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BUG: KCSAN: data-race in retain_dentry / step_into

write to 0xffff888105e22600 of 4 bytes by task 11140 on cpu 1:
 retain_dentry+0x1de/0x260 fs/dcache.c:660
 dput+0x3d/0x360 fs/dcache.c:881
 __fput+0x3ab/0x4e0 fs/file_table.c:293
 ____fput+0x11/0x20 fs/file_table.c:313
 task_work_run+0xae/0x130 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+0x151/0x170 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+0x40/0x50 arch/x86/entry/common.c:56
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888105e22600 of 4 bytes by task 11159 on cpu 0:
 __d_entry_type include/linux/dcache.h:394 [inline]
 d_is_symlink include/linux/dcache.h:424 [inline]
 step_into+0x158/0xec0 fs/namei.c:1777
 walk_component+0x190/0x350 fs/namei.c:1949
 lookup_last fs/namei.c:2398 [inline]
 path_lookupat+0x12d/0x570 fs/namei.c:2422
 filename_lookup+0xff/0x390 fs/namei.c:2455
 user_path_at_empty+0x3b/0x50 fs/namei.c:2735
 user_path_at include/linux/namei.h:60 [inline]
 do_sys_truncate fs/open.c:133 [inline]
 __do_sys_truncate fs/open.c:147 [inline]
 __se_sys_truncate fs/open.c:145 [inline]
 __x64_sys_truncate+0x75/0x120 fs/open.c:145
 do_syscall_64+0x34/0x50 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 11159 Comm: syz-executor.2 Not tainted 5.12.0-rc8-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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