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BUG: KCSAN: data-race in shmem_fallocate / shmem_fault

write to 0xffff88811ba96e70 of 8 bytes by task 31842 on cpu 1:
 shmem_fallocate+0x262/0x890 mm/shmem.c:3709
 vfs_fallocate+0x3b6/0x400 fs/open.c:339
 madvise_remove mm/madvise.c:1046 [inline]
 madvise_vma_behavior+0x2a1/0x1ed0 mm/madvise.c:1360
 madvise_walk_vmas mm/madvise.c:1721 [inline]
 madvise_do_behavior+0x5ee/0xa20 mm/madvise.c:1937
 do_madvise+0x10e/0x190 mm/madvise.c:2030
 __do_sys_madvise mm/madvise.c:2039 [inline]
 __se_sys_madvise mm/madvise.c:2037 [inline]
 __x64_sys_madvise+0x64/0x80 mm/madvise.c:2037
 x64_sys_call+0x1c6b/0x3000 arch/x86/include/generated/asm/syscalls_64.h:29
 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

read to 0xffff88811ba96e70 of 8 bytes by task 31835 on cpu 0:
 shmem_fault+0x90/0x250 mm/shmem.c:2750
 __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+0xc2/0x310 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: 0x0000000000000000 -> 0xffffc900039efb48

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 31835 Comm: syz.8.22497 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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