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BUG: KCSAN: data-race in generic_write_end / mpage_submit_page

read to 0xffff88812152b5a8 of 8 bytes by task 23 on cpu 0:
 mpage_submit_page+0x81/0x170 fs/ext4/inode.c:2248
 mpage_map_and_submit_buffers+0x331/0x520 fs/ext4/inode.c:2450
 mpage_map_and_submit_extent fs/ext4/inode.c:2584 [inline]
 ext4_writepages+0x147c/0x22e0 fs/ext4/inode.c:2897
 do_writepages+0x6b/0x170 mm/page-writeback.c:2342
 __writeback_single_inode+0xaf/0x8d0 fs/fs-writeback.c:1364
 writeback_sb_inodes+0x4ba/0xa50 fs/fs-writeback.c:1628
 __writeback_inodes_wb+0xe8/0x1b0 fs/fs-writeback.c:1697
 wb_writeback+0x557/0x6a0 fs/fs-writeback.c:1806
 wb_check_background_flush fs/fs-writeback.c:1874 [inline]
 wb_do_writeback fs/fs-writeback.c:1962 [inline]
 wb_workfn+0x697/0x950 fs/fs-writeback.c:1990
 process_one_work+0x3d4/0x890 kernel/workqueue.c:2269
 worker_thread+0xa0/0x800 kernel/workqueue.c:2415
 kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

write to 0xffff88812152b5a8 of 8 bytes by task 8409 on cpu 1:
 i_size_write include/linux/fs.h:875 [inline]
 generic_write_end+0xd0/0x1f0 fs/buffer.c:2143
 ext4_da_write_end+0x158/0x620 fs/ext4/inode.c:3217
 generic_perform_write+0x1d3/0x320 mm/filemap.c:3338
 __generic_file_write_iter+0x251/0x380 mm/filemap.c:3456
 ext4_file_write_iter+0x1fc/0xa40 fs/ext4/file.c:270
 call_write_iter include/linux/fs.h:1870 [inline]
 new_sync_write+0x388/0x4a0 fs/read_write.c:483
 __vfs_write+0xb1/0xc0 fs/read_write.c:496
 vfs_write fs/read_write.c:558 [inline]
 vfs_write+0x18a/0x390 fs/read_write.c:542
 ksys_write+0xd5/0x1b0 fs/read_write.c:611
 __do_sys_write fs/read_write.c:623 [inline]
 __se_sys_write fs/read_write.c:620 [inline]
 __x64_sys_write+0x4c/0x60 fs/read_write.c:620
 do_syscall_64+0xcf/0x2f0 arch/x86/entry/common.c:296
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 8409 Comm: syz-executor.1 Not tainted 5.3.0+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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