syzbot

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BUG: KCSAN: data-race in file_update_time / shmem_fallocate

write to 0xffff88811b37e6bc of 4 bytes by task 8476 on cpu 1:
 inode_set_mtime_to_ts include/linux/fs.h:1839 [inline]
 shmem_truncate_range mm/shmem.c:1233 [inline]
 shmem_fallocate+0x2df/0x840 mm/shmem.c:3687
 vfs_fallocate+0x3b6/0x400 fs/open.c:342
 madvise_remove mm/madvise.c:1049 [inline]
 madvise_vma_behavior+0x1920/0x1cf0 mm/madvise.c:1346
 madvise_walk_vmas mm/madvise.c:1669 [inline]
 madvise_do_behavior+0x5b7/0x970 mm/madvise.c:1885
 do_madvise+0x10e/0x190 mm/madvise.c:1978
 __do_sys_madvise mm/madvise.c:1987 [inline]
 __se_sys_madvise mm/madvise.c:1985 [inline]
 __x64_sys_madvise+0x64/0x80 mm/madvise.c:1985
 x64_sys_call+0x1f1a/0x3000 arch/x86/include/generated/asm/syscalls_64.h:29
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88811b37e6bc of 4 bytes by task 8444 on cpu 0:
 inode_get_mtime_nsec include/linux/fs.h:1825 [inline]
 inode_get_mtime include/linux/fs.h:1831 [inline]
 inode_needs_update_time fs/inode.c:2324 [inline]
 file_update_time+0x87/0x2b0 fs/inode.c:2371
 fault_dirty_shared_page+0xd9/0x3c0 mm/memory.c:3531
 do_shared_fault mm/memory.c:5808 [inline]
 do_fault mm/memory.c:5854 [inline]
 do_pte_missing mm/memory.c:4362 [inline]
 handle_pte_fault mm/memory.c:6195 [inline]
 __handle_mm_fault mm/memory.c:6336 [inline]
 handle_mm_fault+0x165d/0x2be0 mm/memory.c:6505
 do_user_addr_fault+0x630/0x1080 arch/x86/mm/fault.c:1336
 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

value changed: 0x01c6d633 -> 0x04c1c6b4

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 8444 Comm: syz.0.1809 Tainted: G        W           syzkaller #0 PREEMPT(voluntary) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
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