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BUG: KCSAN: data-race in filemap_fault / filemap_map_pages

write to 0xffff88812b3d35ac of 4 bytes by task 8700 on cpu 0:
 do_sync_mmap_readahead mm/filemap.c:2487 [inline]
 filemap_fault+0x42f/0x11e0 mm/filemap.c:2589
 ext4_filemap_fault+0x4b/0x60 fs/ext4/inode.c:6060
 __do_fault mm/memory.c:3465 [inline]
 do_read_fault+0x41f/0x730 mm/memory.c:3858
 do_fault mm/memory.c:3986 [inline]
 handle_pte_fault mm/memory.c:4226 [inline]
 __handle_mm_fault mm/memory.c:4358 [inline]
 handle_mm_fault+0x14e9/0x1af0 mm/memory.c:4456
 do_user_addr_fault+0x380/0x770 arch/x86/mm/fault.c:1294
 handle_page_fault arch/x86/mm/fault.c:1351 [inline]
 exc_page_fault+0xb8/0x330 arch/x86/mm/fault.c:1404
 asm_exc_page_fault+0x1e/0x30 arch/x86/include/asm/idtentry.h:538

read to 0xffff88812b3d35ac of 4 bytes by task 8690 on cpu 1:
 filemap_map_pages+0x68d/0x990 mm/filemap.c:2727
 do_fault_around mm/memory.c:3819 [inline]
 do_read_fault+0x22f/0x730 mm/memory.c:3853
 do_fault mm/memory.c:3986 [inline]
 handle_pte_fault mm/memory.c:4226 [inline]
 __handle_mm_fault mm/memory.c:4358 [inline]
 handle_mm_fault+0x14e9/0x1af0 mm/memory.c:4456
 do_user_addr_fault+0x380/0x770 arch/x86/mm/fault.c:1294
 handle_page_fault arch/x86/mm/fault.c:1351 [inline]
 exc_page_fault+0xb8/0x330 arch/x86/mm/fault.c:1404
 asm_exc_page_fault+0x1e/0x30 arch/x86/include/asm/idtentry.h:538

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 8690 Comm: syz-fuzzer Not tainted 5.8.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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