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BUG: KCSAN: data-race in do_sync_mmap_readahead / ondemand_readahead

write to 0xffff88810b62b598 of 8 bytes by task 8391 on cpu 0:
 do_sync_mmap_readahead+0x2e1/0x360 mm/filemap.c:2806
 filemap_fault+0x1d2/0xc30 mm/filemap.c:2898
 ext4_filemap_fault+0x4b/0x60 fs/ext4/inode.c:6196
 __do_fault mm/memory.c:3637 [inline]
 do_read_fault+0x2e1/0x530 mm/memory.c:3939
 do_fault mm/memory.c:4067 [inline]
 handle_pte_fault mm/memory.c:4318 [inline]
 __handle_mm_fault mm/memory.c:4453 [inline]
 handle_mm_fault+0x1019/0x1840 mm/memory.c:4551
 do_user_addr_fault+0x60c/0xc00 arch/x86/mm/fault.c:1390
 handle_page_fault arch/x86/mm/fault.c:1475 [inline]
 exc_page_fault+0x94/0x2a0 arch/x86/mm/fault.c:1531
 asm_exc_page_fault+0x1e/0x30 arch/x86/include/asm/idtentry.h:577

read to 0xffff88810b62b598 of 8 bytes by task 8370 on cpu 1:
 ondemand_readahead+0x15e/0x780 mm/readahead.c:462
 page_cache_async_ra+0x1aa/0x1d0 mm/readahead.c:607
 page_cache_async_readahead include/linux/pagemap.h:863 [inline]
 do_async_mmap_readahead+0x222/0x250 mm/filemap.c:2837
 filemap_fault+0x100/0xc30 mm/filemap.c:2892
 ext4_filemap_fault+0x4b/0x60 fs/ext4/inode.c:6196
 __do_fault mm/memory.c:3637 [inline]
 do_read_fault+0x2e1/0x530 mm/memory.c:3939
 do_fault mm/memory.c:4067 [inline]
 handle_pte_fault mm/memory.c:4318 [inline]
 __handle_mm_fault mm/memory.c:4453 [inline]
 handle_mm_fault+0x1019/0x1840 mm/memory.c:4551
 do_user_addr_fault+0x60c/0xc00 arch/x86/mm/fault.c:1390
 handle_page_fault arch/x86/mm/fault.c:1475 [inline]
 exc_page_fault+0x94/0x2a0 arch/x86/mm/fault.c:1531
 asm_exc_page_fault+0x1e/0x30 arch/x86/include/asm/idtentry.h:577

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 8370 Comm: syz-fuzzer Not tainted 5.12.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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