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BUG: KCSAN: data-race in shmem_fallocate / shmem_fault

write to 0xffff88813d582980 of 8 bytes by task 3177 on cpu 0:
 shmem_fallocate+0x486/0x8e0 mm/shmem.c:2962
 vfs_fallocate+0x378/0x3e0 fs/open.c:324
 ksys_fallocate fs/open.c:347 [inline]
 __do_sys_fallocate fs/open.c:355 [inline]
 __se_sys_fallocate fs/open.c:353 [inline]
 __x64_sys_fallocate+0x79/0xc0 fs/open.c:353
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

read to 0xffff88813d582980 of 8 bytes by task 3178 on cpu 1:
 shmem_fault+0x9f/0x3f0 mm/shmem.c:2121
 __do_fault mm/memory.c:4198 [inline]
 do_read_fault mm/memory.c:4547 [inline]
 do_fault mm/memory.c:4670 [inline]
 do_pte_missing mm/memory.c:3664 [inline]
 handle_pte_fault mm/memory.c:4939 [inline]
 __handle_mm_fault mm/memory.c:5079 [inline]
 handle_mm_fault+0x1224/0x2c10 mm/memory.c:5233
 do_user_addr_fault arch/x86/mm/fault.c:1392 [inline]
 handle_page_fault arch/x86/mm/fault.c:1486 [inline]
 exc_page_fault+0x24d/0x650 arch/x86/mm/fault.c:1542
 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:570
 rep_movs_alternative+0x13/0xb0 arch/x86/lib/copy_user_64.S:40
 copy_user_generic arch/x86/include/asm/uaccess_64.h:112 [inline]
 raw_copy_from_user arch/x86/include/asm/uaccess_64.h:127 [inline]
 _copy_from_user+0x80/0xd0 lib/usercopy.c:23
 copy_from_user include/linux/uaccess.h:183 [inline]
 __do_sys_signalfd4 fs/signalfd.c:309 [inline]
 __se_sys_signalfd4 fs/signalfd.c:302 [inline]
 __x64_sys_signalfd4+0x8a/0xf0 fs/signalfd.c:302
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

value changed: 0x0000000000000000 -> 0xffffc9000e63be50

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 3178 Comm: syz-executor.3 Not tainted 6.5.0-rc4-syzkaller-00174-gc1a515d3c027 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2023
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