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BUG: KCSAN: data-race in retain_dentry / step_into

write to 0xffff88800963bc00 of 4 bytes by task 10151 on cpu 0:
 d_lru_add fs/dcache.c:400 [inline]
 retain_dentry+0x199/0x260 fs/dcache.c:658
 dput+0x11e/0x430 fs/dcache.c:881
 __fput+0x3b3/0x4f0 fs/file_table.c:293
 ____fput+0x11/0x20 fs/file_table.c:313
 task_work_run+0x8e/0x110 kernel/task_work.c:140
 tracehook_notify_resume include/linux/tracehook.h:189 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:174 [inline]
 exit_to_user_mode_prepare+0x17c/0x1b0 kernel/entry/common.c:208
 __syscall_exit_to_user_mode_work kernel/entry/common.c:290 [inline]
 syscall_exit_to_user_mode+0x20/0x40 kernel/entry/common.c:301
 do_syscall_64+0x45/0x80 arch/x86/entry/common.c:56
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88800963bc00 of 4 bytes by task 10156 on cpu 1:
 __follow_mount_rcu fs/namei.c:1398 [inline]
 handle_mounts fs/namei.c:1455 [inline]
 step_into+0xec/0xec0 fs/namei.c:1769
 open_last_lookups fs/namei.c:3312 [inline]
 path_openat+0x105e/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: 1 PID: 10156 Comm: syz-executor.3 Not tainted 5.12.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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