==================================================================
BUG: KCSAN: data-race in ext4_write_end / mpage_process_page_bufs

write to 0xffff888105f51a88 of 8 bytes by task 19697 on cpu 1:
 i_size_write include/linux/fs.h:916 [inline]
 ext4_update_inode_size fs/ext4/ext4.h:3421 [inline]
 ext4_write_end+0x1c9/0x7f0 fs/ext4/inode.c:1311
 ext4_da_write_end+0x93/0x730 fs/ext4/inode.c:3085
 generic_perform_write+0x23a/0x3d0 mm/filemap.c:3781
 ext4_buffered_write_iter+0x305/0x400 fs/ext4/file.c:269
 ext4_file_write_iter+0x2e7/0x11a0
 call_write_iter include/linux/fs.h:2163 [inline]
 new_sync_write fs/read_write.c:507 [inline]
 vfs_write+0x77d/0x8c0 fs/read_write.c:594
 ksys_write+0xce/0x180 fs/read_write.c:647
 __do_sys_write fs/read_write.c:659 [inline]
 __se_sys_write fs/read_write.c:656 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:656
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0x90 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888105f51a88 of 8 bytes by task 8715 on cpu 0:
 i_size_read include/linux/fs.h:894 [inline]
 mpage_process_page_bufs+0x34/0x560 fs/ext4/inode.c:2198
 mpage_prepare_extent_to_map+0x4e6/0x640 fs/ext4/inode.c:2632
 ext4_writepages+0x9e8/0x1d30 fs/ext4/inode.c:2804
 do_writepages+0x25b/0x3a0 mm/page-writeback.c:2364
 __writeback_single_inode+0x80/0x440 fs/fs-writeback.c:1616
 writeback_sb_inodes+0x563/0xd30 fs/fs-writeback.c:1881
 __writeback_inodes_wb fs/fs-writeback.c:1950 [inline]
 wb_writeback+0x2ff/0x6b0 fs/fs-writeback.c:2055
 wb_check_start_all fs/fs-writeback.c:2177 [inline]
 wb_do_writeback+0x330/0x510 fs/fs-writeback.c:2203
 wb_workfn+0xc8/0x520 fs/fs-writeback.c:2237
 process_one_work+0x402/0x910 kernel/workqueue.c:2297
 worker_thread+0x636/0xae0 kernel/workqueue.c:2444
 kthread+0x262/0x280 kernel/kthread.c:319
 ret_from_fork+0x1f/0x30

value changed: 0x000000000010a000 -> 0x000000000010c000

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 8715 Comm: kworker/u4:10 Not tainted 5.14.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: writeback wb_workfn
 (flush-7:2)
==================================================================