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BUG: KCSAN: data-race in ext4_writepages / generic_write_end

write to 0xffff8881208da2f8 of 8 bytes by task 3843 on cpu 0:
 i_size_write include/linux/fs.h:878 [inline]
 generic_write_end+0x98/0x230 fs/buffer.c:2183
 ext4_da_write_end+0x26c/0x620 fs/ext4/inode.c:3068
 generic_perform_write+0x26a/0x3f0 mm/filemap.c:3798
 ext4_buffered_write_iter+0x222/0x330 fs/ext4/file.c:270
 ext4_file_write_iter+0x2e3/0x1210
 call_write_iter include/linux/fs.h:2050 [inline]
 new_sync_write fs/read_write.c:504 [inline]
 vfs_write+0x71c/0x890 fs/read_write.c:591
 ksys_write+0xe8/0x1a0 fs/read_write.c:644
 __do_sys_write fs/read_write.c:656 [inline]
 __se_sys_write fs/read_write.c:653 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:653
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff8881208da2f8 of 8 bytes by task 2020 on cpu 1:
 i_size_read include/linux/fs.h:856 [inline]
 mpage_submit_page fs/ext4/inode.c:2084 [inline]
 mpage_map_and_submit_buffers fs/ext4/inode.c:2336 [inline]
 mpage_map_and_submit_extent fs/ext4/inode.c:2475 [inline]
 ext4_writepages+0xfd9/0x1d00 fs/ext4/inode.c:2804
 do_writepages+0x1db/0x350 mm/page-writeback.c:2352
 __writeback_single_inode+0x81/0x590 fs/fs-writeback.c:1581
 writeback_sb_inodes+0x69e/0xdd0 fs/fs-writeback.c:1854
 __writeback_inodes_wb+0xb0/0x2a0 fs/fs-writeback.c:1923
 wb_writeback+0x280/0x650 fs/fs-writeback.c:2028
 wb_check_start_all fs/fs-writeback.c:2150 [inline]
 wb_do_writeback+0x418/0x600 fs/fs-writeback.c:2176
 wb_workfn+0x88/0x260 fs/fs-writeback.c:2209
 process_one_work+0x3d3/0x720 kernel/workqueue.c:2289
 worker_thread+0x618/0xa70 kernel/workqueue.c:2436
 kthread+0x1a9/0x1e0 kernel/kthread.c:376
 ret_from_fork+0x1f/0x30

value changed: 0x0000000000fcb000 -> 0x0000000000fcc000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 2020 Comm: kworker/u4:11 Not tainted 5.18.0-rc6-syzkaller-00009-gfeb9c5e19e91 #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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