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BUG: KCSAN: data-race in filemap_map_pages / simple_write_end

write to 0xffff888129ffc650 of 8 bytes by task 15979 on cpu 0:
 i_size_write include/linux/fs.h:896 [inline]
 simple_write_end+0x1fa/0x330 fs/libfs.c:587
 generic_perform_write+0x23b/0x390 mm/filemap.c:3310
 __generic_file_write_iter+0x154/0x330 mm/filemap.c:3428
 generic_file_write_iter+0x2f3/0x3e0 mm/filemap.c:3460
 call_write_iter include/linux/fs.h:1907 [inline]
 new_sync_write fs/read_write.c:484 [inline]
 __vfs_write+0x2d8/0x340 fs/read_write.c:497
 vfs_write+0x19b/0x350 fs/read_write.c:559
 ksys_write+0xce/0x180 fs/read_write.c:612
 __do_sys_write fs/read_write.c:624 [inline]
 __se_sys_write fs/read_write.c:621 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:621
 do_syscall_64+0x51/0xb0 arch/x86/entry/common.c:359
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888129ffc650 of 8 bytes by task 15983 on cpu 1:
 i_size_read include/linux/fs.h:874 [inline]
 filemap_map_pages+0x654/0x990 mm/filemap.c:2625
 do_fault_around mm/memory.c:3818 [inline]
 do_read_fault+0x22f/0x730 mm/memory.c:3852
 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
 faultin_page mm/gup.c:887 [inline]
 __get_user_pages+0xac6/0x1150 mm/gup.c:1113
 populate_vma_page_range mm/gup.c:1452 [inline]
 __mm_populate+0x256/0x340 mm/gup.c:1500
 mm_populate include/linux/mm.h:2605 [inline]
 vm_mmap_pgoff+0x13b/0x170 mm/util.c:511
 ksys_mmap_pgoff+0x342/0x3a0 mm/mmap.c:1595
 do_syscall_64+0x51/0xb0 arch/x86/entry/common.c:359
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 15983 Comm: syz-executor.3 Not tainted 5.8.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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