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BUG: KCSAN: data-race in ext4_write_end / ext4_writepages

write to 0xffff888105dae210 of 8 bytes by task 32620 on cpu 0:
 i_size_write include/linux/fs.h:872 [inline]
 ext4_update_inode_size fs/ext4/ext4.h:3292 [inline]
 ext4_write_end+0x1d7/0x820 fs/ext4/inode.c:1311
 ext4_da_write_end+0x93/0x730 fs/ext4/inode.c:3081
 generic_perform_write+0x23e/0x3a0 mm/filemap.c:3586
 ext4_buffered_write_iter+0x2f2/0x3f0 fs/ext4/file.c:269
 ext4_file_write_iter+0x2e7/0x11d0 fs/ext4/file.c:502
 call_write_iter include/linux/fs.h:1977 [inline]
 new_sync_write fs/read_write.c:518 [inline]
 vfs_write+0x69d/0x770 fs/read_write.c:605
 ksys_write+0xce/0x180 fs/read_write.c:658
 __do_sys_write fs/read_write.c:670 [inline]
 __se_sys_write fs/read_write.c:667 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:667
 do_syscall_64+0x34/0x50 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888105dae210 of 8 bytes by task 8 on cpu 1:
 i_size_read include/linux/fs.h:850 [inline]
 mpage_submit_page fs/ext4/inode.c:2096 [inline]
 mpage_map_and_submit_buffers fs/ext4/inode.c:2350 [inline]
 mpage_map_and_submit_extent fs/ext4/inode.c:2489 [inline]
 ext4_writepages+0x1008/0x1d10 fs/ext4/inode.c:2802
 do_writepages+0x7b/0x150 mm/page-writeback.c:2352
 __writeback_single_inode+0x80/0x450 fs/fs-writeback.c:1467
 writeback_sb_inodes+0x564/0xf10 fs/fs-writeback.c:1732
 wb_writeback+0x28e/0x700 fs/fs-writeback.c:1905
 wb_do_writeback+0x101/0x510 fs/fs-writeback.c:2050
 wb_workfn+0xc8/0x520 fs/fs-writeback.c:2091
 process_one_work+0x3e9/0x8f0 kernel/workqueue.c:2275
 worker_thread+0x636/0xae0 kernel/workqueue.c:2421
 kthread+0x1d0/0x1f0 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 8 Comm: kworker/u4:0 Not tainted 5.12.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: writeback wb_workfn (flush-8:0)
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