[moderation] [ext4?] KCSAN: data-race in do_sendfile / generic_file_llseek_size (3)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 994d5c58e50e Merge tag 'hardening-v6.7-rc4' of git://git.k..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=157a521ce80000
kernel config: https://syzkaller.appspot.com/x/.config?x=efc18f367a3f97fa
dashboard link: https://syzkaller.appspot.com/bug?extid=016396bc5e843e4e563b
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/77b2fa385c10/disk-994d5c58.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/a10e02299372/vmlinux-994d5c58.xz
kernel image: https://storage.googleapis.com/syzbot-assets/73ebc6f961cc/bzImage-994d5c58.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+016396...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in do_sendfile / generic_file_llseek_size

read to 0xffff888160bcfb40 of 8 bytes by task 15986 on cpu 1:
vfs_setpos fs/read_write.c:61 [inline]
generic_file_llseek_size+0x17a/0x2a0 fs/read_write.c:130
ext4_llseek+0x166/0x190 fs/ext4/file.c:908
vfs_llseek fs/read_write.c:289 [inline]
ksys_lseek fs/read_write.c:302 [inline]
__do_sys_lseek fs/read_write.c:313 [inline]
__se_sys_lseek fs/read_write.c:311 [inline]
__x64_sys_lseek+0xe9/0x150 fs/read_write.c:311
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 0xffff888160bcfb40 of 8 bytes by task 15987 on cpu 0:
do_sendfile+0x76b/0x980 fs/read_write.c:1269
__do_sys_sendfile64 fs/read_write.c:1322 [inline]
__se_sys_sendfile64 fs/read_write.c:1308 [inline]
__x64_sys_sendfile64+0x110/0x150 fs/read_write.c:1308
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: 0x0000000000000000 -> 0x0000000000020400

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 15987 Comm: syz-executor.5 Tainted: G W 6.7.0-rc3-syzkaller-00134-g994d5c58e50e #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/10/2023
==================================================================


---
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

[syzbot]

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