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BUG: KCSAN: data-race in dentry_kill / fast_dput

write to 0xffff88811b1750d0 of 8 bytes by task 29455 on cpu 1:
 __d_drop fs/dcache.c:578 [inline]
 dentry_kill+0x139/0x500 fs/dcache.c:824
 finish_dput+0x16/0x1d0 fs/dcache.c:1001
 dput+0x48/0x50 fs/dcache.c:1042
 lookup_open fs/namei.c:4520 [inline]
 open_last_lookups fs/namei.c:4608 [inline]
 path_openat+0xd29/0x2000 fs/namei.c:4856
 do_file_open+0x16c/0x290 fs/namei.c:4888
 do_sys_openat2+0xa0/0x130 fs/open.c:1395
 do_sys_open fs/open.c:1401 [inline]
 __do_sys_openat fs/open.c:1417 [inline]
 __se_sys_openat fs/open.c:1412 [inline]
 __x64_sys_openat+0xf2/0x120 fs/open.c:1412
 x64_sys_call+0x1e39/0x3020 arch/x86/include/generated/asm/syscalls_64.h:258
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x136/0x3c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88811b1750d0 of 8 bytes by task 29456 on cpu 0:
 hlist_bl_unhashed include/linux/list_bl.h:54 [inline]
 d_unhashed include/linux/dcache.h:396 [inline]
 retain_dentry fs/dcache.c:872 [inline]
 fast_dput+0x64/0x2e0 fs/dcache.c:971
 dput+0x1f/0x50 fs/dcache.c:1040
 end_dirop fs/namei.c:2956 [inline]
 end_creating include/linux/namei.h:117 [inline]
 vfs_mkdir+0xb4/0x3e0 fs/namei.c:5284
 filename_mkdirat+0x138/0x300 fs/namei.c:5305
 __do_sys_mkdir fs/namei.c:5332 [inline]
 __se_sys_mkdir+0x31/0xf0 fs/namei.c:5329
 __x64_sys_mkdir+0x31/0x40 fs/namei.c:5329
 x64_sys_call+0x2eab/0x3020 arch/x86/include/generated/asm/syscalls_64.h:84
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x136/0x3c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0xffff8882376f51a0 -> 0x0000000000000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 29456 Comm: syz.7.7927 Tainted: G        W           syzkaller #0 PREEMPT(lazy) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
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