[moderation] [block?] KCSAN: data-race in blkdev_open / queue_limits_commit_update

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: e8ab83e34bdc Merge tag 'arm64-fixes' of git://git.kernel.o..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12215b68580000
kernel config: https://syzkaller.appspot.com/x/.config?x=6bd11c5d4ce102b4
dashboard link: https://syzkaller.appspot.com/bug?extid=81f06fc24f9a9b5621b6
compiler: Debian clang version 20.1.2 (++20250402124445+58df0ef89dd6-1~exp1~20250402004600.97), Debian LLD 20.1.2
CC: [ax...@kernel.dk linux...@vger.kernel.org linux-...@vger.kernel.org]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/88632eb0eb01/disk-e8ab83e3.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/d3729be4a6d0/vmlinux-e8ab83e3.xz
kernel image: https://storage.googleapis.com/syzbot-assets/30c181800164/bzImage-e8ab83e3.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+81f06f...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in blkdev_open / queue_limits_commit_update

read to 0xffff888101ff887c of 4 bytes by task 3456 on cpu 0:
bdev_can_atomic_write include/linux/blkdev.h:1763 [inline]
blkdev_open+0x161/0x290 block/fops.c:649
do_dentry_open+0x646/0xa20 fs/open.c:956
vfs_open+0x37/0x1e0 fs/open.c:1086
do_open fs/namei.c:3880 [inline]
path_openat+0x1c5e/0x2170 fs/namei.c:4039
do_filp_open+0x109/0x230 fs/namei.c:4066
do_sys_openat2+0xa6/0x110 fs/open.c:1429
do_sys_open fs/open.c:1444 [inline]
__do_sys_openat fs/open.c:1460 [inline]
__se_sys_openat fs/open.c:1455 [inline]
__x64_sys_openat+0xf2/0x120 fs/open.c:1455
x64_sys_call+0x1af/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:258
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd0/0x1a0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

write to 0xffff888101ff87f8 of 176 bytes by task 5034 on cpu 1:
queue_limits_commit_update+0x4c/0x110 block/blk-settings.c:461
loop_configure+0x746/0x9f0 drivers/block/loop.c:1029
lo_ioctl+0x5f8/0x1560 drivers/block/loop.c:-1
blkdev_ioctl+0x34f/0x440 block/ioctl.c:704
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:906 [inline]
__se_sys_ioctl+0xcb/0x140 fs/ioctl.c:892
__x64_sys_ioctl+0x43/0x50 fs/ioctl.c:892
x64_sys_call+0x19a8/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:17
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd0/0x1a0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 5034 Comm: syz.2.635 Not tainted 6.15.0-rc4-syzkaller-00296-ge8ab83e34bdc #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/19/2025
==================================================================
loop2: detected capacity change from 0 to 128
FAT-fs (loop2): utf8 is not a recommended IO charset for FAT filesystems, filesystem will be case sensitive!
FAT-fs (loop2): Invalid FSINFO signature: 0x41615252, 0x80417272 (sector = 1)
batman_adv: batadv0: Adding interface: dummy0
batman_adv: batadv0: The MTU of interface dummy0 is too small (1500) to handle the transport of batman-adv packets. Packets going over this interface will be fragmented on layer2 which could impact the performance. Setting the MTU to 1560 would solve the problem.
batman_adv: batadv0: Interface activated: dummy0


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup