[moderation] [kernel?] KCSAN: data-race in do_sync_mmap_readahead / do_sync_mmap_readahead (10)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 9d9c1cfec01c Merge tag 'mm-nonmm-stable-2025-12-11-11-47' ..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14d65e1a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=b319ff1b6a2797ca
dashboard link: https://syzkaller.appspot.com/bug?extid=d120bbc65fa373916946
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
CC: [b...@alien8.de dave....@linux.intel.com h...@zytor.com linux-...@vger.kernel.org mi...@redhat.com tg...@linutronix.de x...@kernel.org]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/cb991ba74a41/disk-9d9c1cfe.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/0e67c3758c73/vmlinux-9d9c1cfe.xz
kernel image: https://storage.googleapis.com/syzbot-assets/9cb9dbbf6d15/bzImage-9d9c1cfe.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+d120bb...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in do_sync_mmap_readahead / do_sync_mmap_readahead

write to 0xffff8881040b5bd8 of 4 bytes by task 5969 on cpu 0:
do_sync_mmap_readahead+0x2cd/0x320 mm/filemap.c:-1
filemap_fault+0x336/0xb70 mm/filemap.c:3549
__do_fault+0xbc/0x200 mm/memory.c:5320
do_shared_fault mm/memory.c:5819 [inline]
do_fault mm/memory.c:5893 [inline]
do_pte_missing mm/memory.c:4401 [inline]
handle_pte_fault mm/memory.c:6273 [inline]
__handle_mm_fault mm/memory.c:6411 [inline]
handle_mm_fault+0xd9c/0x2c60 mm/memory.c:6580
do_user_addr_fault+0x3fe/0x1080 arch/x86/mm/fault.c:1387
handle_page_fault arch/x86/mm/fault.c:1476 [inline]
exc_page_fault+0x62/0xa0 arch/x86/mm/fault.c:1532
asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:618
rep_movs_alternative+0x33/0x90 arch/x86/lib/copy_user_64.S:60
copy_user_generic arch/x86/include/asm/uaccess_64.h:126 [inline]
raw_copy_to_user arch/x86/include/asm/uaccess_64.h:147 [inline]
_inline_copy_to_user include/linux/uaccess.h:206 [inline]
_copy_to_user+0x7c/0xa0 lib/usercopy.c:26
copy_to_user include/linux/uaccess.h:236 [inline]
msr_read+0xc9/0x160 arch/x86/kernel/msr.c:69
vfs_read+0x1a8/0x770 fs/read_write.c:570
ksys_read+0xda/0x1a0 fs/read_write.c:715
__do_sys_read fs/read_write.c:724 [inline]
__se_sys_read fs/read_write.c:722 [inline]
__x64_sys_read+0x40/0x50 fs/read_write.c:722
x64_sys_call+0x2889/0x3000 arch/x86/include/generated/asm/syscalls_64.h:1
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd8/0x2a0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

write to 0xffff8881040b5bd8 of 4 bytes by task 5978 on cpu 1:
do_sync_mmap_readahead+0x2cd/0x320 mm/filemap.c:-1
filemap_fault+0x336/0xb70 mm/filemap.c:3549
__do_fault+0xbc/0x200 mm/memory.c:5320
do_read_fault mm/memory.c:5755 [inline]
do_fault mm/memory.c:5889 [inline]
do_pte_missing mm/memory.c:4401 [inline]
handle_pte_fault mm/memory.c:6273 [inline]
__handle_mm_fault mm/memory.c:6411 [inline]
handle_mm_fault+0xfab/0x2c60 mm/memory.c:6580
faultin_page mm/gup.c:1126 [inline]
__get_user_pages+0x1024/0x1ed0 mm/gup.c:1428
populate_vma_page_range mm/gup.c:1860 [inline]
__mm_populate+0x243/0x3a0 mm/gup.c:1963
mm_populate include/linux/mm.h:3701 [inline]
vm_mmap_pgoff+0x232/0x2e0 mm/util.c:586
ksys_mmap_pgoff+0x268/0x310 mm/mmap.c:604
x64_sys_call+0x16bb/0x3000 arch/x86/include/generated/asm/syscalls_64.h:10
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd8/0x2a0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00000000 -> 0x00000020

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 5978 Comm: syz.6.807 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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