[moderation] [fs?] KCSAN: data-race in do_sendfile / do_writev

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: dd9b004b7ff3 Merge tag 'trace-v6.19-rc1' of git://git.kern..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=166903c2580000
kernel config: https://syzkaller.appspot.com/x/.config?x=b319ff1b6a2797ca
dashboard link: https://syzkaller.appspot.com/bug?extid=bc7d8693bd6f76921104
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
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/9e79d07095a9/disk-dd9b004b.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/17768b8878a0/vmlinux-dd9b004b.xz
kernel image: https://storage.googleapis.com/syzbot-assets/2990b6178ed7/bzImage-dd9b004b.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+bc7d86...@syzkaller.appspotmail.com

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

write to 0xffff88811b633a30 of 8 bytes by task 18098 on cpu 0:
do_writev+0x11a/0x210 fs/read_write.c:1105
__do_sys_writev fs/read_write.c:1171 [inline]
__se_sys_writev fs/read_write.c:1168 [inline]
__x64_sys_writev+0x45/0x50 fs/read_write.c:1168
x64_sys_call+0x1ba5/0x3000 arch/x86/include/generated/asm/syscalls_64.h:21
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd8/0x2c0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88811b633a30 of 8 bytes by task 18099 on cpu 1:
do_sendfile+0x246/0x650 fs/read_write.c:1343
__do_sys_sendfile64 fs/read_write.c:1431 [inline]
__se_sys_sendfile64 fs/read_write.c:1417 [inline]
__x64_sys_sendfile64+0x105/0x150 fs/read_write.c:1417
x64_sys_call+0x2db1/0x3000 arch/x86/include/generated/asm/syscalls_64.h:41
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd8/0x2c0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x0000000000000078 -> 0x0000000000000084

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 18099 Comm: syz.1.4013 Tainted: G W syzkaller #0 PREEMPT(voluntary)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
==================================================================


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