[moderation] [fs?] KCSAN: data-race in do_sendfile / ksys_write (17)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 6de23f81a5e0 Linux 7.0-rc1
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1297544a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=415aaebe6aa758e3
dashboard link: https://syzkaller.appspot.com/bug?extid=1cf87899dfb5e587b1b0
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
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/af79cd116c3f/disk-6de23f81.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/37a43b22fa04/vmlinux-6de23f81.xz
kernel image: https://storage.googleapis.com/syzbot-assets/0ad017da29c9/bzImage-6de23f81.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+1cf878...@syzkaller.appspotmail.com

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

write to 0xffff88811b0e52b0 of 8 bytes by task 27124 on cpu 0:
ksys_write+0x11c/0x1a0 fs/read_write.c:742
__do_sys_write fs/read_write.c:751 [inline]
__se_sys_write fs/read_write.c:748 [inline]
__x64_sys_write+0x40/0x50 fs/read_write.c:748
x64_sys_call+0x27e1/0x3020 arch/x86/include/generated/asm/syscalls_64.h:2
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

write to 0xffff88811b0e52b0 of 8 bytes by task 27147 on cpu 1:
do_sendfile+0x40d/0x650 fs/read_write.c:1386
__do_sys_sendfile64 fs/read_write.c:1433 [inline]
__se_sys_sendfile64 fs/read_write.c:1419 [inline]
__x64_sys_sendfile64+0x105/0x150 fs/read_write.c:1419
x64_sys_call+0x2dc4/0x3020 arch/x86/include/generated/asm/syscalls_64.h:41
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x0000000000000000 -> 0x0000000000000001

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 27147 Comm: syz.7.6128 Tainted: G W syzkaller #0 PREEMPT(full)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
==================================================================


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