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BUG: KCSAN: data-race in filemap_fault / filemap_map_pages

write to 0xffff88812b2d15ac of 4 bytes by task 7709 on cpu 1:
 do_sync_mmap_readahead mm/filemap.c:2384 [inline]
 filemap_fault+0xdbc/0x1120 mm/filemap.c:2486
 ext4_filemap_fault+0x5b/0x74 fs/ext4/inode.c:6008
 __do_fault+0xa8/0x1e0 mm/memory.c:3276
 do_read_fault mm/memory.c:3673 [inline]
 do_fault mm/memory.c:3802 [inline]
 handle_pte_fault mm/memory.c:4033 [inline]
 __handle_mm_fault+0x2611/0x2cf0 mm/memory.c:4163
 handle_mm_fault+0x21c/0x540 mm/memory.c:4200
 do_user_addr_fault arch/x86/mm/fault.c:1442 [inline]
 do_page_fault+0x4a4/0xa52 arch/x86/mm/fault.c:1517
 page_fault+0x34/0x40 arch/x86/entry/entry_64.S:1203

read to 0xffff88812b2d15ac of 4 bytes by task 7720 on cpu 0:
 filemap_map_pages+0x8be/0x9e0 mm/filemap.c:2625
 do_fault_around mm/memory.c:3634 [inline]
 do_read_fault mm/memory.c:3668 [inline]
 do_fault mm/memory.c:3802 [inline]
 handle_pte_fault mm/memory.c:4033 [inline]
 __handle_mm_fault+0x2974/0x2cf0 mm/memory.c:4163
 handle_mm_fault+0x21c/0x540 mm/memory.c:4200
 do_user_addr_fault arch/x86/mm/fault.c:1442 [inline]
 do_page_fault+0x4a4/0xa52 arch/x86/mm/fault.c:1517
 page_fault+0x34/0x40 arch/x86/entry/entry_64.S:1203

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 7720 Comm: syz-fuzzer Not tainted 5.6.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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