[moderation] [ext4?] KCSAN: data-race in __d_instantiate / step_into

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: bee0e7762ad2 Merge tag 'for-linus-iommufd' of git://git.ke..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10735866e80000
kernel config: https://syzkaller.appspot.com/x/.config?x=ac34c1f29a8029df
dashboard link: https://syzkaller.appspot.com/bug?extid=75a8d0ccf7b6bd015eb5
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
CC: [adilger...@dilger.ca bra...@kernel.org linux...@vger.kernel.org linux-...@vger.kernel.org linux-...@vger.kernel.org ty...@mit.edu 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/233be5f65dd2/disk-bee0e776.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/94423738a289/vmlinux-bee0e776.xz
kernel image: https://storage.googleapis.com/syzbot-assets/0b977463fa9a/bzImage-bee0e776.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+75a8d0...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in __d_instantiate / step_into

read-write to 0xffff888107afeb40 of 4 bytes by task 3701 on cpu 0:
__d_instantiate+0x2cd/0x3b0 fs/dcache.c:2010
d_instantiate+0x59/0x80 fs/dcache.c:2035
shmem_symlink+0x364/0x390 mm/shmem.c:3502
vfs_symlink+0xc2/0x1a0 fs/namei.c:4464
do_symlinkat+0xe3/0x340 fs/namei.c:4490
__do_sys_symlink fs/namei.c:4511 [inline]
__se_sys_symlink fs/namei.c:4509 [inline]
__x64_sys_symlink+0x56/0x60 fs/namei.c:4509
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

read to 0xffff888107afeb40 of 4 bytes by task 2779 on cpu 1:
__d_entry_type include/linux/dcache.h:386 [inline]
d_is_symlink include/linux/dcache.h:416 [inline]
step_into+0x12f/0x800 fs/namei.c:1845
walk_component+0x164/0x230 fs/namei.c:2008
lookup_last fs/namei.c:2459 [inline]
path_lookupat+0x10a/0x2a0 fs/namei.c:2483
filename_lookup+0x126/0x300 fs/namei.c:2512
user_path_at_empty+0x42/0x110 fs/namei.c:2911
do_readlinkat+0x92/0x210 fs/stat.c:494
__do_sys_readlink fs/stat.c:527 [inline]
__se_sys_readlink fs/stat.c:524 [inline]
__x64_sys_readlink+0x47/0x50 fs/stat.c:524
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

value changed: 0x00000008 -> 0x00600008

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 2779 Comm: udevd Not tainted 6.7.0-rc4-syzkaller-00009-gbee0e7762ad2 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/10/2023
==================================================================
loop2: p1 p2
loop2: p1 start 117442560 is beyond EOD, truncated
loop2: p2 start 10358798 is beyond EOD, truncated
loop2: p1 p2 p4
loop2: p1 start 117442560 is beyond EOD, truncated
loop2: p2 start 10358798 is beyond EOD, truncated
loop2: p4 size 15765248 extends beyond EOD, truncated


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