KCSAN: data-race in copy_mm / dup

Kernel	Title	Rank 🛈	Repro	Cause bisect	Fix bisect	Count	Last	Reported	Patched	Status
upstream	KCSAN: data-race in copy_mm / dup_mmap mm	6				1	232d	232d	0/29	auto-obsoleted due to no activity on 2025/08/10 08:41
upstream	KCSAN: data-race in copy_mm / dup_mmap (2) mm	6				1	143d	143d	0/29	auto-obsoleted due to no activity on 2025/11/07 16:48

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BUG: KCSAN: data-race in copy_mm / dup_mmap

read-write to 0xffff88810476edd0 of 4 bytes by task 14629 on cpu 0:
 do_raw_write_seqcount_begin include/linux/seqlock.h:431 [inline]
 mm_lock_seqcount_begin include/linux/mmap_lock.h:88 [inline]
 mmap_write_lock_killable include/linux/mmap_lock.h:355 [inline]
 dup_mmap+0xed/0xf00 mm/mmap.c:1726
 dup_mm kernel/fork.c:1529 [inline]
 copy_mm+0x119/0x370 kernel/fork.c:1581
 copy_process+0xcbd/0x1f10 kernel/fork.c:2221
 kernel_clone+0x16b/0x5b0 kernel/fork.c:2651
 __do_sys_clone kernel/fork.c:2792 [inline]
 __se_sys_clone kernel/fork.c:2776 [inline]
 __x64_sys_clone+0x143/0x180 kernel/fork.c:2776
 x64_sys_call+0x12d0/0x3000 arch/x86/include/generated/asm/syscalls_64.h:57
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xc0/0x2a0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88810476ec00 of 1664 bytes by task 14628 on cpu 1:
 dup_mm kernel/fork.c:1523 [inline]
 copy_mm+0xe1/0x370 kernel/fork.c:1581
 copy_process+0xcbd/0x1f10 kernel/fork.c:2221
 kernel_clone+0x16b/0x5b0 kernel/fork.c:2651
 __do_sys_clone kernel/fork.c:2792 [inline]
 __se_sys_clone kernel/fork.c:2776 [inline]
 __x64_sys_clone+0x143/0x180 kernel/fork.c:2776
 x64_sys_call+0x12d0/0x3000 arch/x86/include/generated/asm/syscalls_64.h:57
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xc0/0x2a0 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: 14628 Comm: syz.4.3331 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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