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BUG: KCSAN: data-race in generic_write_end / mpage_submit_page

write to 0xffff88811daf0a38 of 8 bytes by task 16313 on cpu 1:
 i_size_write include/linux/fs.h:896 [inline]
 generic_write_end+0xac/0x2a0 fs/buffer.c:2187
 ext4_da_write_end+0x55e/0x6d0 fs/ext4/inode.c:3092
 generic_perform_write+0x233/0x380 mm/filemap.c:3310
 ext4_buffered_write_iter+0x2b1/0x390 fs/ext4/file.c:270
 ext4_file_write_iter+0x4a3/0xfd0 fs/ext4/file.c:498
 call_write_iter include/linux/fs.h:1907 [inline]
 aio_write+0x27e/0x340 fs/aio.c:1583
 __io_submit_one fs/aio.c:1842 [inline]
 io_submit_one+0x4b6/0xe10 fs/aio.c:1885
 __do_sys_io_submit fs/aio.c:1944 [inline]
 __se_sys_io_submit+0xf5/0x250 fs/aio.c:1914
 __x64_sys_io_submit+0x3f/0x50 fs/aio.c:1914
 do_syscall_64+0x71/0x120 arch/x86/entry/common.c:359
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88811daf0a38 of 8 bytes by task 16278 on cpu 0:
 i_size_read include/linux/fs.h:874 [inline]
 mpage_submit_page+0x67/0x170 fs/ext4/inode.c:2076
 mpage_map_and_submit_buffers fs/ext4/inode.c:2330 [inline]
 mpage_map_and_submit_extent fs/ext4/inode.c:2469 [inline]
 ext4_writepages+0x106b/0x1cb0 fs/ext4/inode.c:2782
 do_writepages+0x7b/0x150 mm/page-writeback.c:2354
 __filemap_fdatawrite_range+0x19b/0x1d0 mm/filemap.c:421
 __filemap_fdatawrite mm/filemap.c:429 [inline]
 filemap_flush+0x1f/0x30 mm/filemap.c:456
 ext4_alloc_da_blocks+0x4c/0x130 fs/ext4/inode.c:3146
 ext4_release_file+0x36/0x180 fs/ext4/file.c:142
 __fput+0x1df/0x460 fs/file_table.c:281
 ____fput+0x11/0x20 fs/file_table.c:314
 task_work_run+0x8e/0x110 kernel/task_work.c:123
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_usermode_loop arch/x86/entry/common.c:216 [inline]
 __prepare_exit_to_usermode+0x1c8/0x230 arch/x86/entry/common.c:246
 __syscall_return_slowpath arch/x86/entry/common.c:329 [inline]
 do_syscall_64+0xb9/0x120 arch/x86/entry/common.c:368
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 16278 Comm: syz-executor.1 Not tainted 5.8.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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