[moderation] [ext4?] KCSAN: data-race in __d_lookup_rcu / __d_rehash (6)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 98b1cc82c4af Linux 6.7-rc2
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15124324e80000
kernel config: https://syzkaller.appspot.com/x/.config?x=8c1151391aefc0c3
dashboard link: https://syzkaller.appspot.com/bug?extid=eda2491f39061694f590
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
CC: [adilger...@dilger.ca linux...@vger.kernel.org linux-...@vger.kernel.org linux-...@vger.kernel.org ty...@mit.edu]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/b63fb347c844/disk-98b1cc82.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/a75961292759/vmlinux-98b1cc82.xz
kernel image: https://storage.googleapis.com/syzbot-assets/52ef29cc01f9/bzImage-98b1cc82.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+eda249...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in __d_lookup_rcu / __d_rehash

read to 0xffff88811f17e6d0 of 8 bytes by task 3101 on cpu 1:
hlist_bl_unhashed include/linux/list_bl.h:54 [inline]
d_unhashed include/linux/dcache.h:336 [inline]
__d_lookup_rcu+0x120/0x290 fs/dcache.c:2399
lookup_fast+0x8e/0x290 fs/namei.c:1629
walk_component fs/namei.c:1998 [inline]
link_path_walk+0x3f4/0x7e0 fs/namei.c:2329
path_lookupat+0x72/0x2a0 fs/namei.c:2482
filename_lookup+0x126/0x300 fs/namei.c:2512
user_path_at_empty+0x42/0x110 fs/namei.c:2911
user_path_at include/linux/namei.h:57 [inline]
ksys_umount fs/namespace.c:1916 [inline]
__do_sys_umount fs/namespace.c:1924 [inline]
__se_sys_umount fs/namespace.c:1922 [inline]
__x64_sys_umount+0x88/0xe0 fs/namespace.c:1922
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x44/0x110 arch/x86/entry/common.c:82
entry_SYSCALL_64_after_hwframe+0x63/0x6b

write to 0xffff88811f17e6d0 of 8 bytes by task 3108 on cpu 0:
hlist_bl_add_head_rcu include/linux/rculist_bl.h:81 [inline]
__d_rehash+0xc4/0x220 fs/dcache.c:2578
__d_add+0x36d/0x4a0 fs/dcache.c:2793
d_splice_alias+0xd6/0x270 fs/dcache.c:3181
ext4_lookup+0x199/0x390 fs/ext4/namei.c:1883
lookup_one_qstr_excl+0xc0/0x180 fs/namei.c:1609
filename_create+0x14d/0x2b0 fs/namei.c:3876
do_mkdirat+0x63/0x2a0 fs/namei.c:4121
__do_sys_mkdirat fs/namei.c:4144 [inline]
__se_sys_mkdirat fs/namei.c:4142 [inline]
__x64_sys_mkdirat+0x50/0x60 fs/namei.c:4142
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x44/0x110 arch/x86/entry/common.c:82
entry_SYSCALL_64_after_hwframe+0x63/0x6b

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 3108 Comm: syz-executor.4 Not tainted 6.7.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/10/2023
==================================================================


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.