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BUG: KCSAN: data-race in filemap_fault / filemap_fault

write to 0xffff88811f4c71ac of 4 bytes by task 4017 on cpu 1:
 do_sync_mmap_readahead mm/filemap.c:2408 [inline]
 filemap_fault+0x42f/0x11e0 mm/filemap.c:2510
 ext4_filemap_fault+0x4b/0x60 fs/ext4/inode.c:6060
 __do_fault mm/memory.c:3464 [inline]
 do_read_fault+0x41f/0x730 mm/memory.c:3857
 do_fault mm/memory.c:3985 [inline]
 handle_pte_fault mm/memory.c:4225 [inline]
 __handle_mm_fault mm/memory.c:4357 [inline]
 handle_mm_fault+0x135d/0x1930 mm/memory.c:4394
 do_user_addr_fault+0x393/0x810 arch/x86/mm/fault.c:1295
 handle_page_fault arch/x86/mm/fault.c:1365 [inline]
 exc_page_fault+0xb8/0x330 arch/x86/mm/fault.c:1418
 asm_exc_page_fault+0x1e/0x30 arch/x86/include/asm/idtentry.h:542

read to 0xffff88811f4c71ac of 4 bytes by task 8631 on cpu 0:
 do_sync_mmap_readahead mm/filemap.c:2407 [inline]
 filemap_fault+0x404/0x11e0 mm/filemap.c:2510
 ext4_filemap_fault+0x4b/0x60 fs/ext4/inode.c:6060
 __do_fault mm/memory.c:3464 [inline]
 do_read_fault+0x41f/0x730 mm/memory.c:3857
 do_fault mm/memory.c:3985 [inline]
 handle_pte_fault mm/memory.c:4225 [inline]
 __handle_mm_fault mm/memory.c:4357 [inline]
 handle_mm_fault+0x135d/0x1930 mm/memory.c:4394
 do_user_addr_fault+0x393/0x810 arch/x86/mm/fault.c:1295
 handle_page_fault arch/x86/mm/fault.c:1365 [inline]
 exc_page_fault+0xb8/0x330 arch/x86/mm/fault.c:1418
 asm_exc_page_fault+0x1e/0x30 arch/x86/include/asm/idtentry.h:542

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 8631 Comm: syz-fuzzer Not tainted 5.8.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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