syzbot

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BUG: KCSAN: data-race in fast_dput / lookup_fast

read-write to 0xffff88810609d0c0 of 4 bytes by task 5649 on cpu 0:
 retain_dentry fs/dcache.c:723 [inline]
 fast_dput+0x29f/0x2c0 fs/dcache.c:806
 dput+0x24/0xd0 fs/dcache.c:846
 step_into+0x182/0x810 fs/namei.c:1892
 handle_dots+0x3ec/0x750 fs/namei.c:2001
 walk_component fs/namei.c:2033 [inline]
 link_path_walk+0x62c/0x820 fs/namei.c:2404
 path_lookupat+0x72/0x2b0 fs/namei.c:2565
 filename_lookup+0x127/0x300 fs/namei.c:2595
 user_path_at+0x3c/0x110 fs/namei.c:3002
 do_mount fs/namespace.c:3809 [inline]
 __do_sys_mount fs/namespace.c:4020 [inline]
 __se_sys_mount+0x248/0x2d0 fs/namespace.c:3997
 __x64_sys_mount+0x67/0x80 fs/namespace.c:3997
 x64_sys_call+0x203e/0x2d60 arch/x86/include/generated/asm/syscalls_64.h:166
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88810609d0c0 of 4 bytes by task 5643 on cpu 1:
 d_revalidate fs/namei.c:867 [inline]
 lookup_fast+0xd9/0x2a0 fs/namei.c:1667
 walk_component fs/namei.c:2035 [inline]
 link_path_walk+0x464/0x820 fs/namei.c:2404
 path_lookupat+0x72/0x2b0 fs/namei.c:2565
 filename_lookup+0x127/0x300 fs/namei.c:2595
 user_path_at+0x3c/0x110 fs/namei.c:3002
 do_mount fs/namespace.c:3809 [inline]
 __do_sys_mount fs/namespace.c:4020 [inline]
 __se_sys_mount+0x248/0x2d0 fs/namespace.c:3997
 __x64_sys_mount+0x67/0x80 fs/namespace.c:3997
 x64_sys_call+0x203e/0x2d60 arch/x86/include/generated/asm/syscalls_64.h:166
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00280007 -> 0x00290047

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 5643 Comm: syz.2.416 Not tainted 6.11.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/27/2024
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