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BUG: KCSAN: data-race in shmem_fallocate / shmem_fault

write to 0xffff88812e4b02d8 of 8 bytes by task 21943 on cpu 0:
 shmem_fallocate+0x22e/0x860 mm/shmem.c:3668
 vfs_fallocate+0x368/0x3b0 fs/open.c:338
 madvise_remove mm/madvise.c:1034 [inline]
 madvise_vma_behavior mm/madvise.c:1269 [inline]
 madvise_walk_vmas mm/madvise.c:1511 [inline]
 do_madvise+0x14da/0x2ad0 mm/madvise.c:1698
 __do_sys_madvise mm/madvise.c:1714 [inline]
 __se_sys_madvise mm/madvise.c:1712 [inline]
 __x64_sys_madvise+0x61/0x70 mm/madvise.c:1712
 x64_sys_call+0x23ab/0x2dc0 arch/x86/include/generated/asm/syscalls_64.h:29
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88812e4b02d8 of 8 bytes by task 21927 on cpu 1:
 shmem_fault+0x97/0x250 mm/shmem.c:2716
 __do_fault+0xb6/0x200 mm/memory.c:4988
 do_shared_fault mm/memory.c:5467 [inline]
 do_fault mm/memory.c:5541 [inline]
 do_pte_missing mm/memory.c:4058 [inline]
 handle_pte_fault mm/memory.c:5900 [inline]
 __handle_mm_fault mm/memory.c:6043 [inline]
 handle_mm_fault+0xc7d/0x2ac0 mm/memory.c:6212
 faultin_page mm/gup.c:1196 [inline]
 __get_user_pages+0xf6a/0x2350 mm/gup.c:1491
 __get_user_pages_locked mm/gup.c:1757 [inline]
 faultin_page_range+0x352/0x5d0 mm/gup.c:1981
 madvise_populate mm/madvise.c:965 [inline]
 do_madvise+0x42b/0x2ad0 mm/madvise.c:1695
 __do_sys_madvise mm/madvise.c:1714 [inline]
 __se_sys_madvise mm/madvise.c:1712 [inline]
 __x64_sys_madvise+0x61/0x70 mm/madvise.c:1712
 x64_sys_call+0x23ab/0x2dc0 arch/x86/include/generated/asm/syscalls_64.h:29
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x0000000000000000 -> 0xffffc90002043ca8

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 21927 Comm: syz.0.12779 Not tainted 6.14.0-rc5-syzkaller-00016-g48a5eed9ad58 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
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