0x1c0 mm/vmscan.c:673
 drop_slab_node mm/vmscan.c:707 [inline]
 drop_slab+0xe5/0x160 mm/vmscan.c:717
 drop_caches_sysctl_handler+0xd0/0x1a0 fs/drop_caches.c:65
 proc_sys_call_handler+0x3dd/0x530 fs/proc/proc_sysctl.c:591
 proc_sys_write+0x1e/0x30 fs/proc/proc_sysctl.c:617
 call_write_iter include/linux/fs.h:1977 [inline]
 new_sync_write fs/read_write.c:518 [inline]
 vfs_write+0x6f9/0x7e0 fs/read_write.c:605
 ksys_write+0xce/0x180 fs/read_write.c:658
 __do_sys_write fs/read_write.c:670 [inline]
 __se_sys_write fs/read_write.c:667 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:667
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888107553300 of 4 bytes by task 6567 on cpu 0:
 d_revalidate fs/namei.c:822 [inline]
 lookup_fast+0x7b/0x350 fs/namei.c:1587
 open_last_lookups fs/namei.c:3258 [inline]
 path_openat+0x47e/0x21b0 fs/namei.c:3495
 do_filp_open+0xbd/0x1d0 fs/namei.c:3525
 do_sys_openat2+0xa3/0x250 fs/open.c:1187
 do_sys_open fs/open.c:1203 [inline]
 __do_sys_open fs/open.c:1211 [inline]
 __se_sys_open fs/open.c:1207 [inline]
 __x64_sys_open+0xe2/0x110 fs/open.c:1207
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 6567 Comm: systemd-udevd Not tainted 5.12.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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