[moderation] [fs?] KCSAN: data-race in __dentry_kill / fast_dput

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 4fbbed787267 Merge tag 'timers-core-2024-01-21' of git://g..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1013bae7e80000
kernel config: https://syzkaller.appspot.com/x/.config?x=ba10a94c8ea40fe5
dashboard link: https://syzkaller.appspot.com/bug?extid=f4714f42412e27001a49
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
CC: [bra...@kernel.org ja...@suse.cz linux-...@vger.kernel.org linux-...@vger.kernel.org vi...@zeniv.linux.org.uk]

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/ae1396ce8757/disk-4fbbed78.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/779af4d1028c/vmlinux-4fbbed78.xz
kernel image: https://storage.googleapis.com/syzbot-assets/88804f956fb9/bzImage-4fbbed78.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f4714f...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in __dentry_kill / fast_dput

write to 0xffff888106b20e50 of 8 bytes by task 4388 on cpu 0:
__d_drop fs/dcache.c:509 [inline]
__dentry_kill+0x135/0x4a0 fs/dcache.c:601
dput+0x54/0xc0 fs/dcache.c:845
do_unlinkat+0x257/0x4c0 fs/namei.c:4401
__do_sys_unlink fs/namei.c:4446 [inline]
__se_sys_unlink fs/namei.c:4444 [inline]
__x64_sys_unlink+0x30/0x40 fs/namei.c:4444
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0x59/0x120 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x63/0x6b

read to 0xffff888106b20e50 of 8 bytes by task 2764 on cpu 1:
hlist_bl_unhashed include/linux/list_bl.h:54 [inline]
d_unhashed include/linux/dcache.h:341 [inline]
retain_dentry fs/dcache.c:686 [inline]
fast_dput+0x62/0x2b0 fs/dcache.c:782
dput+0x24/0xc0 fs/dcache.c:839
handle_mounts fs/namei.c:1554 [inline]
step_into+0x21a/0x800 fs/namei.c:1839
walk_component+0x164/0x230 fs/namei.c:2007
lookup_last fs/namei.c:2458 [inline]
path_lookupat+0x10a/0x2a0 fs/namei.c:2482
filename_lookup+0x126/0x300 fs/namei.c:2511
user_path_at_empty+0x42/0x110 fs/namei.c:2920
do_readlinkat+0x92/0x210 fs/stat.c:499
__do_sys_readlink fs/stat.c:532 [inline]
__se_sys_readlink fs/stat.c:529 [inline]
__x64_sys_readlink+0x47/0x50 fs/stat.c:529
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0x59/0x120 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x63/0x6b

value changed: 0xffff88823771e0e0 -> 0x0000000000000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 2764 Comm: udevd Not tainted 6.7.0-syzkaller-13004-g4fbbed787267 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023
==================================================================


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