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BUG: KCSAN: data-race in do_sync_mmap_readahead / ondemand_readahead

write to 0xffff88812b9c10a4 of 4 bytes by task 22841 on cpu 0:
 do_sync_mmap_readahead+0x309/0x350 mm/filemap.c:2901
 filemap_fault+0x1c9/0x7b0 mm/filemap.c:2990
 ext4_filemap_fault+0x4b/0x60 fs/ext4/inode.c:6194
 __do_fault mm/memory.c:3721 [inline]
 do_read_fault mm/memory.c:4025 [inline]
 do_fault mm/memory.c:4153 [inline]
 handle_pte_fault mm/memory.c:4412 [inline]
 __handle_mm_fault mm/memory.c:4547 [inline]
 handle_mm_fault+0xe8d/0x1a70 mm/memory.c:4645
 do_user_addr_fault+0x609/0xc00 arch/x86/mm/fault.c:1390
 handle_page_fault arch/x86/mm/fault.c:1475 [inline]
 exc_page_fault+0x91/0x230 arch/x86/mm/fault.c:1531
 asm_exc_page_fault+0x1e/0x30 arch/x86/include/asm/idtentry.h:577

read to 0xffff88812b9c10a4 of 4 bytes by task 22809 on cpu 1:
 ondemand_readahead+0x4f8/0x7b0 mm/readahead.c:550
 page_cache_async_ra+0x165/0x190 mm/readahead.c:607
 page_cache_async_readahead include/linux/pagemap.h:902 [inline]
 do_async_mmap_readahead+0x217/0x260 mm/filemap.c:2930
 filemap_fault+0x106/0x7b0 mm/filemap.c:2984
 ext4_filemap_fault+0x4b/0x60 fs/ext4/inode.c:6194
 __do_fault mm/memory.c:3721 [inline]
 do_read_fault mm/memory.c:4025 [inline]
 do_fault mm/memory.c:4153 [inline]
 handle_pte_fault mm/memory.c:4412 [inline]
 __handle_mm_fault mm/memory.c:4547 [inline]
 handle_mm_fault+0xe8d/0x1a70 mm/memory.c:4645
 do_user_addr_fault+0x609/0xc00 arch/x86/mm/fault.c:1390
 handle_page_fault arch/x86/mm/fault.c:1475 [inline]
 exc_page_fault+0x91/0x230 arch/x86/mm/fault.c:1531
 asm_exc_page_fault+0x1e/0x30 arch/x86/include/asm/idtentry.h:577

value changed: 0x00000020 -> 0x00000008

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 22809 Comm: systemd-udevd Not tainted 5.13.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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