==================================================================
BUG: KCSAN: data-race in filemap_fault / generic_write_end

write to 0xffff8880bb54b3f8 of 8 bytes by task 29996 on cpu 0:
 i_size_write include/linux/fs.h:876 [inline]
 generic_write_end+0x99/0x250 fs/buffer.c:2186
 ext4_da_write_end+0x57e/0x760 fs/ext4/inode.c:3091
 generic_perform_write+0x23b/0x390 mm/filemap.c:3512
 ext4_buffered_write_iter+0x2cc/0x3b0 fs/ext4/file.c:269
 ext4_file_write_iter+0x768/0x1060 include/linux/fs.h:784
 call_write_iter include/linux/fs.h:1882 [inline]
 new_sync_write fs/read_write.c:503 [inline]
 vfs_write+0x665/0x6f0 fs/read_write.c:578
 ksys_write+0xce/0x180 fs/read_write.c:631
 __do_sys_write fs/read_write.c:643 [inline]
 __se_sys_write fs/read_write.c:640 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:640
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff8880bb54b3f8 of 8 bytes by task 29998 on cpu 1:
 i_size_read include/linux/fs.h:854 [inline]
 filemap_fault+0x98c/0x1270 mm/filemap.c:2735
 ext4_filemap_fault+0x4b/0x60 fs/ext4/inode.c:6060
 __do_fault mm/memory.c:3450 [inline]
 do_cow_fault+0x1e7/0x7f0 mm/memory.c:3872
 do_fault mm/memory.c:3973 [inline]
 handle_pte_fault mm/memory.c:4211 [inline]
 __handle_mm_fault mm/memory.c:4346 [inline]
 handle_mm_fault+0x16ff/0x1af0 mm/memory.c:4444
 faultin_page mm/gup.c:878 [inline]
 __get_user_pages+0xa3d/0x1010 mm/gup.c:1090
 populate_vma_page_range mm/gup.c:1420 [inline]
 __mm_populate+0x24d/0x340 mm/gup.c:1468
 mm_populate include/linux/mm.h:2566 [inline]
 vm_mmap_pgoff+0x133/0x170 mm/util.c:511
 ksys_mmap_pgoff+0x2a8/0x380 mm/mmap.c:1596
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 29998 Comm: syz-executor.1 Not tainted 5.9.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
==================================================================